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Effects of Water Injection into Fractured Geothermal Reservoirs: A Summary of Experience Worldwide

Description: Reinjection of water into fractured geothermal reservoirs holds potential both for improvement and degradation of total energy recovery. The replacement of reservoir fluid can mean support of placement of reservoir pressures and also more efficient thermal energy recovery, but at the same time the premature invasion of reinjected water back into production wells through high permeability fractures can reduce discharge enthalpy and hence deliverability and useful energy output. Increases in reservoir pressure and maintenance of field output have been observed in operating fields, but unfortunately so too have premature thermal breakthroughs. The design of reinjection schemes, therefore, requires careful investigation into the likely effects, using field experimentation. This paper summarizes field experience with reinjection around the world, with the intention of elucidating characteristics of possible problems. The results summarized in this paper fall into three categories of interest: permeability changes dye to injection (both increases and decreases); the path followed by injected water (as indicated by tracer tests); and the thermal and hydraulic influences of injection on the reinjection well itself and on surrounding producers. [DJE-2005]
Date: June 1, 1982
Creator: Horne, Roland N.
Partner: UNT Libraries Government Documents Department

A convolution Boundary Element method for unsteady state groundwater flow in homogeneous aquifers

Description: In this paper, Boundary Element (BEM) solutions were obtained for the transient flow of fluids through homogeneous, anisotropic porous media. The Green’s function method with Euler method of forward time differencing and Laplace transform method have been used by previous authors. Unlike these methods, this paper uses the fundamental solution to the differential equation and the convolution behavior of the resulting integrals to obtain an implicit and stable solution. This allows large time steps to be taken without significant loss in accuracy. Comparison with the Laplace transform method and Green’s function method with discrete time stepping, for two test cases, show that the method is very accurate. The computations however, become quite storage intensive owing to the dynamic increase in the number of stored matrices. It has been shown elsewhere that for certain problems with both Dirichlet and Neumann boundary conditions, asymptotic expression generated from exact solution is needed for starting the computational procedure. The present formulation alleviates this requirement. These solutions are developed for use in the analysis of pressure transients in complex reservoir problems.
Date: January 1, 1988
Creator: Kikani, Jitendra & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

The effects of adsorption on injection into geothermal reservoirs

Description: The effects of an adsorbing phase on the injection of liquid and eventual production of vapor from a low-porosity, vapor dominated geothermal reservoir was studied. The magnitude of delay caused by adsorption, diffusion partitioning, preferential partitioning, and permeability variation were compared. Results were then compared to measured tracer production data at the Geysers to determine the most likely delay mechanism for injected tracer at the Geysers. A one-dimensional numerical model describing vapor flow in a porous medium in the presence of a sorbing phase was used to investigate the delay of injected tracer caused solely by the sorbing phase. An analytical model was used to describe delay effects due to diffusion partitioning of tracer from the vapor phase into the liquid phase. Properties of steam and tracer used in Geysers tracer studies were compared to determine the effects of preferential partitioning. Finally, a streamline model of a tracer study was used to determine the magnitude of permeability delays possible using permeability values measured at the Geysers. It was concluded that adsorption alone has very little effect on the delay of injected tracer indicating that little recharge of the adsorbed mass occurs for a typical injection program at the Geysers. Diffusion partitioning was shown to have a larger effect on tracer delay than adsorption while preferential partition was shown to have no effect. Permeability variation was shown to have the largest effect on tracer delay. Tracer delay was shown to be approximated closely by known permeability variations even when adsorption and diffusion effects are ignored.
Date: January 20, 1994
Creator: Hornbrook, John W. & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

An experimental study of adsorption in vapor-dominated geothermal systems

Description: We report results of steam adsorption experiments conducted for rock samples from vapor-dominated geothermal reservoirs. We examine the effect of the temperature on the adsorption/desorption isotherms. We find that the temperature effect is only important on the desorption such that the hysteresis becomes more pronounced as the temperature increases. The scanning behavior within the steam sorption hysteresis loop is also studied to investigate the behavior during repressurization. Collection of sets of data on the sorption behavior of The Geysers geothermal field in California is presented.
Date: January 26, 1995
Creator: Satik, Cengiz & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

The effects of CO{sub 2} on steam adsorption

Description: Water adsorption in geothermal reservoir materials was investigated by transient flow technique using steam and COz gas. Theoretical and experimental results indicate that water adsorption exists in vapordominated type of reservoir, but experiments in the past have been limited to pure gases. The common presence of CO2, a non-condensible gas, in a geothermal reservoir necessitated a study of the effect of partial CO2 concentration on adsorption. Experimental laboratory work using a crushed Geysers rock sample at low pressure was carried out. Transient pressure exerted by steam pressure inside the sample was measured against time during a desorption process. It was found that the partial presence of CO2 did not significantly affect the adsorption of water.
Date: January 20, 1994
Creator: Palar, Steve & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Optimization of Injection Scheduling in Geothermal Fields

