Case Study of a Gulf Coast Layered Reservoir Using Multirate Transient Testing

Abstract

ABSTRACT This paper presents the results of the first application of multilayer, multirate transient pressure testing techniques to the evaluation of a well located in an offshore area of North America. The primary purpose of the case study was to understand the depletion mechanisms of individual layers within the multilayer reservoir. The evaluation was performed using multirate transient pressure analysis and production logging techniques. The study, performed in a well with a three-layered reservoir completion, illustrates the potential for understanding many of the production and reservoir system problems found in complex geologic environments like the Gulf Coast. The reservoir parameters (permeability, skin factor and pressure) were estimated for each of the layers and the results were compared to those from conventional analyses. The results indicate that the depletion mechanisms of the separate layers are different and that production may be lost because of aquifer water influx from one layer. The understanding of the real reservoir behavior allows workover procedures to yield the optimum hydrocarbon recovery. Multilayer well test techniques were used, i.e., sequential flow tests with continuous downhole flow rate and pressure measurements at the top of each layer obtained using production logging tools. The analysis techniques utilized for the multilayer reservoir evaluation include convolution, deconvolution, pressure derivative and rate normalization. The interpretation was substantiated using a nonlinear regression to fit the measured downhole flow rate or pressure data with a layered reservoir model. This case study shows that these advanced reservoir evaluation techniques can have widespread applicability in offshore wells. The multilayer testing technique can be used as a monitoring device to develop pressure depletion profiles of different layers and optimize the recovery of reserves.