Improving the Connectivity Between Injection and Production Wells in Enhanced Geothermal Systems Using Fiber Optic Data

Abstract Enhanced geothermal systems must have excellent connectivity between injection and production wells to effectively circulate and heat fluids for efficient energy recovery. This study demonstrates the use of fiber optic data to improve injection-production well connectivity in the field. We cemented a high temperature optical fiber bundle in the production well at the Forge enhanced geothermal site. Stimulation treatments from the injection well (16A) were monitored at the production well (16B) and DTS and Rayleigh Frequency Shift Distributed Strain Sensing data were collected. This data was analyzed to determine the locations of the Fracture Driven Interactions ("frac hits") at the cased (but sealed) production well (16B). The location and design of perforation clusters in the production well were specified based on this analysis. Perforating and fracturing the production well using this strategy resulted in fractures that connected well with the fractures from the injection well as tested by a post hydraulic fracturing, cross well circulation tests. Strain change and strain change rate data is presented, clearly showing the location of fractures propagating from the injection well to the production well. The fracture geometry was expected to be potentially complex due to natural fractures and fracture turning caused by stress shadow effects. The fiber optic strain data allowed us to identify, in real time, the most likely location of these fractures in the vicinity of the production well. This in turn allowed us to select not only locations of perforation clusters in the production well, but also adjustment of individual cluster spacing that would initiate fractures most likely to intersect the injection well fractures. These engineered completion designs (used in the production well) differ substantially (in perforation location and design) from the geometric completions used in the injection well. Fluid circulation tests run after both wells were stimulated confirmed good inter-well connectivity. This level of success could not have been achieved without the use of the fiber optic strain data used to design the completions in the production well. We have developed and demonstrated in the field a reliable method to ensure good connectivity between fractures initiated at injection and production wells in enhanced geothermal systems. This connectivity is essential to the success of EGS, and these results demonstrate a breakthrough in EGS design processes and procedures.