14 research outputs found
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Formation evaluation in liquid-dominated geothermal reservoirs
Studies relative to some formation evaluation aspects of geothermal reservoirs are reported. The particular reservoirs considered were the liquid dominated type with a lithology of the sedimentary nature. Specific problems of interest included the resistivity behavior of brines and rocks at elevated temperatures and studies on the feasibility of using the well log resistivity data to obtain estimates of reservoir permeability. Several papers summarizing the results of these studies were presented at various technical meetings for rapid dissemination of the results to potential users. These papers together with a summary of data most recently generated are included. A brief review of the research findings precedes the technical papers. Separate abstracts were prepared for four papers. Five papers were abstracted previously for EDB
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Well Log Interpretation of the Cerro Prieto Field
To examine how changes in rock properties affect the well log responses in a sedimentary type geothermal field, we studied the well logs from the Cerro Prieto field in Mexico. A fair amount of well logs are available for the field. Copies of the logs were obtained through the Lawrence Berkeley Laboratory
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Well log interpretation of certain geothermal fields in the Imperial Valley, California
This study reviews the wireline log responses of some geothermal fields in the Imperial Valley, California. The fields under study include the Heber, the East Mesa, the Brawley, and the Westmoreland. The well logs used in the study did not include all the wireline surveys obtained by the operators. The selected well logs obtained under special arrangements with the operators were chosen to maintain the anonymity of specific well locations but are only representative of each area. Analysis of the well logs indicates that on an individual field basis, the well logs are excellent for correlation purposes. The presence of extremely saline fluids in some fields precludes the monitoring of Q/sub v/ (cation exchange capacity per unit volume) profile for detection of hydrothermally altered zones. The producing sections in all the fields are characterized by low porosity and high resistivity
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Lithology and hydrothermal alteration determination from well logs for the Cerro Prieto Wells, Mexico
The purpose of this study is to examine the characteristics of geophysical well logs against the sand-shale series of the sedimentary column of the Cerro Prieto Geothermal Field, Mexico. The study shows that the changes in mineralogy of the rocks because of hydrothermal alteration are not easily detectable on the existing logs. However, if the behavior of clay minerals alone is monitored, the onset of the hydrothermally altered zones may be estimated from the well logs. The effective concentration of clay-exchange cations, Q/sub v/, is computed using the data available from conventional well logs. Zones indicating the disappearance of low-temperature clays are considered hydrothermally altered formations with moderate to high-permeability and temperature, and suitable for completion purposes
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Fractal analysis of pressure transients in the Geysers Geothermal Field
The conventionally accepted models for the interpretation of pressure transient tests in naturally fractured reservoirs usually involve simplistic assumptions regarding the geometry and transport properties of the fractured medium. Many single well tests in this type of reservoirs fail to show the predicted behavior for dual or triple porosity or permeability systems and cannot be explained by these models. This paper describes the application of a new model based on a fractal interpretation of the fractured medium. The approach, discussed elsewhere [2], [6], is applied to field data from The Geysers Geothermal Field. The objective is to present an alternative interpretation to well tests that characterizes the fractured medium in a manner more consistent with other field evidence. The novel insight gained from fractal geometry allows the identification of important characteristics of the fracture structure that feeds a particular well. Some simple models are also presented that match the field transient results
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Fracture patterns in graywacke outcrops at The Geysers geothermal field
The Geysers geothermal field covers an area of more than 35,000 acres and represents one of the most significant steam fields in the world. The heterogeneous nature of the reservoir, its fracture network and non-sedimentary rock distinguish it from ordinary sandstone reservoirs in terms of reservoir definition and evaluation (Stockton et al. 1984). Analysis of cuttings, record of steam entries, temperature and pressure surveys and spinner logs have contributed to an understanding of the subsurface geology and rock characteristics of the Geysers. Few conventional electrical log data are available for the main body of the reservoir. It is generally believed that while the fractures are the main conducts for fluid transport through the reservoirs, tight rocks between the major fractures contain the bulk of the fluid reserves. No independent measurement of liquid and vapor saturation can be made from the existing downhole tools. Pressure depletion in The Geysers geothermal field has become a major concern to the operators and utility companies in recent years. Plans for further development activities and future field management are contingent upon accurate computer modeling and definition of the field. The primary issues in reliable characterization of The Geysers field are the role of the rock matrix in holding liquid reserves and providing pressure support, the nature of fracture network, extent of liquid saturation in the reservoirs and injection pattern strategies to maximize heat recovery. Current modeling of The Geysers