Description: This study discusses the application of algorithms developed in Operations Research to the optimization of brine reinjection in geothermal fields. The injection optimization problem is broken into two sub-problems: (1) choosing a configuration of injectors from an existing set of wells, and (2) allocating a total specified injection rate among chosen injectors. The allocation problem is solved first. The reservoir is idealized as a network of channels or arcs directly connecting each pair of wells in the field. Each arc in the network is considered to have some potential for thermal breakthrough. This potential is quantified by an arc-specific breakthrough index, b{sub ij}, based on user-specified parameters from tracer tests, field geometry, and operating considerations. The sum of b{sub ij}-values for all arcs is defined as the fieldwide breakthrough index, B. Injection is optimized by choosing injection wells and rates so as to minimize B subject to constraints on the number of injectors and the total amount of fluid to be produced and reinjected. The use of the various methods is demonstrated with reference both to hypothetical data and an actual data set from the Wairakei Geothermal Field in New Zealand.
Date: March 21, 1989
Creator: Lovekin, James & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Matrix Diffusion and its Effect on the Modeling of Tracer Returns from the Fractured Geothermal Reservoir at Wairakei, New Zealand

Description: Tracer tests performed at the geothermal reservoir at Wairakei, New Zealand have been analyzed, using a mathematical and physical model in which tracer flows through individual fractures with diffusion into the surrounding porous matrix. Model calculations matched well with the observed tracer return profiles. From the model, first tracer arrival times and the number of individual fractures (the principal conduits of fluid flow in the reservoir) joining the injector-producer wells can be determined. if the porosity, adsorption distribution coefficient, bulk density and effective diffusion coefficient are nown, fracture widths may be estimated. Hydrodynamic dispersion down the length of the fracture is a physical component not taken into account in this model. Future studies may be warranted in order to determine the necessity of including this factor. In addition to the tracer profile matching by the matrix diffusion model, comparisons with a simpler fracture flow model by Fossum and Horne (1982) were made. The inclusion of the matrix diffusion effects was seen to significantly improve the fit to the observed data.
Date: December 15, 1983
Creator: Jensen, Clair L. & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Optimizing Reinjection Strategy at Palinpinon, Philippines Based on Chloride Data

Description: One of the guidelines established for the safe and efficient management of the Palinpinon Geothermal Field is to adopt a production and well utilization strategy such that the rapid rate and magnitude of reinjection fluid returns leading to premature thermal breakthrough would be minimized. To help achieve this goal, sodium fluorescein and radioactive tracer tests have been conducted to determine the rate and extent of communication between the reinjection and producing sectors of the field. The first objective of this paper is to show how the results of these tests, together with information on field geometry and operating conditions were used in algorithms developed in Operations Research to allocate production and reinjection rates among the different Palinpinon wells. Due to operational and economic constraints, such tracer tests were very limited in number and scope. This prevents obtaining information on the explicit interaction between each reinjection well and the producing wells. Hence, the chloride value of the producing well, was tested to determine if use of this parameter would enable identifying fast reinjection paths among different production/reinjection well pairs. The second aim, therefore, of this paper is to show the different methods of using the chloride data of the producing wells and the injection flow rates of the reinjection wells to provide a ranking of the pair of wells and, thereby, optimize the reinjection strategy of the field.
Date: March 24, 1992
Creator: Urbino, Ma. Elena G. & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Experimental study of water adsorption on Geysers reservoir rocks

Description: Experimental isotherms of water vapor adsorption/desorption on three geothermal reservoir rock samples have been measured at temperatures of 80, 100, 120 and 140°C. Initial surface status of the sample was found to influence the amount of water adsorbed. At low relative pressures, adsorption is the dominant process of water retention onto the rock samples. Adsorption/desorption hysteresis was observed to exist over the whole pressure range at all temperatures. Similar observations were made for all three samples. The results of this study suggest that adsorption is important in storing water in geothermal reservoir rocks not only in itself, but also in inducing capillary condensation.
Date: January 28, 1993
Creator: Shang, Shubo; Horne, Roland N. & Ramey, Henry J., Jr.
Partner: UNT Libraries Government Documents Department

