Methane Production From Geopressured Aquifers
Authors: Doherty M.G. , Randolph P.L. , Rogers L.A. , Poonawala N.A. 
Published: December 2007

Summary
Several assessments of geopressured aquifers have been performed during the past several years. This paper reexamines an earlier SPE publication in light of data available from recent research and geopressured aquifer well tests. What has been learned about geopressured aquifers in terms of reservoir parameters is incorporated to narrow the ranges of uncertainty in conducting parametric studies to predict production of natural gas. Economic sensitivity of the reservoir parameters is studied in terms of a reassessment of the capital investment and operating costs in constant (1980) dollars required for a complete geopressured aquifer production system. Test data from the U.S. DOE geopressured/geothermal well, Pleasant Bayou Well 2, are used in the analysis.

Introduction
A few years ago, Randolph examined the potential for natural gas production from U.S. gulf coast geopressured aquifers. Since that time, a number of encouraging as well as discouraging findings have narrowed the ranges of uncertainty for some parameters. In other cases, more questions have been raised as a result of the information compiled. An interesting metamorphosis has taken place concerning emphasis of the public domain program under the sponsorship of the U.S. DOE. Early in the program history, brine production from geopressured aquifers was considered primarily for electricity generation through the hydraulic and thermal energy produced. This sentiment gradually changed to an emphasis on the production of the methane dissolved in the brine. Now another change is occurring, With the realization that one important cost factor of the produced methane involves brine disposal, utilization of the hydraulic and thermal potential to help reduce reinjection costs is being reconsidered. In addition, using the pressure and the heat produced to reinject fluids into the original aquifer for higher recovery of brine and methane through pressure maintenance is under consideration. However, the current thrust is aimed at gas production while examining ways to reduce expenses and/or increase revenues. A positive regulatory action deregulated geopressured aquifers along with some other unconventional gas sources. But the question is: "Can the market bear a price sufficiently high to encourage development of geopressured aquifers in general? "In the past, interviews with individuals experienced in natural gas exploration in geopressured areas revealed a pessimistic view on methane production from geopressured aquifers. Recent interactions indicate a slight moderation of this earlier appraisal--interest, or perhaps curiosity, on the part of the private sector seems to be increasing, judging from attendance at periodical U.S. DOE/industry geopressured-geothermal forum meetings--but negative and cautious opinions prevail.

Computational Procedures
When examining the cost significance of various parameters, computational procedures need to be defined carefully. An extension of the reservoir engineering techniques published by Bernard for a bounded circular aquifer as discussed in Ref. 1 and modified for use in IGT's one-dimensional, single-phase reservoir simulator are used. Economic assessments are based on a standard discounted cash flow (DCF) analysis with constant 1980 dollars to eliminate the effect of inflation. The Appendix provides details on the computational procedures.

Base Case
A substantial amount of work resulted in characterizing the geopressured and geothermal resource and defining reservoir parameters in Louisiana and Texas. Reviews of the geopressured aquifer resource and data from geopressured/geothermal test wells have been published. Already, some interpretations of these data are leading to differing conclusions. Extensive studies also have been conducted on the environmental and socioeconomic aspects of geopressured/geothermal development around the gulf coast area.
JPT
P. 1591^