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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

Well test analysis for naturally-fractured reservoirs

Description: In this work pressure transient analysis for constant rate production and transient rate analysis for constant pressure production are presented for a naturally fractured reservoir. Constant producing pressure solutions, which define declining production rates with time, are presented. The solutions for the dimensionless flowrate and pressure are based on a model presented by Warren and Root (1963). The results obtained for a finite no-flow outer boundary are new and surprising. It was found that the flowrate shows a rapid decline initially, becomes nearly constant for a period, and then a final decline in rate takes place. A striking result of the present study is that ignoring the presence of a constant flowrate period in a type-curve match can lead to erroneous estimates of the dimensionless outer radius of a reservoir. A method to determine the permeability-thickness product for a naturally-fractured reservoir is presented. The method involves a semilog graph of the pressure difference log(anti p-p/sub ws/) vs shut-in time ..delta..t. The mathematical theory is based on the extended Muskat analysis for a homogeneous reservoir. A comparison is made with the Pollard method. It was found that both methods are mathematically related. The dimensionless matrix pressure and fracture pressure distributions are presented for both the constant rate case and constant pressure production. Interference tests for the constant rate production can be interpreted at long times using the line-source solution. For the constant pressure production case, the pressure array from the wellbore does not correlate with the line source solution.
Date: January 1, 1982
Creator: Da Prat, G. C.
Partner: UNT Libraries Government Documents Department