Results of well-testing in the Broadlands geothermal field, New Zealand

Description: Although not the first hot-water geothermal field under development, the Broadlands geothermal field has shown itself to be quite different in behavior to other hot-water fields. The field was discharged some five years between 1966 and 1971, and has provided a large source of data in its as yet undeveloped state. This paper presents some of the results inferred from well-testing and highlights (1) the complexity of the system, (2) the importance of wellbore storage effects and (3) the effects of reinjection.
Date: January 1, 1978
Creator: Horne, Roland N.; Grant, Malcolm A. & Gale, Robert O.
Partner: UNT Libraries Government Documents Department

Analysing Spinner Measurements from Well Tests Using Computerized Interpretation Techniques

Description: The development of reliable spinner tools may help avoid much of the ambiquity which often accompanies well tests in geothermal wells, due to interlayer flows through the well bore. However, the use of both pressure and flow rate changes requires new methods of well test interpretation. The Stanford Geothermal Program has been developing microcomputer-based techniques for the simultaneous analysis of pressure and flow rate measurements. There are two key steps in the procedure. Firstly, the non-linear regression is achieved by calculating the gradients of the response (with respect to the unknown reservoir parameters) in Laplace space, and inverting numerically. Secondly, the variable flow rate is represented in terms of a superposition of many step changes - this was found to work better than a spline fit to the data. One problem was encountered when attempting to analyze data in which the spinner "stalled", causing a jump to zero flow rate. The method shows great promise in that the degrees of freedom on the interpretation are greatly reduced, the well bore storage effect disappears, and inter-feed flows do not affect the results.
Date: December 15, 1983
Creator: Horne, Roland N.; Guillot, Alain & Rosa, Adalberta
Partner: UNT Libraries Government Documents Department

On the Interpretation of tracer experiments

Description: Recently, two new developments appeared in the literature on modelling flow and transport in heterogeneous systems. The first one is the use of two different concentration variables namely, the resident and flux concentrations, in tracer studies. The second one involves representing the heterogeneity by means of a frequency disribution function for immobile phase size. Based on these developments, this work involves a classification of the solutions of transport equation in heterogeneous systems. It also demonstrates interpretation of tracer experiments in such systems. Distinguishing between the resident and flux concentration variables prevents the inconsistencies between theoretical solutions and actual conditions of experiments and hence, allows correct interpretation of tracer return profiles. Representing heterogeneities by means of frequency distribution functions allows representing matrix blocks of various sizes likely to exist in a fractured reservoir.
Date: January 20, 1994
Creator: Kocabas, Ibrahim; Horne, Roland N. & Brigham, William E.
Partner: UNT Libraries Government Documents Department

Optimizing reinjection strategy at Palinpinon, Philippines based on chloride data

Description: One of the guidelines established for the safe and efficient management of the Palinpinon Geothermal Field is to adopt a production and well utilization strategy such that the rapid rate and magnitude of reinjection fluid returns leading to premature thermal breakthrough would be minimized. To help achieve this goal, sodium fluorescein and radioactive tracer tests have been conducted to determine the rate and extent of communication between the reinjection and producing sectors of the field. The first objective of this paper is to show how the results of these tests, together with information on field geometry and operating conditions were used in algorithms developed in Operations Research to allocate production and reinjection rates among the different Palinpinon wells. Due to operational and economic constraints, such tracer tests were very limited in number and scope. This prevents obtaining information on the explicit interaction between each reinjection well and the producing wells. Hence, the chloride value of the producing well, was tested to determine if use of this parameter would enable identifying fast reinjection paths among different production/reinjection well pairs. The second aim, therefore, of this paper is to show the different methods of using the chloride data of the producing wells and the injection flow rates of the reinjection wells to provide a ranking of the pair of wells and, thereby, optimize the reinjection strategy of the field.
Date: January 1, 1991
Creator: Urbino, Ma. Elena G. & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Study of desorption in a vapor dominated reservoir with fractal geometry

Description: This paper is an attempt to model well decline in a vapor dominated reservoir with fractal geometry. The fractal network of fractures is treated as a continuum with characteristic anomalous diffusion of pressure. A numerical solver is used to obtain the solution of the partial differential equation including adsorption in the fractal storage space. The decline of the reservoir is found to obey the empirical hyperbolic type relation when adsorption is not present. Desorption does not change the signature of the flow rate decline but shifts it on the time/flow rate axis. Only three out of six model parameters can be estimated from field data, due to the linear correlation between parameters. An application to real well data from The Geysers field is presented together with the estimated reservoir, fractal space and adsorption parameters. Desorption dominated flow is still a questionable approximation for flow in fractal objects.
Date: January 26, 1995
Creator: Tudor, Monica; Horne, Roland N. & Hewett, Thomas A.
Partner: UNT Libraries Government Documents Department

