Preliminary Compilation of Data for Selected Oil Test Wells in Northern California

Introduction

Oil test wells can provide information on the depth, age, inclination, porosity, permeability, density, faulting, folding, and organic content of geologic formations mapped at the surface, or on units not recognized in surface outcrops. Formation density, as expressed in sonic and density logs commonly obtained when wells are drilled, has become increasingly important in making a crustal-scale 3-D seismic velocity model for the San Francisco Bay region. This model will be used for the calculation of realistic strong-ground motion synthetic seismograms (Brocher and others, 1997), and to determine the geometry of the basement surface beneath Tertiary basins (Jachens and others, 1997). The availability of this density and other information for oil test wells has, until recently, been restricted for competitive reasons, but several petroleum companies have recently made these data available. Accordingly, we began in 1992 to obtain these data to help prepare new geologic maps and geophysical models for the San Francisco Bay region, and to share the information with the public.

This report contains brief descriptions of information and materials available for 1,550 oil exploration and production wells in the following counties: Alameda (42), Butte (31), Colusa (103), Contra Costa (102), Glenn (103), Humboldt (33), Marin (6), Mendocino (2), Merced (33), Monterey (172), Napa (5), Placer (2), Sacramento (72), San Benito (51), San Joaquin (164), San Mateo (73), Santa Clara (8), Santa Cruz (23), Shasta (3), Siskiyou (1), Solano (251), Sonoma (10), Stanislaus (29), Sutter (59), Tehama (59), and Yolo (113).

First posted June 11, 2001