An Integrated Approach to Interval Pressure Transient Test Analysis Using Analytical and Numerical Methods

Abstract

Abstract In this paper we demonstrate that reservoir parameters such as horizontal and vertical permeability's may be determined in-situ from the analysis of interval pressure transient tests, and the results verified via accurate analytical and numerical modeling and simulation coupled with gradient based history matching techniques. From evaluation of simulated and field cases, and results of numerical experiments, we propose an integrated workflow for analysing wireline formation tester interval pressure transient tests using analytical and numerical methods. This approach includes simulation model generation, reservoir simulation, interactive sensitivity analysis and an automated history matching procedure for optimisation. An objective function with appropriate weightings for different data items is defined interactively. Weighting may include prior knowledge or statistically determined error variance in input data, sensor resolution, data uncertainty and regression schemes for data sets with responses of disparate magnitude. The MDT (Modular Dynamics Formation Tester)* tool provides the capability to conduct fluid sampling, controlled local production, standard transient and vertical interference tests. Such interval tests usually comprise of a drawdown and buildup-typically the tool is stationed in the borehole and two packers are set to hydraulically isolate a section of the formation. Observation probes or multiple probes mounted above the packers provide the capability of vertical interference testing within the near-wellbore formation. The methodology of analysing MDT transient data is similar to conventional pressure transient tests. However, specialised mathematical models are used for matching pressure and flow rate measurements. Conventionally, analytical models have been used in analyzing these tests. While computation of analytical models are fast, they may be too simplistic or inadequate for many test configurations. On the other hand, numerical models are more realistic and flexible. However, their use is more complex. Therefore, in our interpretation methodology we profess an integrated approach. Although gradient based techniques have been used in reservoir simulation for history matching of pressure and production performance of reservoirs for some time, our work focuses on their application to MDT interval pressure transient tests in combination with numerical well testing methods.