U.S. DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY
The Santa Cruz - Tarija Province of Central South America: Los Monos - Machareti(!) Petroleum System¹
by
Sandra J. Lindquist ²
Open-File Report 99-50-C
| This report is preliminary and has not been reviewed for conformity with the U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. government. |
1998
|
The entire Open-File Report 99-50-C can be successfully viewed or downloaded (1.6MB), for use with Adobe Acrobat Reader (version 3.0 or later). If you do not already have Acrobat Reader version 3.0 or later, you may download the latest version here. FOREWORD FIGURES 1. Chart of stratigraphic
equivalents for Santa Cruz - Tarja province TABLES 1. Santa Cruz - Tarija province production and reservoir statistics This report is a product of the World Energy Project of the U.S. Geological Survey, in which the world has been divided into 8 regions and 937 geologic provinces for purposes of assessment of global oil and gas resources (Klett and others, 1997). These provinces have been ranked according to the discovered petroleum volumes within each; 76 "priority" provinces (exclusive of the U.S. and chosen for their high ranking) and 26 "boutique" provinces (exclusive of the U.S. and chosen for various reasons) were selected for appraisal of oil and gas resources. The petroleum geology of these non-U.S. priority and boutique provinces is described in this series of reports. Assessment results will be released in a later report, if such results are not reported herein. The Total Petroleum System concept is the basis for this assessment. A total petroleum system includes the essential elements and processes, as well as all genetically related hydrocarbons, that occur in petroleum shows, seeps and accumulations (discovered and undiscovered), whose provenance is a pod or closely related pods of mature source rock (concept modified from Magoon and Dow, 1994). The minimum petroleum system is that portion of the total petroleum system for which the presence of essential elements and processes has been proved. The assessment unit is a mappable volume of rock within the total petroleum system, sufficiently homogeneous in terms of geology, exploration strategy and risk characteristics to constitute a single population with respect to criteria used for the chosen methodology of resource assessment. Assessment units are considered established if they contain more than 13 fields, frontier if they contain 1-13 fields, and hypothetical if they contain no fields. A unique, eight-digit numeric code identifies each assessment
unit with respect to region, province, and petroleum system. The first
digit is the region number, the next three digits the province number,
the next two digits the total petroleum system number, and the final two
digits the assessment unit number. The codes for the regions and provinces
were established, listed and mapped in Klett and others, 1997. The Los Monos – Machareti(!) total petroleum system is in the Santa Cruz – Tarija Province of Bolivia, Argentina and Paraguay. Province history is that of a Paleozoic, intracratonic, siliciclastic rift basin that evolved into a Miocene (Andean) foreland fold and thrust belt. Existing fields are typified by alternating reservoir and seal rocks in post-Ordovician sandstones and shales on anticlines. Thick Devonian and Silurian shale source rocks, depositionally and erosionally confined to this province, at a minimum have generated 4.1 BBOE known ultimate recoverable reserves (as of 1995, 77% gas, 15% condensate, 8% oil) into dominantly Carboniferous reservoirs with average 20% porosity and 156 md permeability. Major detachment surfaces within the source rocks contributed to the thin-skinned and laterally continuous nature of the deformation. Tertiary foreland burial adequate for significant source maturation coincided with the formation of compressional traps. Further hydrocarbon discovery in the fold and thrust belt is expected. In the foreland basin, higher thermal gradients and variable burial history – combined with the presence of unconformity and onlap wedges – create potential there for stratigraphic traps and pre-Andean, block-fault and forced-fold traps. The Santa Cruz – Tarija Province of Bolivia, Argentina and Paraguay is named for two larger cities that approximately define its north-south geographic limits within the eastern Andean region of central South America. The term Chaco-Tarija used throughout this report denotes the evolved Paleozoic-to-Recent Bolivian-Paraguayan basin that covers most of the province and also extends farther northwest into Peru. This Chaco-Tarija basin should not be confused with a similar terminology, the Chaco-Parana basin, which is to the south and east in Argentina. One petroleum system, Los Monos – Machareti(!), with Siluro-Devonian shale source rocks and Carboniferous siliciclastic reservoirs (Figure 1), dominates this foreland fold and thrust belt. Primary Devonian Los Monos and secondary Silurian Kirusillas / El Carmen shales attain a maximum 4-km composite thickness and have type II to type III kerogen with maximum 2 wt % total organic carbon (TOC). Other significant reservoirs are Devonian (especially in the northwestern part of the province), with lesser Tertiary, Cretaceous, Permo-Triassic and Silurian representation as reservoir rocks. There are oil shows in Cambrian and older rocks along the northeastern edge of the province that could belong to source rocks older than Siluro-Devonian. A book (A.A.P.G. Memoir 62) published jointly by the American Association of Petroleum Geologists, Yacimientos Petroliferos Fiscales Bolivianos, and Academia Nacional de Ciencias de Bolivia (Tankard and others, 1995) contains recent syntheses of South American geology and is referenced extensively here. Quantitative production data are derived from Petroconsultants (1996). The stratigraphic equivalents chart in this report (Figure 1) is composited from many references to approximately equate the range of stratigraphic nomenclature in use. It is not intended to be precise with respect to absolute geologic age. _____________________ ² Sandra J. Lindquist,
Consulting Geologist Contractor to U.S. Geological Survey, Denver, CO |
U.S. Geological Survey Open-File Report 99-50-C