Measurement of surface area and water adsorption capacity of The Geysers rocks

Description: The measurement of the quantity of adsorbed water on geothermal reservoir rocks allows a more realistic estimation of reserves for vapor-dominated geothermal reservoirs. This study measured adsorptioddesorption isotherms of water vapor on rock samples from Calpine Co.'s well MLM-3, both core fragments and well cuttings from Coldwater Creek steamfield and a number of well cuttings from well Prati State 12, Northwest Geysers steam field. Surface areas of these rock samples were measured using nitrogen adsorption at 77K. The results of these measurements suggest that surface area is a crucial factor in determining the amount of water adsorption. Analysis of the water adsorption data indicates that adsorption is the dominant phenomena in the matrix of the reservoir rock at relative pressures below 0.8. Depending on the structure of the rock, capillary condensation contributes considerably to the total water retention at relative pressure between 0.8 and 1.0. However, there is no clear distinction between adsorption and capillary condensation and it is difficult in the experiments to determine when complete saturation occurs. A significant result of these experiments was the demonstration that well cuttings show adsorption characteristics very much like those obtained from core fragments. This should allow further adsorption measurements to be made more extensively and at lower cost.
Date: January 20, 1994
Creator: Shang, Shubo; Horne, Roland N. & Ramey, Henry J. Jr.
Partner: UNT Libraries Government Documents Department

Adsorption characteristics of rocks from vapor-dominated geothermal reservoir at the Geysers, CA

Description: This paper reports on a continuing experimental effort to characterize the adsorption behavior of rocks from The Geysers steam field in California. We show adsorption results obtained for 36 rock samples. All of the adsorption isotherms plotted on the same graph exhibit an envelope of isotherms. The minimum and the maximum values of the slope (or rate of adsorption) and of the magnitude within this envelope of isotherms belonged to the UOC-1 (felsite) and NCPA B-5 (serpentine) samples. The values of surface area and porosity, and pore size distribution for 19 of the samples indicated a very weak correlation with adsorption. An interpretation of the pore size distributions and the liquid saturation isotherms suggests that the change in the slope and the magnitude of the adsorption isotherms within the envelope is controlled primarily by the physical adsorption mechanism instead of capillary condensation. Grain-size and framework grain to matrix ratio are found to be insufficient to characterize this adsorption behavior. An accurate identification of the mineralogy of the samples will be essential to complete this analysis.
Date: January 24, 1996
Creator: Satik, Cengiz; Walters, Mark & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Session 4: Geothermal Reservoir Definition

Description: The study of geothermal reservoir behavior is presently in a state of change brought about by the discovery that reservoir heterogeneity--fractures in particular--is responsible for large scale effects during production. On the other hand, some parts of a reservoir, or some portions of its behavior. may be unaffected by fractures and behave, instead, as if the reservoir were a homogeneous porous medium. Drilling has for many years been guided by geologists prospecting for fractures (which have been recognized as the source of production), but until recently reservoir engineers have not studied the behavior of fractured systems under production. In the last three years research efforts, funded by the Department of Energy and others, have made significant progress in the study of fractures. The investigations into simulation of fracture flow, tracer analysis of fractured systems, and well test analysis of double porosity reservoirs are all advancing. However, presently we are at something of a conceptual impasse in defining a reservoir as fractured or porous. It seems likely that future directions will not continue to attempt to distinguish two separate reservoir types, but will focus instead on defining behavior types. That is, certain aspects of reservoir behavior may be considered to be generally of the porous medium type (for example, field wide decline), while others may be more frequently fracture type (for example, breakthrough of reinjected water). In short, our overall view of geothermal reservoir definition is becoming a little more complex, thereby better accommodating the complexities of the reservoirs themselves. Recent research results already enable us to understand some previously contradictory results, and recognition of the difficulties is encouraging for future progress in the correct direction.
Date: December 1, 1983
Creator: Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Session: Reservoir Technology

Description: This session at the Geothermal Energy Program Review X: Geothermal Energy and the Utility Market consisted of five papers: ''Reservoir Technology'' by Joel L. Renner; ''LBL Research on the Geysers: Conceptual Models, Simulation and Monitoring Studies'' by Gudmundur S. Bodvarsson; ''Geothermal Geophysical Research in Electrical Methods at UURI'' by Philip E. Wannamaker; ''Optimizing Reinjection Strategy at Palinpinon, Philippines Based on Chloride Data'' by Roland N. Horne; ''TETRAD Reservoir Simulation'' by G. Michael Shook
Date: January 1, 1992
Creator: Renner, Joel L.; Bodvarsson, Gudmundur S.; Wannamaker, Philip E.; Horne, Roland N. & Shook, G. Michael
Partner: UNT Libraries Government Documents Department