Further Discuss the Roles of Soaking Time and Pressure Depletion Rate in Gas Huff-n-Puff Process in Fractured Liquid-Rich Shale Reservoirs

Abstract

Cyclic gas injection (CGI), also known as huff-n-puff process, has been demonstrated as the most effective and promising IOR solution in shale reservoirs. Such process involves many operating parameters that can affect the recovery performance in different degrees. As soaking time and pressure depletion rate (PDR) are the two crucial factors, this study aims to further investigate their roles in the oil recovery process of CGI experimentally and numerically. A total of ten series of the N2 huff-n-puff tests were performed on oil-saturated Eagle Ford shale plugs in a matrix-fracture system. With the injection pressure (Pin) of 1,000 psi, two groups of tests were conducted: 1) under a constant PDR in blowout and five soaking times changed from 0.25-hr to 48-hr; 2) under a constant soaking time of 12-hr and four pressure depletion times changed from 0.05-hr to 48-hr. With the Pin of 5,000 psi, the CGI tests were performed under 12-hr soaking time and blowout pressure depletion to study the effect of Pin on recovery efficiency. Lab-scale simulation models were built and tuned to history match the experimental data. The experimental results show that recovery factor (RF) from a single cycle increases with soaking time within a certain range, and a longer time has no effect on improving oil recovery. For 1,000 psi Pin, during the soaking phase, the system pressure declined rapidly at the first 3 hr and then became stabilized. The pressure drop was relatively low (10 psi) in the first cycle compared with the following cycles. It tended to increase with the number of cycles performed, which was caused by the decrease of oil saturation thus more gas can be injected into the core sample. It reveals that a soaking period is necessary to the oil recovery process. On the other hand, increasing the pressure depletion rate can raise the incremental RF from each cycle. The blowout condition showed the highest cumulative RF. The performance of N2 huff-n-puff with 5,000 psi Pin outperforms the case of 1,000 psi, which can increase the ultimate RF with less cycles. The well-tuned simulation models were used to analyze and optimize the CGI recovery process.

Numerical analysis of cyclic CH4 injection in liquid-rich shale reservoirs based on the experiments using different-diameter shale cores and crude oil

“…The experiment injection pressure is chosen after considering the safety factor and experiment equipment capability. After analyzing other researchers' work in shale cores (Gamadi et al, 2013(Gamadi et al, , 2014a(Gamadi et al, , 2014bYu et al, 2016), the choice of pressure 2000 psi is a feasible pressure and can be used to test the effectiveness of gas cyclic injection EOR in shale oil cores. Table 1 includes the recovery factors of cyclic CH 4 injection for shale cores at different core sizes with the same length of 2 inches and different diameters of 1, 1.5, 2, 3, 3.5 and 4 inches.…”

“…After setting up the model, it is really important to validate the model with experiment data in order to make sure the simulation model is correct. The history match method used in this study is to tune the model input parameters including the shale matrix permeability, matrix porosity, fracture permeability within an acceptable range and adjust the relative permeability curves based upon the relative permeability curves generated in the previous shale oil reservoir simulation studies (Wan et al, 2013(Wan et al, , 2015(Wan et al, , 2016Yu et al, 2014aYu et al, , 2014bYu et al, 2016). The results for the oil recovery factor are shown in Fig.…”

Experimental investigation of shale oil recovery from Qianjiang core samples by the CO2 huff-n-puff EOR method

“…31 further explored the inuences of soaking time and consumption time on fracture-matrix shale reservoirs in huff and puff experiments using N 2 . 32 Li et al (2019) conducted experiments comparing the effect of N 2 and CO 2 on EOR performance, verifying the great potential of CO 2 in improving shale oil recovery. 33 Other researchers use commercial soware such as CMG and Eclipse to simulate the process of CO 2 HnP, and investigated the inuences of parameters including pressure, injection rate, gas diffusivity, soaking time, and fractures on the efficiency of HnP EOR.…”

Investigation of CO2/N2 injection in tight oil reservoirs with confinement effect

“…Because of its poor solubility in the oil, the positive effect of oil swelling due to N 2 dissolution is minimal. While nitrogen gas has good elastic energy during the flooding to maintain the reservoir pressure 1,[26][27][28][29][30] and has other advantages, such as its abundance in atmosphere, relatively low-cost and well-established harnessing/capture technology, and its noncorrosive property. 31 This makes nitrogen gas another significant gas candidate to improve tight oil reservoirs.…”