Leveraging supercritical CO2 to rejuvenate hydraulically fractured wells in unconventional reservoirs
It is not uncommon that wells drilled in shale reservoirs experience a large Initial Production (IP), followed by a significant drop in productivity a few months after hydraulic fracturing, leading to a reduced Estimated Ultimate Recovery (EUR), with primary recovery factors rarely exceeding 15%. This drop in productivity constrains the economics of wells, and entails operators to drill and stimulate more wells to retain a production rate target. Recently, refracturing has emerged as a means to increase the productivity of these wells. Numerous well interventions are required to isolate and perforate new zones in addition to the increased costs associated with fracturing fluids and proppant requirements. This paper investigates the physics of using supercritical CO2 as a secondary recovery method to rejuvenate hydraulically fractured wells in shale reservoirs. Under highly in-situ compressive stresses, diagenesis (fluid release) reactions provoke instabilities within the shale generating high porosity channels parallel to the minimum horizontal compressive stress. These channeling localization instabilities exist in ductile formations and are periodically interspersed in the shale's matrix. Induced hydraulic fractures intersect these channels, invoking pressure drawdown and drives production from these high velocity pillars. These channels close with well depletion, causing a sharp productivity decline. This paper predicts the critical fluid pressure above which pressure should be maintained by CO 2 injection to prevent the channels from closing. A computational model was developed for a shale play in Saudi Arabia as a case study. As the in-situ compressional stresses are high and its geologic setting is applicable, the critical fluid pressure is calculated. This paper aims to further the understanding of using CO2 as a secondary recovery technique and helps pave the road for a more sustainable future by sequestering CO2 into the ground and enhancing the EUR of shale oil and gas reservoirs.
