Superposition well-test method for reservoir characterization and pressure management during CO2 injection

Abstract:

As a significant fraction of a carbon storage project’s budget is devoted to site characterization and monitoring, there has been an intense drive in recent years to both lower cost and improve the quality of data obtained. Two data streams that are cheap and always available are pressure and flow rate measurements from the injection well. Falloff testing, in which the well is shut-in for some period of time and the pressure decline curve measured, is often used to probe the storage zone and look for indications of hydraulic barriers, fracture-dominated flow, and other reservoir characteristics. These tests can be used to monitor many hydromechanical processes of interest, including hydraulic fracturing and fault reactivation. Unfortunately, the length of the shut-in period controls how far away from the injector information may be obtained. For operational reasons these tests are typically kept short and infrequent, limiting their usefulness. In this work, we present a new analysis method in which ongoing injection data is used to reconstruct an equivalent falloff test, without shutting in the well. The entire history of injection may therefore be used as a stand in for a very long test. The method relies upon a simple superposition principle to transform a multi-rate injection sequence into an equivalent single-rate process. We demonstrate the effectiveness of the method using injection data from the Snøhvit storage project. We also explore its utility in an active pressure management scenario. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.