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Chapter EEffects of the Oil, Natural Gas, and Coal Production Infrastructure on the Availability of Aggregate Resources and Other Land Uses, Northern Front Range of ColoradoBy Neil S. Fishman, William H. Langer, Curtt L. Coppage, and David W. Siple
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Oil, natural gas, and coal have been produced across much of the area underlying the plains immediately adjacent to the northern part of the Front Range of Colorado. More than 7,000 oil and (or) natural gas wells and some 130 abandoned coal mines are in the study area, which includes parts of Adams, Boulder, Denver, Larimer, and Weld Counties in eastern Colorado. Extraction of these energy resources requires a production infrastructure that remains in place throughout production; some of the infrastructure remains in place long after production ceases. Thus, production of energy resources can limit use of the land for other purposes including production of aggregate resources, development of urban and commercial buildings, and farming.
The petroleum-production infrastructure, exclusive of setbacks and easements, occupies as much as 1,300 acres of the land surface in the study area, much of which is devoted to access roads. Although most of this land area currently is classified as planted or cultivated, petroleum is also produced at many places on land classified as urban or commercial. Extensive urban/commercial development in northwestern Adams, southwestern Weld, and northeastern Boulder Counties is underway where (1) many petroleum wells already exist, (2) future exploration of petroleum is considered likely, and (3) continued urban growth is anticipated. With regard to effects on aggregate production, it can be demonstrated that at two separate sites approximately 123,000 tons and 358,000 tons of aggregate, respectively, will not be mined due to petroleum production.
Past coal mining has left behind an extensive network of coal-mine workings, some of which present hazards to uses of the overlying land surface. Subsidence of the land surface, due to the collapse of abandoned underground mine workings, presents challenges for most uses of the land. However, subsidence is most likely to affect the land surface where the mine workings are relatively shallow. Of the total land area in the Boulder-Weld coal field that overlies abandoned mine workings, only about 28 percent overlies relatively shallow abandoned workings and most of this land is classified as planted/cultivated. The potential effects of subsidence on urban development, although not large, remain a hazard, in part due to coal-mine fires that lead to collapse of abandoned mine workings long after mining ends and become an important factor in long-term land-use planning.
Significant attempts have been made to mitigate conflicts among those competing for use of the land. Petroleum producers are increasing efforts to work closely with governmental planners, aggregate production companies, developers, and farmers to minimize conflicts and promote good relations. Continued efforts toward mitigation of potential issues will promote better decisionmaking for future uses of the land.
Extraction of energy resources (oil, natural gas, and coal) requires construction of a production infrastructure (for example, extraction equipment, storage facilities, roads, and rail lines) that remains in place throughout resource production and, in some cases, long after extraction ceases. In general, the presence of the energy-production infrastructure restricts use of the underlying and adjacent land for other purposes. These restrictions are rooted in an energy-production com- pany’s ownership or lease of the mineral estate, which includes all or part of the valuable substances, such as oil, natural gas, metals, and gemstones, found in the subsurface in addition to an implied easement to use as much of the surface estate as is reasonably necessary to obtain the energy resources under the property. As such, energy-production companies are legally entitled to gain access to those surface areas reasonably necessary to explore for and produce the underlying resources, whether or not they own the surface estate. Nevertheless, mitigation of the disturbed land and (or) reasonable compensation is afforded the owner of the surface estate following exploration and (or) production.
In the northern part of the Front Range of Colorado and the land area immediately to the east (fig. 1), herein referred to as the northern Front Range Urban Corridor, thousands of active petroleum (oil and (or) natural gas) wells and some 130 abandoned coal mines are located in an area that has also experienced extensive population growth over the last 30 years. Furthermore, in this same geographic area, population growth rates are expected to exceed those predicted for the remainder of the United States for perhaps the next 20 years or more (Denver Regional Council of Governments, 2003; Colorado Department of Local Affairs, 2003). The area of continued population growth in the northern Front Range Urban Corridor is also favorable for continued exploration and development of additional petroleum resources (Cook, this volume; Higley and Cox, this volume). Although coal mining in the area has ceased, coal remaining in the ground may contain significant quantities of potentially recoverable natural gas (Roberts and Fishman, 2001; Wray and Koenig, 2001).
The northern Front Range Urban Corridor also overlies important quantities of aggregate resources, including sand, gravel, and crushed stone (Knepper and others, 2001), all of which are used in large volumes in the construction and maintenance of urban and commercial structures. Aggregate is used in the construction of roads, sidewalks, building foundations, airports, and other facilities necessary for the sustainability, vitality, and growth of any populated area, and it also is used as a raw material in building products such as concrete, asphalt, shingles, and brick. Nevertheless, the availability of aggregate resources in the northern Front Range Urban Corridor can be limited through land-use regulations. Furthermore, development of other natural resources, including petroleum, can also limit the volume of aggregate available for use (Fishman and others, 1999). Thus, there is growing concern as to how land is used by groups with, at times, competing interests.
The results of a study to better understand the effects of energy resource production on land use are presented in this paper. The geographic extent of our study was confined to approximately 2,200 mi2 in the northern Front Range Urban Corridor in an area that also includes the rapidly urbanizing parts of Adams, Boulder, Denver, Larimer, and Weld Counties (fig. 1). Of particular interest is the manner by which the infrastructure required for the production of energy resources affects availability of aggregate resources (gravel and sand) in addition to other uses of the land surface. We also present examples of how companies, working cooperatively and constructively with others, have found ways to mitigate conflicts that arose from competing interests in use of the land in this region.
To more fully understand how production of petroleum and coal resources may affect other land uses, we provide a brief overview of these resources as well as an overview of aggregate resources in the region. Also included is a discussion of the nature of urban growth in recent years, particularly as it bears on conflicts with development of energy resources.
Although petroleum was first produced along the Front Range over 130 years ago (Higley and Cox, this volume), only in the past 30 years have large volumes of petroleum been discovered and produced. Much of the more recent exploration and production has been focused in the greater Wattenberg area (GWA), the geographic extent of which (fig. 1) was defined for regulatory purposes by the Colorado Oil and Gas Conservation Commission (an agency of the State of Colorado) to ensure the responsible development of petroleum resources. The study area for this project encompasses the western part of the GWA (fig. 1). Currently there are more than 7,000 wells that produce oil, gas, or both in the study area, and permitting continues for drilling of new wells. Production through 2000 from the entire GWA, which includes numerous individual oil and natural gas fields within and outside of the study area, has exceeded 2 trillion cubic feet of gas and more than 245 million barrels of oil (Higley and Cox, this volume). Accessibility to local markets in the Front Range has made the GWA an important energy-producing province in Colorado.
