Pressure-Transient Analysis for Cold-Water Injection into a Reservoir Coupled with Wellbore-Transient-Temperature Effects

Presented here is an analytical framework to assess the impact of transient-temperature changes in the wellbore on the pressure-transient response of cold-water injection wells. We focus attention on both drawdown and falloff periods in a well after injection. Historically, these pressure data have been used to calculate reservoir properties concerning flood-efficiency and completion properties (formation permeability/thickness, mechanical skin, and fluid-bank mobilities). One key question addressed in this paper is whether the effects of thermal heating of wellbore fluids during a falloff survey can mask the pressure signature of a two-region composite reservoir. The pressure deflections required to detect mobility changes can be relatively small compared with pressure changes induced by temperature effects in the well. The framework proposed in this paper allows for the numerical evaluation of the contribution of each. Previously, researchers have studied multiple bank-transient-injection problems extensively for the case of reservoir flow and pressure drop, even for nonisothermal problems. The effect of temperature changes in the wellbore and overburden are seldom discussed, however. It is demonstrated in this paper that these effects can, in some cases, be substantial, and it is worthwhile to incorporate them into an interpretation model. The results of this paper are useful for planning and designing a pressure-falloff survey to minimize the adverse effect that heating of wellbore fluid by overburden rock can have on the pressure-transient signature. The theory can also be used to analyze existing data affected by the phenomenon. A real-field case study is shown for a cold-water injector where pressure-falloff data have been affected by temperature changes. The analytical model fits the field data closely when parameters are adjusted within reservoir-property-uncertainty ranges.