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This study deals with the determination of the region within a geothermal reservoir that best provides the volumetric average reservoir pressure. This is performed in order to able to determine the proper location for an observation well through which the volumetric average reservoir pressure could be recorded. In this study a numerical work is carried out for determining the proper location for an observation well to be placed for various configurations of reservoir outer boundary conditions and well configurations. Even though either a single well or two wells are used, the results may be generalized to cases where there are multiple wells in the reservoir by using the production/injection well locations as the region where production/injection occurs. The locations of the wells and boundary conditions have been chosen as to cover many of the possible configurations that could take place in practice. The boundary conditions used in this study are of two types; a sealed outer boundary and a constant pressure outer boundary for mimicking the effects of a recharge source. Wells are considered to be either producer or injector wells where a constant rate production or injection scheme is applied. The effects of faults are also considered in this study where the faults are modeled as a very high permeability medium. The results of this study provide various maps for various boundary and well configurations from which the engineer may be able to determine qualitatively where to place the observation well. This study is original in the sense that to the authors knowledge no such study exists in the literature. This study will be filling the gap.

This work focuses on transient temperature responses of single-phase liquid-water geothermal reservoirs to constant-rate drawdown and buildup tests. New analytical and approximate solutions are presented for predicting drawdown and buildup sand-face transient temperature behaviors of a fully penetrating vertical well in an infinite-acting homogeneous reservoirs. The solutions account for the effects of Joule-Thomson (J-T) heating/cooling, transient adiabatic fluid expansion/compression, convection, and conduction. The solutions are compared and verified with the solutions from three different non-isothermal simulators that solve the mass and thermal energy balance equations rigorously and simultaneously. The impacts of various parameters such as wellbore storage, skin zone near the wellbore, thermal conductivity, and outer reservoir boundary conditions on the sand-face temperature responses are also investigated and discussed. Drawdown and buildup sand-face temperature data are shown to exhibit three infinite-acting radial flow (IARF) periods (represented by semi-log straight-line equations); early-time IARF reflecting the adiabatic expansion/compression effects in the skin zone if it exists, intermediate-time IARF reflecting the J-T effect in the skin zone, and late-time IARF reflecting the J-T effect in the non-skin zone. In an accompanying paper (Part II), we present an interpretation and analysis methodology based on the analytical solutions derived here for parameter estimation from temperature transient data jointly with pressure transient data. (C) 2016 Elsevier B.V. All rights reserved.