Evaluation of EOR Potential by Gas and Water Flooding in Shale Oil Reservoirs

The demand for oil and natural gas will continue to increase for the foreseeable future; unconventional resources such as tight oil, shale gas, shale oil will pose an irreplaceable role in oil and gas industry to fill the gap between demand and supply. With the relatively modest natural gas price, producing oil from unconventional shale reservoirs, which are less common and less well understood than conventional sandstone and carbonate reservoirs, has attracted more and more interest from oil operators. Through many tremendous efforts on the development of shale resources, the horizontal well-drilling with multiple transverse fractures has proven to be an effective method for shale gas reservoirs exploitation and it has also been used in extracting oil from shale reservoirs by some operators. However, the oil recovery is very low (5-10%). For the important role of shale resources in future oil and gas industry, more stimulation and production strategies must be considered and tested to find better methods to improve oil production from shale reservoirs. Gas flooding and water flooding, relatively simple and cheaper EOR techniques, which have been successfully implemented in conventional and some unconventional tight oil reservoirs for a long time, are considered in our work. A black-oil simulator developed by Computer Modeling Group Ltd was selected in our work. We build a reservoir model of 200ft long, 1000ft wide and 200 ft thick two 1-ft wide ×1000-ft long hydraulic fractures to simulate gas flooding and water flooding in shale oil reservoirs. We first validate a base model, and discussed the determination of miscibility parameter and injection pressure. Production behavior and oil recovery of different plans are discussed through sensitivity studies. Simulation results of primary production, gas injection and water injection are compared in this thesis. Results show that miscible gas injection has better effect on improving oil recovery from shale reservoirs than water injection. Solvent injected into the reservoirs above MMP can be fully miscible with oil, reducing oil viscosity greatly, and can lead a better sweep efficiency besides pressure maintenance. Our simulation results indicate that the oil recovery can be increased up to 15.1% by using gas injection in a hydraulically fractured shale reservoir, compared with the original 6.5% recovery from the primary depletion. This thesis provides a preliminary analysis to regarding the EOR potentials by gas and water flooding in shale oil reservoirs. The results show that miscible gas flooding could be a good prospect in future development of shale oil resources.