Results of Reservoir Modeling of the Operation and Production of a Recompleted Gas Well in a Geopressured/Geothermal Reservoir in the Wilcox Formation, Texas, for Electricity Generation
- Ariel Esposito (National Renewable Energy Laboratory) | Chad Augustine (National Renewable Energy Laboratory)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- December 2014
- Document Type
- Journal Paper
- 1,151 - 1,161
- 2014.Society of Petroleum Engineers
- 5.3.2 Multiphase Flow, 3 Production and Well Operations, 5.6.1 Open hole/cased hole log analysis, 4.6 Natural Gas, 7.1.10 Field Economic Analysis, 5.1.5 Geologic Modeling, 5.9.2 Geothermal Resources, 5.2.1 Phase Behavior and PVT Measurements, 7.1.9 Project Economic Analysis, 5.1.1 Exploration, Development, Structural Geology
- recompleted wells, geopressured geothermal energy, natural gas, reservoir modeling
- 4 in the last 30 days
- 175 since 2007
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Geopressured/geothermal reservoirs are found throughout the Texas and Louisiana Gulf Coast region, generally starting at depths below 8,000 ft, and are characterized by high-temperature/high-pressure, brine-saturated layers of interbedded shales and sandstones with correspondingly large quantities of dissolved natural gas. The temperature of the brine from these formations is high enough that it could be used to run organic Rankine cycle or binary power plants to generate electricity, whereas the dissolved natural gas in the brine could be simultaneously collected and used to generate additional electricity or sold as a byproduct. However, there is uncertainty about whether these reservoirs can maintain adequate production over the 30-plus-year lifetime of the power plant, and about what the natural-gas-production profiles would look like over this lifetime to supplement revenue from the geothermal-electricity production. This paper uses reservoir modeling to simulate the operation and production of a recompleted gas well in a geopressured/geothermal reservoir in the Wilcox formation, Texas, to assess the feasibility of the use of such reservoirs to produce a constant flow rate of high-temperature brine over a 30-year production lifetime for electricity generation. Reservoir modeling is a tool that can help predict fluid-flow rate and natural-gas production from complex reservoirs over a long-term time frame. Multiphase-flow reservoir modeling is used in this study to provide insight on the viability of recovering hot geothermal brine for electricity production over a time frame of 30 years by use of an existing natural-gas well. For this study, data from an abandoned gas well in the Wilcox formation in Texas, including a well log and fluid-chemistry data, are used to create a reservoir model with multiple layers of sandstone and shale with properties inferred from the well log and flow tests. The modeling also considers the impact of the well-operation limitations for the abandoned well after it is recompleted, such as a maximum frictional pressure drop in the well, on the geothermal-brine- and methane-production profiles. To assess the impact of key reservoir characteristics such as reservoir volume and gas saturation on the flow rate of geothermal brine and natural gas over the long term, a parametric-sensitivity analysis is completed by use of a range of reasonable values for these key reservoir parameters. For all the reservoir volumes considered (1.42x107 to 5.90x107 acre-ft), the flow rate of both geothermal brine and natural gas is sustained over the 30-year production period and it is determined that reservoir longevity is not an issue for electricity production. The free-phase-gas saturation has an observable impact on flow, with a higher free-gas saturation leading to lower geothermal-brine- and methane-flow rates caused by gas choking the flow in the near-well region. Overall, the multiphase reservoir modeling results indicate that for the reservoir considered, the well can be operated so that production of hot geothermal brine can be maintained over the lifetime of a binary power plant close to the target flow rates and that the quantities of natural gas produced would be significant for the overall power-plant-project economics.
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