Rocks of Cretaceous age serve as both reservoir and source rocks for the petroleum produced in the study area, although some production also occurs from rocks of Permian age (fig. 2). The dominant Cretaceous producing formations include the (1) Muddy (“J”) Sandstone of the Dakota Group; (2) other sandstones in the Dakota Group including the Plainview (“Dakota” of drillers) and Lytle Formations (“Lakota” of drillers); (3) “D” sandstone of the Graneros Shale; (4) Codell Sandstone Member of the Carlile Shale; (5) Niobrara Formation; and (6) Terry “Sussex” Sandstone, Hygiene “Shannon” Sandstone, and Sharon Springs Members of the Pierre Shale (fig. 2). Oil is the principal resource produced from sandstones in the Pierre Shale, whereas oil or natural gas or both may be produced from the other formations of Cretaceous age (Higley and Cox, this volume). Oil is also produced from wells drilled into the Permian Lyons Sandstone (fig. 2). Source rocks for most of the petroleum produced in the GWA include the Cretaceous Mowry, Graneros, and Carlile Shales and the Greenhorn Limestone (fig. 2) (Weimer, 1996; Higley and Cox, this volume). The Skull Creek Shale may have also served as a source rock, although to a lesser degree than the others (Higley and Cox, this volume).
Because current estimates are that petroleum production in the GWA will continue for at least another 30 years (Higley and Cox, this volume), the production infrastructure will remain throughout this period of time. The nature of the production infrastructure required for any given petroleum well, and hence the land-surface area devoted to it, varies across the study area. A pump jack (fig. 3A) is used where significant pumping capacity is needed to bring petroleum and associated waters to the surface, as is the case for most wells that produce from the sandstones in the Pierre Shale and the Lyons Sandstone. Once at the surface, the produced fluids (petroleum and possibly water) undergo preliminary processing onsite, which typically requires a water/oil/gas separator (fig. 3B) and tanks to store oil and associated produced water (fig. 3C), although several wells that individually produce low volumes of oil and water may share a single separator and storage tank. Field observations reveal that in places, only one battery of tanks and associated separation equipment may be necessary for as many as five oil wells. In contrast, a well that produces natural gas and little or no other fluid (oil or water) generally requires a smaller site for the wellhead (fig. 3D) than that used for a pump jack because no pumping equipment is needed. Pipelines are required between wells and production facilities (oil tank, water pit, and separator) as well as to transport natural gas from the lease. Though buried, pipelines usually require some access for maintenance and repair, which is why an easement is present around them. A road is required to all producing wells (fig. 3E) and to appropriate pumping and storage equipment so operators may have ready access to wells and associated equipment for monitoring and maintenance. Commonly, flow lines that direct petroleum and produced water from a well to storage or transfer equipment are placed under access roads to minimize surface disruption of the production equipment.
Coal was first produced along the Front Range in the early 1860s in the southwestern part of the currently defined Boulder-Weld coal field (BWCF) in Boulder and Weld Counties (fig. 1). Coal from the BWCF was mined continuously until the last mine was closed in 1979 (Kirkham and Ladwig, 1980). In addition to the BWCF, coal was produced in other Front Range counties (Kirkham and Ladwig, 1980; Roberts, this volume). Focus in this report, however, will be on the coal mines in the BWCF because of the wealth of data that are available for the more than 130 mines in the coal field. Coal produced from the BWCF totaled approximately 107 million short tons, which represents more than 82 percent of all the coal mined throughout the northern Front Range (Kirkham and Ladwig, 1980; Tremain and others, 1996).
The Cretaceous Laramie Formation (fig. 2) is the dominant coal-producing interval in the region (Kirkham and Ladwig, 1979; Roberts and Kirschbaum, 1995; Weimer, 1996). The overlying Tertiary Denver Formation (fig. 2) has produced a minor amount of lignite. Laramie Formation coal has a rank ranging from subbituminous B to subbituminous C, with a sulfur content of generally less than 1 percent (Kirkham and Ladwig, 1979) and a heating value as much as 9,000 BTU (Roberts, this volume). Coal from the Laramie Formation was used locally, as well as in the numerous mining towns and camps in the nearby mountains (Tremain and others, 1996), for both domestic and industrial purposes.
The production infrastructure needed to mine coal can be extensive and includes the mine workings (fig. 4A) and associated buildings, rail lines, and coal preparation/loadout facilities (fig. 4B). Within the study area, most of the mining-related infrastructure has been removed and much of the affected land surface reclaimed for post-mining urban or commercial development (Roberts, this volume). Virtually all coal from the BWCF was mined underground, generally at depths ranging from less than 50 ft to approximately 500 ft (Myers and others, 1975; Roberts and others, 2001). Extraction of coal from mines in the BWCF was accomplished using “room-and-pillar” mining methods (Myers and others, 1975; Roberts and others, 2001), whereby coal is mined from “rooms” whereas “pillars” are left between mined-out rooms to support the mine roof (fig. 5).
The method of coal mining in the BWCF and depth to coal are of importance because both influence the stability of the land surface overlying the mines. Locally, rooms in some of the abandoned mine workings have collapsed (Myers and others, 1975; Hynes, 1987; Herring and others, 1986; Roberts, this volume), and progressive upward caving of the overlying rock and soil has resulted. Locally, this caving has caused physical disruption, or subsidence, of the land surface (fig. 6).
The degree to which the land surface over abandoned coal mines in the BWCF has subsided varies, ranging from well-developed collapse pits to no obvious surface expression of subsidence (Myers and others, 1975; Hynes, 1987; Turney, 1985; Herring and others, 1986; Roberts, this volume). Although it is exceedingly difficult to accurately identify the subsidence potential in the BWCF, investigations have documented strongly developed subsidence features overlying some shallow (less than100 ft deep) mines, whereas well-defined subsidence features are difficult to identify where undermining was deeper (more than 200 ft) (Myers and others, 1975).
Coal-mine fires in the BWCF remain a concern; fires have been documented in the coal field as recently as 1988 (Rushworth and others, 1989). In addition to the threat of a fire as it bears on public safety, coal-mine fires can actually promote subsidence as pillars and other supporting features in the abandoned mines burn, which thereby compromises remaining support in the abandoned mine. The long-term effects of underground coal mines on land use are largely a function of the subsidence potential of mined-out areas.
