Conceptual Study of a Well-Fracture-Well Type Fluid Circulation System for EGS

Abstract

A new arrangement applicable to a single-well EGS is introduced. The new element of the concept is the application of a wing fracture or a series of wing fractures parallel with the centerline of an EGS well. During hydrofracturing, each wing fracture is hydraulically connected to the well over a section from which it is created. A straight well in an ideal arrangement lays in a planar wing fracture intersecting each other along the entire lateral extension of the fracture. A directionally drilled well may follow a planar fracture, intersecting it at multiple points around a section at which the fracture approximates the osculating plane of the well. In a completed EGS, separation of the incoming and returning fluid flows is accomplished by the liner of the well; and a grouted area within the fracture close to the well. The injected grout as an island forces the return flow toward the edge area of the fracture. The sealing grout also acts as a permanent support to prop the fracture open without the need for opening it by hydraulic pressure. In a single-well, direct flow arrangement, the coolant fluid passes from the injection point along a series of well-fracture-well segments to the production point during operation. In a single-well, counter-current flow arrangement, the coolant fluid is injected through a separated pipe in the well in one direction into the farthest point in the fracture; the fluid is then flows back along the fracture plane in the opposite direction until it returns through the well, creating a geologic heat exchanger over a large fracture surface. Examples of the new arrangement are presented with single, and multiple wing fractures along a single EGS well. Numerical simulation results are shown from the hydraulic and thermal models of the new EGS layout. Conclusions are drawn regarding the efficiency of the new flow system with a grouted island close to the center of the planar fracture in comparison with a single input, single output, unblocked EGS fracture.