Extending Shale Gas Well Life with Low Grade Geothermal Power - Haynesville Case

摘要

The hydraulic fracture network of a shale gas well, after its production rate has dropped below the economic limit, can be used for low grade geothermal heat extraction. Conceptually, the Stimulated Reservoir Volume (SRV) for the shale gas well consists of multiple parallel transverse fractures created along one horizontal well. The idea investigated is to connect the created hydraulic fractures with horizontal wells. For a single well SRV, horizontal wells could be drilled at the fracture tips. However, for multiple SRVs, if the tips of fractures created from adjacent parallel horizontal wells are sufficiently connected, it may be possible to use existing horizontal wells. Cold water is to be pumped into one horizontal well connected to the network of parallel fractures. The water is heated by contact with the hot rock, and then recovered through a second horizontal well connected to the same network of parallel fractures and parallel to the first horizontal well. The basis of this concept is to use the already created SRV for heat transfer purposes. Considering the low thermal conductivity of shale, we show simulations indicating that typical well completions in the Haynesville Shale provide sufficient heat transfer area to heat injected water to temperatures suitable for electric power generation. After flowing through the SRV fracture network, produced hot water is passed through a heat exchanger, transferring heat to a working fluid in the power plant. The vaporizing working fluid is expanded across a turbine to drive a generator and produce electricity. The hot water, upon exiting the heat exchanger, is injected back into the reservoir to collect additional heat, thus forming a closed loop cycle.