Urban and commercial growth in the Front Range Urban Corridor has increased the demand for aggregate resources (Wilburn and Langer, 2000). For economic reasons, most aggregate used in the region has come from sources within approximately 40 miles of the market area (Socolow, 1995). Most historical sand and gravel mining within the study area took place in the valleys of major drainages including the Big Thompson River, Boulder Creek, Cache La Poudre River, Clear Creek, Saint Vrain Creek, and South Platte River (fig. 7). Depletion of some of these local sources of sand and gravel, as well as zoning restrictions, land-use conflicts, urban development, and environmental concerns, has resulted in a progressive downstream migration of sand and gravel extraction operations, particularly along the South Platte River (Arbogast and others, 2002; Lindsey and others, 1998).
Approximately 80 percent of the aggregate used in the Front Range is extracted from accumulations of surficial (Quaternary) deposits of sand and gravel (fig. 2; Knepper and others, 2001). In the Front Range, sand and gravel was deposited by streams in flood-plain and alluvial-fan depositional settings (Lindsey and Langer, 1999). Principal sources of high-quality aggregate are found in the Piney Creek, Broadway, and Louviers Alluvium, which are outwash units of Quaternary age in the study area.
Generally, for deposits along the Front Range, a large volume of coarse gravel rather than silt and (or) clay provides a good measure of the economic value of the deposit. A greater volume of coarse particles is desired because much of this coarser material is eventually used in concrete, asphalt, or road base or for other construction applications (Knepper and others, 2001). A persistent decrease in the coarseness and, therefore, the amount of valuable gravel compared to less valuable sand in aggregate deposits away (downstream) from the mountain front (Langer and Lindsey, 1999) results from the downstream decrease in carrying capacity of streams and rivers (Wilburn and Langer, 2000). The gravel content of the South Platte River locally increases where tributaries issuing from the nearby mountain front provide an influx of coarse aggregate (Wilburn and Langer, 2000). Even though aggregate deposits farther from the mountain front contain fewer coarse (more than 0.25 inch in diameter) particles, fine (less than 0.25 inch in diameter) particles from those deposits may be mined and combined either with coarse aggregate from elsewhere or crushed stone from local Front Range rock quarries to make a marketable product. Because these deposits contain less gravel than those closer to the mountains, more aggregate must be removed to meet the growing needs of consumers (Langer and Lindsey, 1999; Knepper and others, 2001).
Highest quality aggregate deposits, those that contain an abundance of competent, coarse particles, typically are in flood-plain and low terraces associated with major streams or rivers in the area, whereas aggregate deposits underlying intermediate terraces are commonly of medium quality because they contain more-weathered (degraded) coarse particles and more silt and clay than high-quality aggregate (Langer and Lindsey, 1999). Lowest quality aggregate deposits lie beneath alluvial fans, high-dissected terraces, and in paleovalley fills; except where composed of hard quartzite, this aggregate is not commonly of commercial value (Langer and Lindsey, 1999; Knepper and others, 2001).
Until the mid-1970s, petroleum production in the Front Range Urban Corridor was a fraction of present levels, being principally in rural areas largely removed from urban centers (Fishman and Roberts, 2001) and away from areas of significant production of aggregate resources. Although the land surface devoted to the production of petroleum at that time did not significantly interfere with aggregate production or with urban and commercial land uses, it did affect, at least locally, farming and grazing. Since the mid-1970s, however, increased exploration and production of petroleum resources has taken place largely within Adams, Boulder, and Weld Counties (fig. 1). Aggregate mining and urban expansion have also taken place in much of this same area (Arbogast and others, 2002). In some areas aggregate operations, urban development, and petroleum production have overlapped (Fishman and Roberts, 2001). Prediction of the degree to which overlap of competing land uses continues will be determined, in part, by the accuracy in projections of population growth, areas slated for urban expansion, and areas likely to see natural resource (oil, gas, and aggregate) development.
There are many facets to a more complete understanding of how petroleum and coal production has affected aggregate production and affected other land uses. In turn, petroleum production may be affected by aggregate mining or urban/commercial development. We have attempted to explore some of these facets in this paper. A summary of this work is presented herein, and details regarding the different data sets used in our analyses and also the methods used to quantify the effects of petroleum production are in the Appendix.
With thousands of producing petroleum wells in the GWA, it is not surprising to find many locations where wells drilled to petroleum reservoir rocks at depths of many thousands of feet also penetrate deposits of aggregate near the surface. Maps that were plotted after combining well location and aggregate deposit data (fig. 7) reveal that in the study area alone, 1,466 wells currently producing petroleum have penetrated aggregate deposits of various quality (table 1). Most wells that intersect aggregate deposits are in areas containing flood-plain or terrace deposits located along drainages including the Big Thompson River, Boulder Creek, Cache La Poudre River, Saint Vrain Creek, and South Platte River (fig. 7). Although these rivers and creeks flow through several counties, most of the wells that have been identified to intersect aggregate deposits do so in Weld County, with fewer wells penetrating aggregate deposits in northern Adams, eastern Boulder, and southeastern Larimer Counties (fig. 7).
Locations where petroleum wells were drilled through high- and medium-quality aggregate are of interest because these are the sites where aggregate mining is either currently underway or where, for economic reasons, aggregate is most likely to be mined in the future. A total of 675 wells, or 46 percent of the 1,466 petroleum wells that penetrated aggregate deposits, contacted aggregate of medium or high quality (table 1). Of those 675 wells, 516 (76 percent) penetrate high-quality aggregate deposits and 159 (24 percent) were drilled through medium-quality aggregate deposits (table 1). For the 516 wells drilled through high-quality aggregate deposits, 385 (about 75 percent) were drilled through flood-plain gravels, whereas 118 (about 23 percent) were drilled through terrace gravels (table 1); the remaining 13 wells (less than 3 percent) were drilled largely through other gravels. For those wells drilled through medium-quality aggregate deposits, 117 (about 74 percent) were drilled through terrace gravel and sand; the remaining 42 wells (26 percent) were drilled through either upland gravel and sand or flood-plain gravel and sand deposits (table 1).
