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Depletion modeling of liquid dominated geothermal reservoirs

Description: Depletion models for liquid-dominated geothermal reservoirs are derived and presented. The depletion models are divided into two categories: confined and unconfined. For both cases depletion models with no recharge (or influx), and depletion models including recharge, are used to match field data from the Svartsengi high temperature geothermal field in Iceland. The influx models included with the mass and energy balances are adopted from the petroleum engineering literature. The match to production data from Svartsengi is improved when influx was included. The Schilthuis steady-state influx gives a satisfactory match. The finite aquifer method of Fetkovitch, and the unsteady state method of Hurst gave reasonable answers, but not as good. The best match is obtained using Hurst simplified solution when lambda = 1.3 x 10{sup -4} m{sup -1}. From the match the cross-sectional area of the aquifer was calculated as 3.6 km{sup 2}. The drawdown was predicted using the Hurst simplified method, and compared with predicted drawdown from a boiling model and an empirical log-log model. A large difference between the models was obtained. The predicted drawdown using the Hurst simplified method falls between the other two. Injection has been considered by defining the net rate as being the production rate minus the injection rate. No thermal of transient effects were taken into account. Prediction using three different net rates shows that the pressure can be maintained using the Hurst simplified method if there is significant fluid reinjection. 32 refs., 44 figs., 2 tabs.
Date: June 1, 1984
Creator: Olsen, G.
Partner: UNT Libraries Government Documents Department

Decline curve analysis of production data from The Geysers geothermal field

Description: Production data for over two hundred wells at The Geysers geothermal field were compiled and analyzed. Decline curves for groups of wells with 5, 10, and 40 acre spacing are presented and compared to curves published previously by Budd (1972) and Dykstra (1981). Decline curves for several individual wells and leases are discussed to illustrate the effects of well spacing and location, as well as the heterogeneous nature of the reservoir.
Date: January 1, 1987
Creator: Ripperda, M. & Bodvarsson, G.S.
Partner: UNT Libraries Government Documents Department

Geothermal-well design handbook

Description: A simplified process is presented for estimating the performance of geothermal wells which are produced by natural, flashing flows. The well diameter and depth, and reservoir conditions must be known; then it is possible to determine the total pressure drop in a flowing well, and therefore to find the fluid pressure, temperature, and steam quality at the wellhead. By applying the handbook process to several input data sets, the user can compile sufficient information to determine the interdependence of input and output parameters. (MHR)
Date: February 1, 1982
Partner: UNT Libraries Government Documents Department

Computer simulation of production from geothermal-geopressured aquifers. Final report, October 1, 1978-January 31, 1983

Description: This is the final report on research conducted to improve the technical and scientific understanding of geopressured and geothermal resources. The effort utilized a computer to interpret the results of well tests and compile data on gas solubility in brine and the viscosity of brine. A detailed computer reservoir study of a geopressured test well that had been abandoned as a dry hole but became a commercial producer of hydrocarbons is presented. A number of special topical reports pertaining to test activities performed on Department of Energy test wells (MG-T/DOE Amoco Fee No. 1 Well, Leroy Sweezy No. 1 Well, and Pleasant Bayou No. 2 Well) are appended to the report. A referenced article written under this study that appeared in the Journal of Petroleum Technology is also reproduced.
Date: July 1, 1983
Creator: Doherty, M.G. & Poonawala, N.A.
Partner: UNT Libraries Government Documents Department

Analysis of Sweet Lake geopressured-geothermal aquifer

Description: The Sweet Lake geopressured-geothermal aquifer, located southeast of Lake Charles, Louisiana, is an aquifer modeled by a two-dimensional geopressured-geothermal simulator. This aquifer is a sandstone within the Frio formation at depths between 15,000 to 15,640 ft with a net porous thickness of 250 ft, a calculated in-situ permeability (from drawdown data) of 17 md, an estimated porosity of 24 percent, a uniaxial compaction coefficient of 4.5 x 10/sup -7/ psi/sup -1/ and a solution gas-water ratio of 11 SCF/STB all at the initial reservoir pressure of 12,060 psi. These parameters are typically pressure sensitive in geopressured-geothermal aquifers and are critically important to aquifer performance. Several simulation experiments are conducted which investigate the effects of varying initial values for these parameters with the experimentally determined values as means. The simulations give both optimistic and pessimistic expectations for aquifer performance. The expected life of the geopressured-geothermal well is reported for each simulation.
Date: January 1, 1983
Creator: Andrade, M.; Rago, F.M.; Ohkuma, H.; Sepehrnoori, K.; Peters, E. & Dorfman, M.
Partner: UNT Libraries Government Documents Department

