Pressure Transient Analysis for Cold Water Injection into a Reservoir with a Coupled Analytic Wellbore Model

Abstract

In this short technical note we lay out an analytical framework to assess the impact of transient temperature changes in the wellbore on pressure transient response of cold water injection wells. We focus attention on the falloff period of an injector following injection. Historically, these pressure data have been used to calculate reservoir properties concerning flood efficiency and completion properties, e.g.: 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-zone composite reservoir. The pressure deflections required to detect mobility changes may be relatively small compared to 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 non-isothermal 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 minimise the adverse effect that heating of wellbore fluid by overburden rock may have on the pressure transient signature. The theory can also be used to analyse existing data affected by the phenomenon.