Optimization of operational strategies for rich gas enhanced oil recovery based on a pilot test in the Bakken tight oil reservoir

Horizontal well drilling and multistage hydraulic fracturing have been demonstrated as effective approaches for stimulating oil production in the Bakken tight oil reservoir.However,after multiple years of production,primary oil recovery in the Bakken is generally less than 10%of the estimated original oil in place.Gas huff‘n’puff(HnP)has been tested in the Bakken Formation as an enhanced oil recovery(EOR)method;however,most field pilot test results showed no significant incremental oil production.One of the factors affecting HnP EOR performance is premature gas breakthrough,which is one of the most critical issues observed in the field because of the presence of interwell fractures.Consequently,injected gas rapidly reaches adjacent production wells without contacting reservoir rock and increasing oil recovery.Proper conformance control is therefore needed to avoid early gas breakthrough and improve EOR performance.In this study,a rich gas EOR pilot in the Bakken was carefully analyzed to collect the essential reservoir and operational data.A simulation model with 16 wells was then developed to reproduce the production history and predict the EOR performance with and without conformance control.EOR operational strategies,including single-and multiple-well HnP,with different gas injection constraints were investigated.The simulation results of single-well HnP without conformance control showed that a rich gas injection rate of at least 10 MMscfd was needed to yield meaningful incremental oil production.The strategy of conformance control via water injection could significantly improve oil production in the HnP well,but injecting an excessive amount of water also leads to water breakthrough and loss of oil production in the offset wells.By analyzing the production performance of the wells individually,the arrangement of wells was optimized for multiple-well HnP EOR.The multiwell results showed that rich gas EOR could improve oil production up to 7.4%by employing conformance control strategies.Furthermore,replacing rich gas with propane as the injection gas could result in 14%of incremental oil production.

A new approach of CO_(2)separation by applying rapid expansion of supercritical CO_(2)rich natural gas

The previous methods for CO_(2)separation from CO_(2)rich natural gas led to expensive production costs.This work was implemented to overcome the problems utilizing a new approach economically.The cooling and rapid expansion processes were integrated for the CO_(2)separation from CO_(2)rich natural gas on the supercritical condition.The experimental apparatus was newly constructed to perform the experiments,and the results were simulated using a various equation of state.The result reveals that the inlet temperature of supercritical expansion diminished the outlet temperature and the gas condensed easily.The simulation indicated that the 70%CO_(2)in natural gas was condensed easier than 45%CO_(2).We found that the outlet temperature of
42C and the vapor fraction of 0.69 was attained at the CO_(2)composition of 70%.Besides,the pressure drop change influences the vapor fraction at various CO_(2)compositions.The vapor fraction under supercritical diminished significantly compared with the nonsupercritical condition.The expansion coefficient determined utilizing the equation of state escalates by the enhancement of expansion inlet temperature based on CO_(2)composition in natural gas.The acid gas equation of state was the perfect equation to estimate the expansion coefficient with the absolute average error of 4.83%.This work suggests that the CO_(2)separation from CO_(2)rich natural gas with the cooling and rapid expansion method promotes the new approach to overcome the disadvantages of previous methods.