Heat Transfer Applications for the Stimulated Reservoir Volume

摘要

Multistage hydraulic fracturing of horizontal wells enables creation of a Stimulated Reservoir Volume (SRV). An idealization of the SRV for shale gas production is a rectangle of length equal to horizontal well length and width equal to twice the half length of the created hydraulic fractures. This paper discusses the use of an analogous SRV design for two novel thermal 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. The water is heated by contact with the hot rock, and 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. Technical and economic feasibility of applying this technique to Haynesville Shale are evaluated. The second application considers using a similarly created SRV for producing oil from oil shale. Thermal decomposition of kerogen to oil and gas requires heating the oil shale to 700oF. We propose to inject high quality saturated steam generated using a small scale nuclear plant for heating the formation to the necessary temperature. Using the same flow geometry as in the previous case, produced water would be reheated and reinjected in a closed cycle. The energy required for steam heating is compared to other approaches in the literature. Analytical and numerical models are developed to evaluate the number, dimensions, and spacing of fractures sufficient to achieve heat transfer in a reasonable length of time for each of these applications.