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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

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

Sourcebook on the production of electricity from geothermal energy. Chapter 2 (draft). Resource characteristics: reservoirs, wellheads and delivery systems. Part 3. Analysis of the flow in the reservoir: well system. [Includes glossary]

Description: This report is a preliminary version of material assembled for insertion in the Sourcebook on the Production of Electricity from Geothermal Energy currently being composed under ERDA (now DOE). An attempt has been made to develop the theory of the geothermal well in an ordered stepwise manner beginning from the three basic continuities and introducing each new idea systematically. A formal textbook approach is used.
Date: June 1, 1978
Creator: Ryley, D.J.
Partner: UNT Libraries Government Documents Department

Is geothermal simulation a catastrophe

Description: All numerical simulators of geothermal reservoirs depend upon an accurate representation of the thermodynamics of steam-water systems. These relationships are required to render tractable the system of balance equations derived from the physics of flow through porous media. While it is generally recognized that the steam-water system (i.e., two phase) is not in thermodynamic equilibrium, equilibrium thermodynamics are employed in its description. An alternative view based on non-equilibrium thermodynamics is presented. The underpinnings of this approach are found in a branch of topology generally referred to as catastrophe theory.
Date: January 1, 1980
Creator: Nguyen, V.V. & Pinder, G.F.
Partner: UNT Libraries Government Documents Department

Transition from mixed to forced convection for opposing vertical flows in liquid-saturated porous media

Description: Mixed-convection phenomena can occur within liquid-dominated geothermal reservoirs due to interactions of injected flows, or ground-water flows, with the buoyancy-induced fluid motion. This problem was studied experimentally and numerically for the case of opposing flows about a vertical heat source in a liquid-saturated porous medium. The ratio of the Rayleigh number (Ra) to the Peclet number (Pe) was identified as the nondimensional parameter which characterizes the relative influence of buoyancy-driven to pressure-gradient-driven fluid motion. The transition from mixed to forced convection was numerically determined to be (Ra/Pe) approx. = -0.5, where the minus sign denotes superimposed downflow. Agreement between measured and predicted thermal-field results showed that the finite-element code of Gartling and Hickox (1982 a,b) can be used to model low-temperature (single-phase) geothermal reservoirs throughout the natural, mixed, and forced convection regimes. 9 refs., 6 figs.
Date: January 1, 1985
Creator: Reda, D.C.
Partner: UNT Libraries Government Documents Department

Low-temperature hydrothermal resource evaluation

Description: The objectives of testing low-temperature hydrothermal wells are to characterize well response to production (injection), determine resource characteristics and project reservoir longevity. Testing procedures and analysis techniques differ in some respects from proven procedures in the oil and gas and ground water fields. Some basic definitions and standard techniques necessary for the evaluation of a fluid resource in an intergranular permeable reservoir are presented. Problems particular to a non-ideal thermal resource are outlined and some analytical techniques are discussed.
Date: May 5, 1980
Creator: Goldman, D.
Partner: UNT Libraries Government Documents Department

Geothermal two-phase flow: a selective, annotated guide to the literature. Report No. GEOFLO/7

Description: This bibliography includes only those references considered useful for the solution of problems facing a geothermal plant designer. Historical developments and flow models are discussed. (MHR)
Date: June 1, 1980
Creator: Bilicki, Z.; DiPippo, R.; Michaelides, E.E.; Kestin, J. & Maeder, P.F.
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 break-through 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 study presents four computer programs which employ linear or quadratic programming to solve the allocation problem. In addition, a program is presented which solves the injector configuration problem by a combination of enumeration and quadratic programming. The use of the various programs is demonstrated with reference both to hypothetical data and an actual data set from the Wairakei Geothermal Field in New Zealand.
Date: May 1, 1987
Creator: Lovekin, J.
Partner: UNT Libraries Government Documents Department