Advanced Reservoir Characterization and Evaluation of C02 Gravity Drainage in the Naturally Fractured Sprayberry Trend Area

Abstract

The overall goal of this project is to assess the economic feasibility of CO 2 flooding the naturally fractured Spraberry Trend Area in west Texas. This objective is being accomplished by conducting research in four areas: 1) extensive characterization of the reservoirs, 2) experimental studies of crude oil/brine/rock (COBR) interaction in the reservoirs, 3) analytical and numerical simulation of Spraberry reservoirs, and, 4) experimental investigations on CO 2 gravity drainage in Spraberry whole cores. This report provides results of the first quarter of 1998 in the third area.The CO 2 flooding project is going into Phase II, i.e., Field Demonstration. Pilot scale reservoir simulation for the CO 2 flooding is necessary for both initial pilot design and design modification in the future. In order to perform a quality simulation study with a dual porosity reservoir simulator, it is vitally important to use reliable reservoir parameters as input data. In the first quarter of 1998, we conducted investigations on refinement of reservoir parameters to be used in the pilot scale simulation of CO 2 flooding the naturally fractured Spraberry Trend Area reservoir. We concluded that the absolute permeability of the rock matrix to be input into the dual porosity simulator should be the permeability determined from drainage oil-water capillary pressure curve rather than air permeability, water permeability, or oil permeability. The secondary porosity and the on-trend fracture permeability have been estimated using a simple mathematical model based on fracture characterization data. The results are consistent with that derived from well test analyses and are being verified using coreflood data and a newly developed scaling model presented in this document.iv