Review of Well Logging in the Basin and Range Known Geothermal Resource Areas
Summary
This paper discusses applications and interpretations of well logs to Basin and Range Province geothermal exploration and development. Problems experienced in use of conventional oilfield tools and techniques are reviewed, and methods to circumvent these problems are illustrated. Particular examples focus on log responses and matrix effects in complex lithologies.
Introduction
In 1977, the U.S. DOE's Div. of Geothermal Energy (DGE) initiated the "industry coupled program" to accelerate development of high-temperature geothermal resources. There are two key aspects of the program:cost sharing with industry for exploration, reservoir assessment, and reservoir confirmation, andthe release of geologic, geophysical, and geochemical data to improve knowledge and understanding of geothermal reservoirs.
A third aspect of the program was to evaluate techniques and current methods on a cost-effective basis. Two regions of high industry interest and high geothermal potential were selected by DGE for procurements within the industry coupled program. The first request for proposals (RFP) resulted in six contracts for work in south central Utah, the second in 12 contracts for exploration and reservoir assessment work in the northern Basin and Range Province. The geothermal resource areas included in the program are shown in Fig. 1. The range of exploration activities of participating companies and data to be made public through this program are indicated in Table 1. Ward et al. studied these data and recommended a generalized exploration strategy for high-temperature geothermal systems in the Basin and Range Province. Fiore provided an overview and status report for the overall reservoir assessment program. The program's emphasis was direct drilltesting of the geothermal reservoir. At least one deep exploration well has been (or will be) drilled in each reservoir, at costs between $500,000 and $2,000,000. The high well costs demand prudent, systematic exploration before siting the well and as much geologic information as possible from each well test. Drill cuttings, geophysical well logs, temperature, pressure and flow test data, and complete well histories for each well drilled are transmitted to the U. of Utah Research Inst's. Earth Science Laboratory Div. (ESL). ESL reviews and approves the deliverables and makes data available to the public through established open-file procedures. Geophysical well logs are transmitted to Rocky Mountain Well Log Services (of Petroleum Information Corp.), where they are reproduced and distributed at nominal cost. In this manner detailed well data for 29 geothermal exploration wells and deep thermal gradient tests have been made public since 1977. The current status of drilling and the availability of well log data are listed in Table 2. Many thermal gradient holes with only mud and temperature logs are not included in Table 2. Note that DGE has instituted complementary and supporting programs designed to advance well log interpretation and high-temperature tool development. At ESL detailed well log/lithologic interpretations form an important part of several reservoir case histories and topical studies published or in preparation. These integrated interpretations are instrumental to the planning of subsequent well tests and to overall reservoir evaluation. We describe well log data that have been made available through the industry coupled program. Logging parameters used, data quality, previously published log interpretations, and some results of the ESL log interpretation work are reviewed and discussed.
Well Logging in Geothermal Areas
JPT
P. 1104^