Two-phase flow in geothermal energy sources. Final technical report

Description: A geothermal well consisting of single and two-phase flow sections was modeled in order to explore the variables important to the process. For this purpose a computer program was developed in a versatile form in order to be able to incorporate a variety of two phase flow void fraction and friction correlations. A parametric study indicated that the most significant variables controlling the production rate are: hydrostatic pressure drop or void fraction in the two-phase mixture; and, heat transfer from the wellbore to the surrounding earth. Downhole instrumentation was developed and applied in two flowing wells to provide experimental data for the computer program. The wells (East Mesa 8-1, and a private well) behaved differently. Well 8-1 did not flash and numerous shakedown problems in the probe were encountered. The private well did flash and the instrumentation detected the onset of flashing. A Users Manual was developed and presented in a workshop held in conjunction with the Geothermal Resources Council.
Date: July 1, 1981
Creator: Available, Not
Partner: UNT Libraries Government Documents Department

Existence and flow behavior of gas at low saturation in geopressured formations. Final report

Description: The first geopressured brine well tested for the Department of Energy produced gas and brine at a ratio far above the solution ratio for the gas in that brine. One explanation advanced was that the geopressured formation contained gas at a low saturation, and that this gas flowed into the well during the test. This hypothesis is examined and found to be untenable based on evidence from well logs, flow tests and thermodynamics, and on currently accepted concepts for migration and accumulation of petroleum. The probable explanation for the observed high gas/water ratios is shown to be a thin, tight gas-bearing layer in the case of one sand and an updip gas cap in the case of the second and tested.
Date: April 1, 1979
Creator: Matthews, C.S.
Partner: UNT Libraries Government Documents Department

Linear boundary detection using pressure buildup tests

Description: Linear boundary detection has received considerable attention in the past. Although linear boundaries are frequently suspected and observed in well tests, conventional interpretation methods rely upon the development of two straight lines, which may not occur in practice. This report introduces two new semilog type curve matching methods for finding the distance to linear boundaries using buildup tests. Idealized curves are plotted from analytical solutions generated using the image well concept. These curves are then collapsed mathematically to a single type curve. By matching field data to the semilog type curve, the distance to a linear boundary may be estimated. The new methods have distinct advantages. The transition zone is the most important feature of the pressure response for type curve matching. Since development of the second straight line is not required, the range of interpretable tests is greatly extended. No estimates of reservoir characteristics are required to calculate the distance to the boundary because dimensionless parameters are used. 23 refs., 15 figs., 1 tab.
Date: June 1, 1984
Creator: Fox, G.
Partner: UNT Libraries Government Documents Department

Prediction of the entropy production and pressure losses in two-phase flow from the mixing length theory

Description: The case of vertical two-phase flow is examined under the light of the mixing-length theory which was succesfully applied to turbulent flows. The purpose of the analysis is to obtain the pressure distribution along the geothermal wells. The well is modeled as a vertical pipe carrying a fluid of variable density; the density distribution is described by two parameters. The conservation equations are written in boundary layer coordinates and the pressure losses are computed through the entropy production function. The two-phase friction factor is defined and calculated and through this the pressure distribution of the geothermal well is obtained. Finally a comparison is made of the results emanating from this model to other theoretical predictions and known experimental data.
Date: April 1, 1980
Creator: Maeder, P.F. & Michaelides, E.E.
Partner: UNT Libraries Government Documents Department

Pressure losses in fracture-dominated reservoirs: the wellbore constriction effect

Description: Improved energy production from many types of energy reservoirs such as hot dry rock geothermal as well as hydraulically fractured oil, gas, and other geothermal reservoirs requires a better understanding of the fluid mechanics in the vicinity of the fracture-wellbore intersection. Typically, the aperture (smallest dimension) of a hydraulic fracture is only of the order of 1 mm (0.04 in.) so that reasonable energy production rates from geothermal systems require fairly large flow velocities within the fractures, particularly so as the wellbore-fracture intersection is approached. The high velocities and accelerations result in non-Darcian, often turbulent, flow and increased pressure losses. These flow phenomena were investigated experimentally for the simple case where the fracture plane and the wellbore drilling axis are orthogonal and the implication of these experimental results are examined by investigating the pressure losses in a hot dry rock reservoir.
Date: January 1, 1980
Creator: Murphy, H.
Partner: UNT Libraries Government Documents Department

Analysis of well tests with variable discharge

Description: The development of a general technique of analyzing well tests with variable flow rates is reported. The variable flow is approximated by a series of sequential straight line segments of arbitrary length and slope. (MHR)
Date: December 1, 1976
Creator: Tsang, C.F.; McEdwards, D.G.; Narasimhan, T.N. & Witherspoon, P.A.
Partner: UNT Libraries Government Documents Department

Non-Darcy flow in geothermal reservoirs

Description: The effects of non-Darcy flow laws are investigated for two geothermal reservoir types: multiphase and Hot Dry Rock (HDR). Long-term thermal behavior is emphasized as short-term pressure transient behavior is addressed in the oil field literature. Comparisons of Darcy and non-Darcy flow laws are made.
Date: January 1, 1982
Creator: Zyvoloski, G.
Partner: UNT Libraries Government Documents Department