Although this study focused on those locations where petroleum wells were drilled through medium- or high- quality aggregate deposits, a brief discussion of the wells drilled through low-quality aggregate deposits is included for completeness and also because we recognize that the value of an aggregate deposit can change as a result of changing economic conditions or increased market demand. Of the 1,466 petroleum wells drilled through aggregate deposits, 791 penetrated low-quality aggregate deposits composed of terrace sands (95 percent of the deposits) and valley-fill sand deposits (5 percent) (table 1).
The presence of petroleum-production infrastructure can affect the availability of aggregate resources where the two resources coexist, but the proportion of aggregate that is precluded from extraction (herein termed “sterilized”) as a result of petroleum production varies from site to site. Factors that ultimately determine the total area of land set aside for petroleum production include (1) the nature of the petroleum well (oil relative to gas) and whether a pump jack, which occupies more surface area than a gas wellhead, is necessary; (2) the presence and nature of additional production equipment onsite (for example, tank battery, separator, flow lines); (3) the length of the access road leading to the site; (4) the location of the access road; (5) setback requirements, outlined in local and State regulations to ensure safety, particularly along roadways and easements, and to promote and maintain stability of manmade structures; and (6) the location of pipelines and flowlines that carry petroleum and other produced fluids away from the well. If the thickness of an aggregate deposit is known, the volume of sterilized aggregate can be calculated for a given site.
A mined-out aggregate site on the Cache La Poudre River (fig. 7) is used to illustrate where the petroleum-production infrastructure has had a relatively minimal effect on the availability of aggregate resources. This site was chosen on the basis of field observations and information obtained from documents, mine plans, and mine/reclamation-plan permits filed with the Division of Minerals and Geology, State of Colorado. Some of the more significant reasons for choosing this site are the following: (1) the mine plan indicates that the gas wellhead is to be set back only 50 ft from the edge of the aggregate mine workings at the bottom of the pit; (2) the mine plan also indicates that the access road leading to the well head is 625 ft long and 100 ft across; (3) no additional production equipment is present on the land surface; and (4) the aggregate deposit underlying the site is relatively thin (about 20 ft). Calculations reveal that approximately 81,900 yd3 of aggregate has been sterilized at this site as a result of the petroleum-production infrastructure (see Appendix). Assuming that the aggregate weighs about 1.5 tons/yd3, then approximately 123,000 tons of aggregate was left in place to allow for production of natural gas. Based on the information available from the Division of Minerals and Geology, this volume of aggregate is approximately 5 percent of the total volume of aggregate present within the area permitted for mining at this site.
An active aggregate mine site on the South Platte River (fig. 7) is used to illustrate where the petroleum-production infrastructure has had an important effect on the availability of aggregate resources in an active mining operation. A review of documents and mine-plan information filed with the State of Colorado for this mine revealed that a much larger area of land has been committed for petroleum production equipment and facilities than at the site on the Cache La Poudre River. The South Platte River site (1) contains a variety of production equipment (tank battery and separator) as indicated from field observations, (2) includes a road designed to access the entire pad, and (3) is underlain by sand and gravel deposits ranging from 25 to 50 ft thick with an average thickness of about 35 ft. Calculations reveal that approximately 238,770 yd3 of aggregate will be sterilized by the petroleum-production infrastructure at this site (Appendix). Again assuming that the aggregate weighs about 1.5 tons/yd3, then about 358,000 tons of aggregate will be left in place as a result of petroleum production at this site. Based on the information available from the Division of Minerals and Geology, this volume of “lost” aggregate is approximately 4.35 percent of the total volume present within the area permitted for mining at this site.
The thousands of producing petroleum wells in the GWA along with the associated production infrastructure also limit use of the land directly underneath and also adjacent to the production infrastructure for additional purposes beyond the mining of aggregate. Utilizing geographic information system (GIS) technologies, the area of land used for petroleum production in relation to recognized land-use classification in the study area (see Appendix) was estimated. Minimum and maximum areas of land devoted to production equipment (pump jacks, wellheads, tank batteries) were calculated because of the large variability in total square footage devoted to the equipment that was noticed during field observations and measurements. In contrast, field observations revealed little variability in the width of access roads (about 10 ft), and because the total length of access roads was estimated by GIS techniques (see Appendix), it was possible to calculate the approximate total land area devoted to access roads. Thus, a single value is used herein for land area devoted to access roads rather than a minimum and maximum. Although setbacks and (or) easements exist around all well sites (in part to ensure ready access for well maintenance and repair), periodic use of the land within a given setback for purposes other than petroleum production is possible, as indicated from field observations and conversations with surface owners. Furthermore, although there are regulations defining the dimensions of a setback, negotiations between petroleum producers and surface owners can result in a decrease in these dimensions, so it is not possible to designate a uniform area to a setback around a well, and we did not do so in our calculations. Nevertheless, land within the setbacks may directly influence future aggregate or urban/commercial development.
A total of 7,035 actively producing petroleum wells exist within the study area that pump from one or more of the various producing formations. This number is large due to the relatively high density of wells within the GWA. A minimum of approximately 1,123 acres and a maximum of approximately 1,338 acres are devoted to the production infrastructure in the study area (table 2), most of which is devoted to access roads (table 2).
Approximately 69 percent of the surface area used for petroleum production in the study area is on land characterized as planted/cultivated, based on land-use land-classification maps (table 3); most of the remaining acreage is on land classified as natural herbaceous. Interestingly, energy-production equipment does indeed occupy a small area of land used for either urban or commercial purposes (table 3); however, rapid urban development and the drilling of many new wells in the past few years (subsequent to collection of the land-use data) in areas north of Denver have resulted in numerous examples of new urban development in close proximity to or surrounding production equipment (fig. 8).
Although emphasis in this study was placed on evaluating the effects of petroleum production on other land uses, petroleum production has, in turn, been affected by such land uses as aggregate production, urban development, and past coal mining. The presence of an aggregate mine, or a site that is now a lake or pond due to flooding of a former mine site, has necessitated moving several known petroleum well sites. Directional drilling (drilling at an angle rather than vertically) was required in order to access the available petroleum from the revised well location. Although the petroleum resources may still be acquired through directional drilling, the cost to drill and maintain a directional well is greater than a vertical well.
State of Colorado regulations for drilling in areas containing urban development have resulted in restrictions, at least locally, on petroleum exploration and development. In areas where there is high-density urban development, drilling for petroleum must be set back at least 350 ft from existing buildings or platted building sites (Colorado Oil and Gas Conservation Commission, 2003). Drilling setbacks from existing structures have been established largely for safety purposes, to protect people and property, and to protect the well-site infrastructure. Thus, even though petroleum producers might own or lease the mineral rights underlying an urban setting, setbacks prevent drilling at some locations. These setbacks may have a net effect of sterilizing some portion of the petroleum resources in the Front Range Urban Corridor.
