SPE 35167 Integrated Geologic, Engineering, and Financial Assessment of Gas Displacement Recovery in Texas D.K. Beike and M.H. Holtz, SPE, Bureau of Economic Geology, The University of Texas at Austin Copyright 1996, Society of Petroleum Engineers, Inc.

Abstract

A total of 57 commercially viable gas-displacement projects in Texas are classified into seven depositional environments. We collected reservoir and petrophysical data and depth and oil gravity for each reservoir, which gave us a generalized case model for each depositional environment. We also collected and analyzed information about the design of these projects, concentrating on pattern, spacing, and production processes previously applied.

Cost calculations that are presented are in accordance with a previous cost study by Beike and Holtz. Finances were analyzed for the case model of each depositional system according to net present value and internal rate of return. We also used an economic sensitivity analysis to investigate the effect of oil price, well spacing, and incremental recovery.

The potential for reserve additions from CO2 flooding in Texas is substantial. An additional 1,730 reservoirs are candidates for gas-displacement recovery. This set of reservoirs contains 70 BSTB of original oil in place, 23 BSTB of mobile oil, and 37 BSTB of residual oil. Factoring in a conservative reserve-growth recovery of an additional 10 percent of original oil in place, we estimate that future GDR projects could produce 7 BSTB in Texas. Most of this reserve growth will continue to come from restricted- to open-platform carbonate reservoirs in West Texas. Introduction and Objective A large volume of oil remains in existing Texas reservoirs (Fig. 1). Cumulative production to date represents approximately 25 percent of the original oil in place (OOIP), whereas a full 33 percent of the OOIP is remaining mobile oil and 37 percent is residual oil. Capturing this significant residual oil resource will require detailed reservoir characterization and application of enhanced oil recovery methods.

Over the last 20 yr much information has been gained from individual enhanced oil recovery (EOR) projects, most of which involved gas-displacement recovery (GDR). Such information invites integrated geologic-engineering-financial analysis of the projects that were commercially successful. Because economic-viability influences can be determined by means of this analysis, estimation of up-front capital costs can be made more accurately. These estimates in turn will lead to a possibility of increasing production of oil in mature Texas reservoirs.

Our objective was threefold:

  1. We began by determining characteristics of reservoirs in which GDR had been successfully applied. All geologic, engineering, regulatory, and economic characteristics were included.

  2. We analyzed the effect of GDR as an EOR method by examining production characteristics, incremental production, and recovery efficiency.

  3. We used the historical information to model the economic viability of GDR, in order to delineate the resource potential and sensitivity of additional oil production to salient influences.

GDR projects characterized were those that were implemented beyond the pilot stage. components of the GDR ProductIon EnvIronment Essentially four components form the flamework of possible EOR production. The first is EOR process technology, the GDR of which is analyzed herein, and which in turn is determined by geological environment, petrophysical parameters, and costs. The second component is macroeconomic environment, which is influenced by existing industry strength, import rate, and world oil production. P. 227

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