field is done through the use of general purpose geothermal reservoir simulators. Approaches employed include treating the reservoir as a single porosity equivalent or a dual porosity system. These simulators include formulation to represent transport of heat, steam and water. Heterogeneities are represented by spatial variations in formation or fracture permeability-thickness product, porosity or fluid saturations. Conceptual models based on dual porosity representations have been shown to duplicate the history. Prediction of future performance is, however, not reliable because of uncertainties in assumptions of the initial state of the reservoir, Specifically, several different initial state conditions have led to a fairly good match of the historical data. Selection of the exact initial conditions is a major dilemma. In dual porosity models, the complex nature of fracture network is formulated by a systematic, well-organized set of orthogonal fractures. Also, the exact nature of matrix-fracture interaction, and the role of adsorption and capillarity in pressure support are not well-defined
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Increasing heavy oil reserves in the Wilmington oil field through advanced reservoir characterization and thermal production technologies. Quarterly technical progress report, March 30, 1995--June 30, 1995
This is the first quarterly technical progress report for the project. Although the contract was awarded on March 30, 1995 and Pre-Award Approval was given on January 26, 1995, the partners of this project initiated work on October 1, 1994. As such, this progress report summarizes the work performed from project inception. The production and injection data, reservoir engineering data, and digitized and normalized log data were all completed sufficiently by the end of the quarter to start work on the basic reservoir engineering and geologic stochastic models. Basic reservoir engineering analysis began June 1 and will continue to March, 1996. Design work for the 5 observation/core holes, oil finger printing of the cored oil sands, and tracers surveys began in January, 1995. The wells will be drilled from July--August, 1995 and tracer injection work is projected to start in October, 1995. A preliminary deterministic 3-D geologic model was completed in June which is sufficient to start work on the stochastic 3-D geologic model. The four proposed horizontal wells (two injectors and two producers) have been designed, equipment has been ordered, and the wells will be drilled from mid-August through September. Four existing steam injection wells were converted to hot water injection in March, 1995. Initial rates were kept low to minimize operational problems. Injection rates will be increased significantly in July
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Feasibility of optimizing recovery and reserves from a mature and geological complex multiple turbidite offshore California reservoir through the drilling and completion of a trilateral horizontal well. Annual report, September 1, 1995--December 31, 1996
The main objective of this project is to devise an effective re-development strategy to combat producibility problems related to the Repetto turbidite sequences of the Carpinteria Field. The lack of adequate reservoir characterization, high-water cut production, and scaling problems have in the past contributed to the field`s low productivity. To improve productivity and enhance recoverable reserves, the following specific goals were proposed: develop an integrated database of all existing data from work done by the former ownership group; expand reservoir drainage and reduce sand problems through horizontal well drilling and completion; operate and validate reservoir`s conceptual model by incorporating new data from the proposed trilateral well; and transfer methodologies employed in geologic modeling and drilling multilateral wells to other operators with similar reservoirs. A computer based data retrieval system was developed to convert hard copy documents containing production, well completion and well log data into easily accessible on-line format. To ascertain the geological framework of the reservoir, a thorough geological modeling and subsurface mapping of the Carpinteria field was developed. The model is now used to examine the continuity of the sands, characteristics of the sub-zones, nature of water influx and transition intervals in individual major sands. The geological model was then supplemented with a reservoir engineering study of spatial distribution of voidage in individual layers using the production statistics and pressure surveys. Efforts are continuing in selection of optimal location for drilling and completion of probing wells to obtain new data about reservoir pressure, in-situ saturation and merits of drilling a series of horizontal wells
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A simulation-based reservoir management program
There are more than 5,200 independent oil and gas producers operating in the US today (based on current IPAA membership figures). These companies are playing an increasingly important role in production of hydrocarbons in California and elsewhere in the US. Pacific Operators Offshore, Inc., in a historic collaboration with its government royalty owners, the California State Lands Commission and the Minerals Management Service of the US Department of Interior, is attempting to redevelop the Carpinteria Offshore Field after two-and-a-half decades of production and partial abandonment by a previous operator. This paper will describe a project which focuses on the distribution of advanced reservoir management technologies (geological, petrophysical, and engineering) to independent producers like Pacific Operators Offshore, Inc. The evolving information highway, specifically the World Wide Web (WWW), serves as the distribution medium. The project to be described in this paper is an example of the implementation of a reservoir management tool which is supported by distributed databases, incorporates a shared computing environment, and integrates stochastic, geological, and engineering modeling