Given the number of abandoned mines and the number of petroleum wells in the study area, it is not surprising to find places where wells were drilled through abandoned mine workings. A plot of well locations along with the extent of mine workings in the BWCF reveals that 231 wells have been drilled through abandoned workings. Most such wells are in Weld County, where there is a greater density of wells and numerous large abandoned mines. The degree to which past coal mining has affected petroleum production in ways other than the technological and safety challenges presented to petroleum companies when drilling through the voids of the abandoned workings was not determined.
More than 130 abandoned mines remain as evidence of the once bustling mining industry of the BWCF, a northeasterly trending group of mines that extend from southeastern Boulder County into Weld County (fig. 1). Although the areal extent of the workings of some of these mines is small (a few acres projected on the land surface), elsewhere, the areal extent of individual or multiple adjacent mines is quite large (hundreds of acres projected on the land surface). Any possible effects of past mining on aggregate availability or other land use would be largely confined to just those areas that are undermined or immediately adjacent to mined areas. Furthermore, there is likely to be a greater potential for an abandoned mine in the BWCF to affect the land surface where the workings are at shallow depths (less than 200 ft) (Myers and others, 1975; Roberts, this volume).
Few abandoned coal mines in the BWCF underlie aggregate deposits, regardless of aggregate quality (fig. 9). Thus, past coal mining will have little effect on potential extraction of aggregate within the undermined areas of the BWCF. In fact, only about 75 acres of land containing aggregate deposits of all qualities overlie abandoned coal mines (table 4), of which 51 acres (68 percent) contain aggregate deposits of medium or high quality. Of those 75 acres, about 36 acres (48 percent) containing aggregate deposits overlie abandoned mines that are less than 200 ft deep, whereas only about 3 acres (about 4 percent) containing aggregate deposits overlie mines that are less than 100 ft deep.
Approximately 1,730 acres of land throughout the BWCF is undermined by abandoned mines (table 5). Of the affected land, almost 62 percent (1,069.9 acres) is classified as planted/cultivated, about 20 percent (354.7 acres) is classified as natural herbaceous (table 5), and approximately 14 percent (246.1 acres) is classified as urban, commercial, or transportation (table 5).
Of the 1,730 acres of land overlying abandoned mines, 512.1 acres (about 30 percent) is undermined by shallow (less than 200 ft deep) mine workings; this includes 300.8 acres (59 percent) classified as planted/cultivated and 105.3 acres (about 21 percent) classified as natural herbaceous (table 5). Importantly, of the 512 acres undermined by shallow abandoned coal mines, a combined total of 90.9 acres (about 18 percent) is classified as either urban, commercial, or transportation (table 5).
Exploration and development of energy resources has led to aggregate sterilization, modification of land-use plans, and other consequences. On the other hand, production of both energy and aggregate resources also has had positive effects on the northern Front Range region. Because most of the extracted energy and aggregate resources are used locally, residents of the Front Range have benefited from the integration of these resources into local markets. In addition, the exploration and production industries have been a source of employment for many people in the region. Production of these resources has generated severance tax revenue, some of which has been returned for use by State and local governments.
Numerous factors may ultimately influence the degree to which production of energy resources affects availability of aggregate resources, development, or other land uses. Factors related to energy production that may have significant effects on land use include the following: (1) producing wells in areas of current aggregate mining or areas containing economic deposits of aggregate; (2) producing wells in areas of current urban/commercial development or areas planned for development; (3) areas of potential future petroleum production; (4) the successful application of advanced petroleum recovery technology, which can extend the production life of wells; and (5) the amount of surface disruption due to subsidence that has occurred above abandoned coal mines. In contrast, factors related to energy production that exert minimal effects on land use, particularly in the future, include (1) plugging and abandoning existing wells prior to aggregate mining, (2) plugging and abandoning existing wells prior to urban/commercial development, and (3) mining coal at levels that were sufficiently deep to minimize the threat of associated subsidence.
Some of these listed factors are economically controlled, which indicates that a change in economic conditions can potentially affect the significance of one or more factors. For example, a rise in oil or gas prices may encourage continued petroleum production from an otherwise subeconomic well or perhaps the drilling of a new well, whereas a drop in prices might force abandonment of a well earlier than expected. The effects of coal production on land use is substantially reduced or may be removed entirely once production ceases, with the possible exception of subsided ground above shallow or otherwise unstable mined-out areas.
Quantifying the long-term effects of energy production on land use across the study area is difficult because changing economic conditions, technology, demand, and public opinion can all individually or collectively affect future decisionmaking. Nevertheless, it is possible to place some of the effects of petroleum production on other land uses into a context to illustrate local effects. As an example, we compared the volume of aggregate sterilized by petroleum production in the two examples given earlier in this chapter to the total volume of aggregate produced in the State of Colorado for 1999, the last year for which such data are available. For the site along the Cache La Poudre River, the approximately 123,000 tons of aggregate sterilized by the petroleum production infrastructure represents only a small fraction of the more than 45,200,000 tons of aggregate produced in Colorado in 1999 (annual production data from Bohlen, 1999). For the site along the South Platte River, the approximately 358,000 tons of aggregate sterilized by the petroleum production infrastructure represents less than 1 percent of the aggregate produced in Colorado in 1999. It is likely, however, that the aggregate sterilized by petroleum production will be permanently removed from the resource base of aggregate because it would be very expensive, at a later date, to mine the aggregate left behind.
The volume of aggregate sterilized at a given site by petroleum production may, however, represent a large portion of the total volume of aggregate available for mining at that location. At the Cache La Poudre site, the approximately 123,000 tons of aggregate sterilized by the petroleum production infrastructure represents about 5 percent of the aggregate that could have been mined at that site. At $8.15 and $4.86 per metric ton, the average prices for graded coarse and fine aggregate produced in Colorado in 2000 (U.S. Geological Survey, 2000), respectively, the aggregate sterilized at the Cache La Poudre site would have a gross value of approximately $672,000 (Appendix), if sold in that year. At the South Platte River site, the approximately 358,000 tons of aggregate sterilized by the petroleum-production infrastructure represents about 4.35 percent of the aggregate resource at that site. Again, using the average prices for graded aggregate produced in Colorado in 2000 (U.S. Geological Survey, 2000), the aggregate sterilized at the South Platte River site would have a gross value of approximately $1,959,000, again assuming all would have been sold during 2000. The effects of petroleum production on aggregate availability may increase if aggregate producers continue to move downstream, particularly along the South Platte River, into areas containing not only unmined aggregate resources but also a greater density of existing petroleum wells. This downstream area along the South Platte River also has a relatively high potential for additional exploration for petroleum (Cook, this volume), which may increase the potential for future sterilization of aggregate resources by petroleum production unless the production had already ended.
