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Thermal Expansion Behavior of Cerro Prieto Sandstones and Other Sedimentary Rocks Under Stress

Description: This paper describes the experimental work and presents the results of a research program carried out to investigate the thermal expansion behavior of sedimentary rocks under high stress conditions. The aspects that were investigated include the effects of temperature, temperature cycling, and confining pressure. Furthermore, the validity of the usual assumption on thermal expansion isotropy was investigated. On the other hand, the matrix thermal expansion concept is analyzed and its physical meaning and aplications are discussed. The effect of temperature on porosity is also a subject investigated regarding experimental methods for its estimation and comparison of earlier results. The experiments carried out consisted basically of thermal strain versus temperature measurements on jacketed and unjacketed samples subjected to different confining pressures and covering the temperature range from 25 C to 280 C and the pressure range from 3.0 MPa to 34.4 MPa. A review of earlier work is included as a reference frame to discuss and compare the results of this work, as well as to emphasize the limited extent of the research on thermal expansion behavior of sedimentary rocks that had been accomplished. Results are presented by means of thermal strain versus temperature curves and tabular data of thermal expansion coefficients. Several important conclusions for laborarory and field applications are reached from each of the aspects investigated. The wide research scope of considerable amount of data reported may represent an important contribution to the knowledge of thermal expansion behavior of sedimentary rocks.
Date: December 15, 1983
Creator: Contreras, E. & Bermejo, F.
Partner: UNT Libraries Government Documents Department

A Method to Recover Useful Geothermal-Reservoir Parameters from Production Characteristic Curves (1) Steam Reservoirs

Description: In this paper we develop and demonstrate a method to estimate the reservoir pressure and a productivity index for vertical steam wells, from its production characteristic (also called output) curves. In addition, the method allows to estimate the radius of influence of the well, provided that a value of the reservoir transmisivity is available. The basic structure of the present method is: first, the measured well head mass flowrates and pressures are transformed to downhole conditions by means of a numerical simulator; then, the computed downhole variables are fitted to a simple radial model that predicts the sandface flowrate in terms of the flowing pressure. For demonstration, the method was applied to several steam wells from the Los Azufres Geothermal field. We found excellent agreement of the model with this ample set of field data. As a bonus, the processed data allowed several inferences about the steam producing zone of the reservoir: that the wells considered produce from relatively isolated pockets of steam, which are probably fed by near-by inmobile water; and that these feed zones are in poor hydraulic communication with the field surface waters. our method are that it provides a way to retrieve important reservoir information from usually available production characteristic curves, and that the method works from easily and accurately taken wellhead measurements.
Date: December 15, 1983
Creator: Iglesias, E.; Arellano, V.; Garfias, A.; Miranda, C.; Hernandez, J. & Gonzalez, J.
Partner: UNT Libraries Government Documents Department

A Method to Recover Useful Geothermal-Reservoir Parameters from Production Characteristic Curves (2) Hot Water Reservoirs

Description: In this paper we develop and demonstrate a method to estimate the reservoir pressure, a mass productivity index, and a thermal power productivity index for vertical water-fed geothermal wells, from its production characteristic (also called output) curves. In addition, the method allows to estimate the radius of influence of the well, provided that a value of the reservoir transmisivity is available. The basic structure of the present method is: first, the measured wellhead mass flowrate; and pressures are transformed to downhole conditions by means of a numerical simulator; then, the computed downhole variables are fitted to a simple radial model that predicts the sandface flowrate in terms of the flowing pressure. For demonstration, the method was applied to several wells from the Cerro Prieto geothermal field. We found very good agreement of the model with this ample set of field data. The main advantages of our method are that it provides a way to retrieve important reservoir information from usually available production characteristic curves, that it works from easily and accurately taken wellhead measurements, and that its results address the two main aspects of geothermal resource utilization, namely, mass and heat production.
Date: December 15, 1983
Creator: Iglesias, E.; Arellano, V. & Molinar, R.
Partner: UNT Libraries Government Documents Department

Chemical and Isotopic Evidence of Steam Upflow and Partial Condensation in Los Azufres Reservoir

Description: Data of chemical and isotopic composition of fluids from Los Azufres wells, collected over a two year period, provide evidence of a process of upward flow and partial condensation of steam in the reservoir, which explains part of the previously reported heterogeneity in isotopic composition of the liquid phase (Nieva et al, 1983). For the southern part of the field, a direct correlation is found between chloride and oxygen-18 concentrations, and an inverse correlation between these parameters and deuterium and carbon dioxide concentrations in the liquid phase of the reservoir. Chloride ion concentrations increase gradually from ca 660 ppm in the production zones of shallow wells to ca 1900 ppm in the case of deep wells. This observation agrees with predictions based on the well-known model for vapor dominated systems of White et al (1971). For the northern part of the field the same correlations are observed, except for the deuterium concentration which in this case correlates directly with oxygen-18. It is concluded that the same process of steam upflow occurs in the northern section but that some other process — perhaps a mixture with other hydrothermal fluid — is also occurring. 3 tabs., 16 refs., 8 figs.
Date: January 20, 1987
Creator: Nieva, D.; Verma, M.; Santoyo, E.; Barragan, R.M.; Portugal, E.; Ortiz, J. et al.
Partner: UNT Libraries Government Documents Department