Design and development of a test facility to study two-phase steam/water flow in porous media

Description: The approach taken at Lawrence Berkeley Laboratory to obtain relative permeability curves and their dependence on fluid and matrix properties is summarized. Thermodynamic studies are carried out to develop the equations governing two-phase steam/water flow in porous media and to analyze the relationship between mass flow rate and flowing enthalpy. These relationships will be verified against experimental results and subsequently will be used to develop a field analysis technique to obtain in-situ relative permeability parameters. Currently our effort is concentrated on thermodynamic analysis and development of an experimental facility. Some of the findings of the theoretical work are presented and also the design and development effort for the experimental facility is described.
Date: December 1, 1983
Creator: Verma, A.K.; Pruess, K.; Bodvarsson, G.S.; Tsang, C.F. & Witherspoon, P.A.
Partner: UNT Libraries Government Documents Department

Geothermal field case studies that document the usefulness of models in predicting reservoir and well behavior

Description: The geothermal industry has shown significant interest in case histories that document field production histories and demonstrate the techniques which work best in the characterization and evaluation of geothermal systems. In response to this interest, LBL has devoted a significant art of its geothermal program to the compilation and analysis of data from US and foreign fields (e.g., East Mesa, The Geysers, Susanville, and Long Valley in California; Klamath Falls in Oregon; Valles Caldera, New Mexico; Cerro Prieto and Los Azufres in Mexico; Krafla and Nesjavellir in Iceland; Larderello in Italy; Olkaria in Kenya). In each of these case studies we have been able to test and validate in the field, or against field data, the methodology and instrumentation developed under the Reservoir Technology Task of the DOE Geothermal Program, and to add to the understanding of the characteristics and processes occurring in geothermal reservoirs. Case study results of the producing Cerro Prieto and Olkaria geothermal fields are discussed in this paper. These examples were chosen because they illustrate the value of conceptual and numerical models to predict changes in reservoir conditions, reservoir processes, and well performance that accompany field exploitation, as well as to reduce the costs associated with the development and exploitation of geothermal resources. 14 refs., 6 figs.
Date: March 1, 1989
Creator: Lippmann, M.J.
Partner: UNT Libraries Government Documents Department

Analytic study of geothermal reservoir pressure response to cold water reinjection

Description: Derivation of the governing equation, including temperature effects, is given where the permeability-viscosity ratio is assumed to be an arbitrary function of r{sup 2}t. This function is represented by a Fermi-Dirac function, whose parameters are determined based upon physical considerations. The solution for the pressure change is analytic except for the final step, where a numerical integration is called for. The results and implications of the calculations are discussed. Summary and concluding remarks are presented.
Date: November 1, 1978
Creator: Tsang, Y.W. & Tsang, C.F.
Partner: UNT Libraries Government Documents Department

The hydrogeologic-geochemical model of Cerro Prieto revisited

Description: As the exploitation of the Cerro Prieto, Mexico, geothermal field continues, there is increasing evidence that the hydrogeologic model developed by Halfman et al. (1984, 1986) presents the basic features controlling the movement of geothermal fluids in the system. At the present time the total installed capacity at Cerro Prieto is 620 MWe requiring the production of more than 10,500 tonnes/hr of a brine-steam mixture. This significant rate of fluid production has resulted in changes in reservoir thermodynamic conditions and in the chemistry of the produced fluids. After reviewing the hydrogeologic-geochemical model of Cerro Prieto, some of the changes observed in the field due to its exploitation are discussed and interpreted on the basis of the model. 21 refs., 11 figs., 1 tab.
Date: January 1, 1989
Creator: Lippmann, M.J.; Halfman, S.E.; Truesdell, A.H. & Manon M., A.
Partner: UNT Libraries Government Documents Department

Analysis of nonisothermal injection and falloff tests in layered reservoirs

Description: The effects of reservoir layering and gravity segregation on nonisothermal injection and falloff tests are investigated. Results show that layering does not affect injection or falloff data if all the layers are permeable and accept fluids from the wellbore. In such cases, the average permeability, skin factor, and distance to the thermal front can be calculated using the techniques developed for homogeneous reservoirs. Special considerations have to be taken for cases where several layers are impermeable or are permeable but do not accept fluids of the well face. In the first case (impermeable layers), knowledge of the total thickness of the permeable layers is required for the existing techniques to be applied successfully. In the second case, the existing techniques cannot be applied, but characteristic responses from injection and falloff test are seen; therefore, this case can be identified easily. 13 refs., 8 figs.
Date: March 1, 1985
Creator: Halfman, S.E. & Benson, S.M.
Partner: UNT Libraries Government Documents Department