The effects of coal mining in the BWCF are largely a function of the hazards associated with the abandoned mines. Although much of the surface evidence of coal mining, such as mine buildings, rail lines, and tipple and loadout sites, has been removed, hazards related to subsidence and mine fires remain. Open underground rooms in mine workings are still present, leaving the possibility of additional collapse and subsidence. How much of the additional land surface may be affected by future coal-mine-related subsidence cannot be determined, but it is unlikely such subsidence would significantly affect aggregate production in the northern Front Range inasmuch as abandoned coal mines underlie few areas containing aggregate deposits (see fig. 9).
Fires have occurred in mines throughout much of the mining history of the BWCF (Roberts and others, 2001) and have been documented as recently as 1988 in some abandoned mines (Rushworth and others, 1989). The fires started either spontaneously or were ignited by human activity (Myers and others, 1975; Herring and others, 1986). Because these fires burn whatever coal remains in the mines, including that in supporting pillars, they can lead to collapse and surface subsidence long after mine abandonment (Myers and others, 1975; Herring and others, 1986). Airborne magnetic surveys are useful in detecting highly magnetic rocks that form as a result of fires in abandoned coal mines (Rodriguez, 1983), so areas susceptible to fire-related subsidence in the BWCF may be identified by geophysical methods. A recent magnetic survey of limited areal extent not only detected highly magnetized rock associated with a known mine fire, but identified similarly magnetized rock in areas where mine fires were not known to have existed, at least while the mine was in operation (Fishman and others, 2001). Thus, fire-related subsidence may continue to be of concern in some areas of the BWCF into the foreseeable future.
Conflicts arising from resource development in the northern Front Range of Colorado can be intense and complex in nature. Examples were presented in foregoing sections to illustrate cases where development of energy resources has sterilized aggregate resources and, conversely, where petroleum production is affected by alternate land uses. Although concerted efforts have been made in recent years to mitigate conflicts between various parties, much more planning on a regional scale could be done to further minimize conflicts well into the future.
Land-use conflicts between energy and aggregate producers are not new, but novel approaches to potential resolutions have been implemented to the benefit of both industries, ultimately benefiting the consumer as well. Some relatively straightforward solutions have included moving components of the petroleum-production infrastructure such as pipelines, flow lines, access roads, and tank batteries to minimize aggregate sterilization without compromising petroleum production. Although setting aside a site to house production equipment for multiple petroleum wells may indeed sterilize a significant volume of aggregate under that site, several smaller, individual well sites that would be necessary instead of a large multiwell site may serve to sterilize an even greater volume of aggregate. Overall, the loss in total aggregate production due to petroleum production would be less with a single, larger well site.
Significant quantities of petroleum remain in the ground for exploitation in the northern Front Range Urban Corridor (Higley and Cox, this volume; Cook, this volume) even though urban expansion is placing petroleum production in direct land-use competition. Although petroleum producers, as owners or lessees of the mineral estate, have legal access to the land surface to pursue exploitation of petroleum resources, existing regulations prevent or limit exploration and production activity where urban/commercial development has already occurred. Furthermore, some wells in developed areas are being abandoned for various economic or political reasons. Thus, urban development has led to sterilization of some portion, albeit possibly small, of the petroleum resource base.
In an attempt to minimize litigation, energy-production companies are working more closely with developers to reduce the number and severity of surface-use conflicts between petroleum production and urban growth. One solution is to allow petroleum producers to site and drill wells prior to the start of urban development. Another solution is to set aside a location from which multiple wells, drilled vertically or directionally, can be placed to minimize the number of drill sites in or near urban development. An additional solution is to relocate pipelines, access roads, and production facilities to sites where the effects on surface development are minimized. All of these solutions involve consideration from a developer in return for the energy-producing company’s relinquishment of the right to access specific areas.
Because much of the land surface in the study area is planted/cultivated, conflicts between petroleum producers and farmers are inevitable. Some have been mitigated effectively, however, through constructive communication between producers and farmers. The intentional positioning of well sites outside the perimeter of a center-pivot irrigation system provides a good example of how effective communication allowed a petroleum producer to gain access to the land surface for exploration and production of oil without interfering with the irrigation system. Active communication also has resulted in construction of low-profile production facilities specifically designed to allow for irrigation equipment to pass over the top of the petroleum-production infrastructure. Another tool used to minimize conflict is to schedule well drilling and maintenance so as not to coincide with planting, irrigating, and harvesting activities, which minimizes losses to the farmer without serious consequences to the petroleum producer.
Past efforts to mitigate conflicts may not always work in the future. Nevertheless, petroleum-production companies are finding it beneficial to work more closely with governmental planners, aggregate-production companies, developers, and farmers to minimize conflict and promote good relations. As urban expansion continues in the northern Front Range of Colorado, the availability of resources needed to build and sustain urban areas will be further challenged. Thus, the quality of life for residents of the Front Range depends on balancing competing interests through wise decisionmaking.
Oil, natural gas, and coal have been produced for more than 100 years from subsurface deposits across much of the area underlying the plains immediately adjacent to the northern Front Range of Colorado. More than 7,000 petroleum wells and some 130 abandoned coal mines are in the area of this study, which includes parts of Adams, Boulder, Denver, Larimer, and Weld Counties in eastern Colorado. Because energy producers are legally afforded access to the land surface to search for and produce resources, regardless of who owns the land surface, production of energy resources can limit use of the land for other purposes including production of aggregate resources, development of urban and commercial buildings, and farming.
