Cyclic Pressure Pulsing: A Promising Method to Improve Recovery from Hydraulically-Fractured Stripper Wells of Appalachian Basin

Abstract

Cyclic-pressure pulsing is a single-well EOR method that has been successfully applied in naturally fractured systems. The process is driven through diffusion of the injected gas from the fractures into the matrix. After diffusing, the gas displaces remaining oil towards the fractures, which eventually results in higher production rates. In this study, the process is studied for hydraulically fractured wells to understand its effectiveness. Injected gas composition is varied as pure nitrogen, pure carbon-dioxide and mixture of these gases. Appalachian Basin is considered as a case study, due to many hydraulically-fractured, stripper wells in the region. A numerical compositional simulation model is constructed and flow around the hydraulic fracture is represented using local grid refinement. A 36 API gravity crude oil taken from Appalachian Basin is defined, and reservoir characteristics represent the Appalachian Basin sandstones. The process is analyzed with a large number of simulation runs from the perspectives of operational, reservoir, and hydraulic-fracture characteristics. Key sensitivity parameters for the operational part are chosen as the injection rate, injection/soaking durations, and the economic rate limit to stop the production and restart the injection. For the reservoir/hydraulic fracturing part, reservoir permeability, hydraulic fracture's effective permeability, thickness and half-length are chosen. After collecting key performance indicators, a proxy model was constructed to obtain a screening tool for future studies and to understand key sensitivities. The study showed that within the ranges studied, cyclic-pressure pulsing with both carbon-dioxide and nitrogen can be successfully applied for 3 to 12 cycles within a 20-year project period with discounted injection efficiencies representing net present values greater than zero for any realistic oil price scenario. To ensure maximum efficiency, injection and hydraulic fracture related design parameters must be considered. Injection volume and overall effectiveness of the hydraulic-fracture (width, half-length, permeability) affect the performance significantly. While benefits of soaking are clearly observed, the duration does not significantly affect the process. Economic limit must be optimized for balancing the remaining energy in the reservoir before starting the injection and maximizing barrels of oil recovered as early as possible.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016