Simulation and Optimization of CO2 Huff-and-Puff Processes in Tight Oil Reservoirs

Abstract

As one of the unconventional resources, tight oil has become one of the most important contributor of oil reserves and production growth. The successful commercial production of tight oil is mainly reliant on the advancement in horizontal drilling and multistage hydraulic fracturing technique. Development of tight oil reservoirs remains in an early stage. Primary oil recovery factor in these reservoirs is very low, leaving substantial volume of oil trapped underground due to the low porosity, low permeability characteristic of tight oil reservoirs. Thus, investigation of enhanced oil recovery methods is more than imperative in tight oil reservoirs. CO 2 Huff-and-Puff technology has been effectively applied in conventional reservoirs and can be tailored to adapt for the characteristics of tight oil reservoirs.In this study, the performance of water flooding in tight oil reservoir is studied and compared with that of the CO 2 Huff-and-Puff process. Sensitivity analysis demonstrates that the performance of CO 2 Huff-and-Puff is more sensitive to the length of gas injection and production step in each cycle, compared to the soaking time. The CO 2 Huff-and-Puff process is optimized and an adaptive CO 2 Huff-and-Puff process is conducted for tight oil reservoirs after primary production. Simulation results show that the adaptive cycle length CO 2 Huff-and-Puff process can improve the incremental oil recovery by 11.1% over a fixed cycle length process. Finally, the inter-well interference during CO 2 Huff-and-Puff is studied, and it is found that a multi-well asynchronous CO 2 Huff-and-Puff pattern can improve the incremental oil recovery by 31.6% over that of a synchronous pattern.

Huff-n-Puff Technology for Enhanced Oil Recovery in Shale/Tight Oil Reservoirs: Progress, Gaps, and Perspectives

“…Because of the difficulties of maintaining a proper contact between injection and extraction wells in fractured shale beds, multiple-well cyclic injection is seldom used. However, in some situations, when conducted asynchronously with multiple parallel wells to have favorable interwell interruption, the method may be far more efficient than H-n-P in individual wells . The multiwell cyclic injection is performed on a laboratory scale by injecting gas into one end of a confined container that houses the core sample, leaving the gas to soak with a saturated core for a predetermined time, and then producing from the other end of the core holder (Figure b).…”

“…However, in some situations, when conducted asynchronously with multiple parallel wells to have favorable interwell interruption, the method may be far more efficient than H-n-P in individual wells. 133 The multiwell cyclic injection is performed on a laboratory scale by injecting gas into one end of a confined container that houses the core sample, leaving the gas to soak with a saturated core for a predetermined time, and then producing from the other end of the core holder (Figure 14b). The use of a core holder with two ends (inlet and outlet) is not possible, because of the low permeability of shale plugs.…”

Mechanisms and capacity of high-pressure soaking after hydraulic fracturing in tight/shale oil reservoirs

“…In some oilfields, water flooding has been conducted. However, if the well spacing is larger, the producers are not responding under a very high injection pressure (Song and Yang 2013;Kong et al 2016;Mansour et al 2017). Conversely, if the well spacing is smaller, water channels faster to the producers through the hydraulic fractures (Thomas et al 2014;Li et al 2015;Pourabdollah 2018).…”

Exploitation of fractured shale oil resources by cyclic CO2 injection

“…The sensitivity analyses show that short injection and production periods were favorable for CO 2 huff-n-puff performance. A series of sensitivity studies of CO 2 huff-npuff EOR in shale oil reservoirs was examined (Alfarge et al 2017b;Kong et al 2016;Sheng 2015;Yu et al 2014). The simulation results show that the most influential variables are injection time, CO 2 injection rate and the number of cycles employed.…”