Heat Transfer Applications for the Stimulated Reservoir Volume
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Multistage hydraulic fracturing of horizontal wells continues to be a major technological tool in the oil and gas industry. Creation of multiple transverse fractures in shale gas has enabled production from very low permeability. The strategy entails the development of a Stimulated Reservoir Volume (SRV), defined as the volume of reservoir, which is effectively stimulated to increase the well performance. An ideal model for a shale gas SRV is a rectangle of length equal to horizontal well length and width equal to twice the half length of the created hydraulic fractures. This project focused on using the Multistage Transverse Fractured Horizontal Wells (MTFHW) for two novel applications. The first application considers using the SRV of a shale gas well, after the gas production rate drops below the economic limit, for low grade geothermal heat extraction. Cold water is pumped into the fracture network through one horizontal well drilled at the fracture tips. Heat is transferred to the water through the fracture surface. The hot water is then recovered through a second horizontal well drilled at the other end of the fracture network. The basis of this concept is to use the already created stimulated reservoir volume for heat transfer purposes. This technique was applied to the SRV of Haynesville Shale and the results were discussed in light of the economics of the project. For the second application, we considered the use of a similarly created SRV for producing hydrocarbon products from oil shale. Thermal decomposition of kerogen to oil and gas requires heating the oil shale to 700 degrees F. High quality saturated steam generated using a small scale nuclear plant was used for heating the formation to the necessary temperature. Analytical and numerical models are developed for modeling heat transfer in a single fracture unit of MTFHW. These models suggest that successful reuse of Haynesville Shale gas production wells for low grade geothermal heat extraction and the project appears feasible both technically and economically. The economics of the project is greatly aided by eliminating well drilling and completion costs. The models also demonstrate the success of using MTFHW array for heating oil shale using SMR technology.