Energy production has had a direct effect on the production of aggregate resources in the region. At one study site, approximately 123,000 tons of aggregate was precluded from production as a result of the production of energy resources, whereas at a second site approximately 358,000 tons of aggregate will remain unmined due to energy production. These amounts are individually less than 1 percent of the total output of aggregate from Colorado in 1999. Nevertheless, the approximately 123,000 tons of sterilized aggregate at the one site is about 5 percent of the total volume of aggregate present in that mine area and would have a gross value, at average prices for the year 2000, of about $672,000. The approximately 358,000 tons of aggregate sterilized at a second site represents about 4.35 percent of the total volume of aggregate present there and would be worth, at average prices for the year 2000, about $1,959,000. Thus, at both sites, the petroleum-production infrastructure sterilizes an appreciable amount of aggregate.
Energy production also has affected use of the land surface throughout the study area. The energy-production infrastructure, exclusive of setbacks, potentially may consume as much as 1,300 acres of land surface across the region, much of which is devoted to access roads leading to well sites. Although most of this land area is classified as planted/cultivated, an increasing amount of energy is being produced on land that is classified as urban or commercial.
Past coal mining has left behind an abundance of coal-mine workings, some of which present hazards to uses of the overlying land surface. Subsidence of the land surface, caused by the collapse of abandoned underground mines, precludes most options for land use because of the unstable nature of the subsided ground. Subsidence is most likely to affect land use where the mine workings are at relatively shallow depths; only about 28 percent of the land surface over all the mine workings in the BWCF overlies these relatively shallow mines, and most of that land is classified as planted/cultivated. Although the potential effects of subsidence on urban development are not large, this risk should not be overlooked. Coal-mine fires, some of which have been burning in recent years, are troublesome because they may burn the coal in pillars left behind, causing the workings to collapse. Such surface subsidence from coal-mine collapse presents challenges when planning for future land use.
Perhaps most important are the efforts being made to mitigate conflict between those competing for use of the land. Petroleum-production companies are finding it increasingly beneficial to work closely with governmental planners, aggregate-production companies, developers, and farmers to minimize problems and promote good relations. Expanded efforts toward mutually acceptable solutions will go far in promoting wise, well-reasoned decisions for future uses of the land.
The authors are grateful to Dave Lindsey, Tim Rohrbacher, William Keefer, and Mary Kidd for their comprehensive and constructive reviews. We also thank the coordinators of the Energy Resources and Mineral Resources Program of the U.S. Geological Survey for allowing us to pursue this investigation.
Base cartographic data used in this study were from digital files obtained from colleagues at the U.S. Geological Survey; the data are available as downloadable files from http://rockyweb.cr.usgs.gov/frontrange/datasets.htm. These files include political boundaries, hydrography, public land survey system, roads, and miscellaneous transportation. Each of the data sets were projected with the following parameters: Projection, Universal Transverse Mercator (UTM); Zone, 13; Units, meters; Datum, NAD 83; and Spheroid, GRS 1980. Detailed metadata are found at the Web site.
Well locations were obtained from digital files available from the Colorado Oil and Gas Conservation Commission (Colorado Oil and Gas Conservation Commission, 2001). Well locations were determined digitally by using an automated program that converts locations from the Commission’s analogue database to UTM Zone 13 (NAD 27) coordinate values. If precise locations were uncertain, then the well coordinates were calculated to be at the center of a quarter-quarter section. The well location file was created at a scale of 1:24,000 (Colorado Oil and Gas Conservation Commission, 2001). Although detailed information concerning the type of petroleum produced from individual wells (oil or gas, and so forth) and producing formation was obtained from proprietary files (IHS Corporation, 2001), these data were used only for informational and analytical purposes and not for displaying well locations.
Field observations and geographic information system (GIS) investigations were used to identify sites where aggregate operations occur along with petroleum production. Visiting 13 sites allowed for selection of two that seemed to represent end members in terms of the volume of aggregate that might be sterilized by petroleum production. The
locations of the two sites were identified from topographic maps, which then allowed for determination of the mine names and locator information in files at the Division of Minerals and Geology, State of Colorado. The files, which are of public record, were used to identify the shape and dimensions of the areas set aside for petroleum production in both mines. Other information obtained from these files included the total area expected to be mined, the thickness of the aggregate deposits at both mine sites, and the nature of the mining operations, which in turn served to constrain our calculations of aggregate resources sterilized by petroleum production.
For the aggregate operation on the Cache La Poudre River (see text fig. 7), the mine-plan files reveal that the land overlying the aggregate deposit that was set aside for petroleum production is elongate in shape, with the pad around the gas well at one end. The plans filed with the Division of Minerals and Geology reveal that the access road, under which is the gas pipeline leading from the well, is 100 ft wide. A slope with a ratio of 3:1 (three horizontal feet for one vertical foot) was used to determine the shape and dimension of the apron along each side of the access road and around the well pad, based on documents filed with the Division of Minerals and Geology. Information regarding the thickness of the aggregate deposit, also in files at the Division of Minerals and Geology, allowed us to calculate the volume of aggregate sterilized by the production infrastructure at this site (fig. A1). Conversion of volumetric calculations from cubic yards to tons was desired because most reports of aggregate production are presented in terms of tons. The gross value of aggregate sterilized by the petroleum production infrastructure was calculated assuming that 35 percent of the volume of the aggregate at the site was coarse aggregate with a value of $8.15/metric ton, and the remaining 65 percent of the aggregate was assumed to be fine sand with a value of $4.86/metric ton.
For the aggregate operation on the South Platte River (text fig. 7), the area of land overlying the aggregate deposit that was set aside for petroleum production is irregular in shape (fig. A2), as indicated in drawings included in the files at the Division of Minerals and Geology, State of Colorado. Due to the irregular shape of the site, calculations of the volume of aggregate under the petroleum-production infrastructure required multiple steps. For convenience, this petroleum-production infrastructure site was broken into numerous triangular or rectangular segments to allow for calculation of the volume of aggregate sterilized. Although this method introduced error into the calculations, the magnitude of the error is considered minimal because subdividing the area this way closely approximated the entire site. Information regarding the thickness of the mined deposit, also found in the files from the Division of Minerals and Geology, allowed us to calculate the volume of aggregate sterilized by the production infrastructure at this site. An excavation slope with a ratio of 0.5:1 (one-half foot horizontal for one vertical foot) was used to determine the shape and dimension of the apron along the perimeter of part of the site (fig. A2), whereas a slope with a ratio of 3:1 (three horizontal feet for 1 vertical foot) was used to determine the shape and dimension of the remaining apron at the site (fig. A2). The slope ratios were determined from documents filed with the Division of Minerals and Geology.
For the utility easement through the aggregate operation on the South Platte River (fig. A2), the easement devoted to each of the parts of the three utility poles that extend beyond the utility access road was estimated to be equivalent to a single, circular cone. Thus, the volume of aggregate sterilized by the utility poles that extended beyond the access road was calculated using the frustrum for right circular cone formula.
For all calculations, a conversion factor of 1.5 tons per cubic yard was used to determine the total tonnage of aggregate sterilized at the site along the South Platte River. The gross value of aggregate sterilized by the petroleum- production infrastructure was calculated assuming that 35 percent of the aggregate at the site was coarse aggregate, with a value of $8.15/metric ton, and the remaining 65 percent of the aggregate was assumed to be fine sand with a value of $4.86/metric ton.
Field observations and measurements, as well as GIS investigations, were useful in estimating the land area that is devoted to petroleum production. It is important to note that, for this study, the land area devoted specifically to the production infrastructure was estimated and did not include setbacks or easements. Setbacks and easements were not included because some of the land with an easement, particularly in agricultural areas, can continue to be used for purposes other than petroleum production. Only during times of well maintenance is land within setbacks used by the producer. Field observations and measurements were used to determine a range in total area of land that may be devoted to production equipment, including pump jacks, wellheads, tank batteries, and access roads (see text fig. 3). The field measurements were then used to calculate the variations in land area that production equipment may occupy at individual sites throughout the study area. It was then possible to calculate minimum and maximum areas devoted to the production equipment. In general, a pump jack is needed to produce oil and associated water from the Terry Sandstone Member of the Pierre Shale and the Lyons Sandstone. Field measurements revealed a minimum area (1,000 ft2) and maximum area (4,500 ft2) devoted to such pump jacks. Of the well sites visited (n=21), about one-half occupied a large (maximum) area of land, whereas the remainder occupied a small (minimum) area of land. Because there are more than 1,100 wells that produce from these formations, it was impractical to visit all wells to evaluate the actual area occupied at each. Thus, we arbitrarily assigned one-half of them a maximum land area and the remainder a minimum land area for the purposes of calculating total land area devoted to production from these wells. As such, errors were introduced into the calculations of the land area devoted to this production equipment, so the figures presented herein should be viewed only as an approximation of the land area devoted to petroleum production.
Calculations performed to determine the area of land devoted to oil, oil and gas, or gas wells requiring production equipment other than a pump jack required some assumptions as well. Wells that do not require a pump jack occupy less area than wells that do require a pump jack. Again, field observations and measurements were used to establish the range in areas occupied by this equipment. Field measurements (n=16) revealed a minimum (110 ft2) and maximum (1,000 ft2) area devoted to such wellheads and that about one-half the well sites occupied a large (maximum) area of land whereas the remainder occupied a small (minimum) area of land. In the absence of any observable systematic distribution in the area of land devoted to smaller pumping equipment, we arbitrarily assigned one-half of these wells a maximum value of land area and the remaining wells a minimum value of land area occupied by this production equipment. Errors introduced into the calculations of the land area devoted to this production equipment are likely, so the results should be viewed as only an approximation.
Access roads were measured onsite (n=10) to determine their width and length. Although the length of these roads was highly variable, their width was more consistent, based on our observations and measurements. We used a 10-ft width for all access roads when calculating the total land area devoted to these features. The length of roads was measured or estimated from digital base cartographic data, depending on the availability of data. Where well sites were known but no access road was observed in the digital files, we estimated the length of the road by plotting a straight line from the well to the closest known road. Although this may have introduced errors into our calculations, it is likely that most access roads are designed to traverse the shortest route from an established county or municipal road to reduce construction costs. Thus, we feel that our estimations are not seriously in error.
Once the dimensions of the production infrastructure were established and assigned to all wells in the study area, it was possible not only to calculate the land area occupied by the infrastructure but also to assign total area of land occupied as a function of land-use land-cover (LULC) (see text table 3). The LULC data, which are now publicly available as digital layers through the USGS Web site (http://rockyweb.cr.usgs.gov/frontrange/datasets.htm), were provided by USGS staff studying these features in the Front Range. The LULC data have been projected with the following parameters: Projection, Universal Transverse Mercator (UTM); Zone, 13; Units, meters; Datum, NAD 83; and Spheroid, GRS 1980. The LULC data were produced from high-resolution imagery acquired in 1997. Although the land-classification scheme used was based on that published by Anderson and others (1976), the scheme represents a modification of their work (Carol Mladinich, U.S. Geological Survey, oral commun., 2002) because land classifications were broken into greater detail than was originally done by Anderson and others (1976). Detailed explanation of the LULC scheme used for our study can be found at this Web site.
Boulder-Weld Coal Field (BWCF) The geographic area in which coal was produced in Boulder and Weld Counties from the Laramie Formation from the late 1850’s through the 1970’s.
Frustrum A portion of a cone that is formed by cutting off the top by a plane parallel to the base.
Greater Wattenberg area (GWA) A geographic area defined by the Colorado Oil and Gas Conservation Commission for oil and gas regulatory purposes, especially as it pertains to oil and gas production from formations of Cretaceous age. The south and north boundaries are Townships 2 South and 7 North, respectively, and the east and west boundaries are Ranges 61 West and 69 West, respectively. All are relative to the Sixth Prime Meridian.
High density (pertaining to oil and gas set-back requirements) An area, determined when an oil or gas well is permitted, where thirty-six (36) or more actual or platted building units are within 1,000-foot radius or 18 or more building units are within any semicircle of the 1,000-foot radius from the wellhead or production facility.
Land use land cover (LULC) Categorization of land features at a minimum area of 2.5 acres from remotely sensed data. Categories were initially defined by Anderson and others (1976) and have since been modified to include more category levels including urban parks, natural grasslands, major retail, light industry, and row crops.
Mineral estate Refers to an interest in real property, as shown by real estate records, that is not owned as the full fee heading2 to the real property. The owner or lessee of the mineral estate has rights to the valuable subsurface substances. The rights afforded the owner or lessee of the mineral estate are commonly referred to as mineral rights.
Set-back requirements from manmade structures As per Colorado law, at the time of drilling a petroleum well, the wellhead must be 150 feet away from any manmade structure, or 350 feet in an area of high density (see above definition for high density).
Surface estate Refers to an interest in real property that is less than full fee heading2 and does not include the mineral estate as shown by real estate records. The rights afforded the owner or lessee of the surface estate are commonly referred to as surface rights.
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