Enhanced Oil Recovery in Liquid–Rich Shale Reservoirs: Laboratory to Field

Abstract

Summary Production of tight oil from shale reservoirs in North America reduces oil imports and has better economics than natural gas. Currently, there is a strong interest in oil production from Bakken, Eagle Ford, Niobrara, and other tight formations. However, oil-recovery fraction for Bakken remains low, which is approximately 4–6% of the oil in place. Even with this low oil-recovery fraction, a recent United States Geological Survey study stated that the Bakken and Three Forks recoverable reserves are estimated to be 7.4 billion bbl; thus, a large volume of oil will remain unrecovered, which was the motivation to investigate the feasibility of enhanced oil recovery (EOR) in liquid-rich shale reservoirs such as Bakken. In this paper, we will present both laboratory and numerical modeling of EOR in Bakken cores by use of carbon dioxide (CO2), methane/ethane-solvent mixture (C1/C2), and nitrogen (N2). The laboratory experiments were conducted at the Energy and Environmental Research Center (EERC). The experiments recovered 90+% oil from several Middle Bakken cores and nearly 40% from Lower Bakken cores. To decipher the oil-recovery mechanisms in the experiments, a numerical compositional model was constructed to match laboratory-oil-recovery results. We concluded that solvent injection mobilizes matrix oil by miscible mixing and solvent extraction in a narrow region near the fracture/matrix interface, thus promoting countercurrent flow of oil from the matrix instead of oil displacement through the matrix. Specifically, compositional-modeling results indicate that the main oil-recovery mechanism is miscible oil extraction at the matrix/fracture interface region. However, the controlling factors include repressurization, oil swelling, viscosity and interfacial-tension (IFT) reduction, diffusion/advection mass transfer, and wettability alteration. We scaled up laboratory results to field applications by means of a compositional numerical model. For field applications, we resorted to the huff ’n’ puff protocol to assess the EOR potential for a North Dakota Middle Bakken well. We concluded that long soak times yield only a small amount of additional oil compared with short soak times, and reinjecting wet gas, composed of C1, C2, C3, and C4+, produces nearly as much oil as CO2 injection.

Evaluation of Cyclic Gas Injection in Enhanced Recovery from Unconventional Light Oil Reservoirs: Effect of Gas Type and Fracture Spacing

“…The molecular diffusion coefficients of CO 2 , ethane and natural gas used in this model are set to 5.5 × 10 −4 , 4 × 10 −4 and 6 × 10 −4 cm 2 /s, respectively [13,14]. As mentioned, in the field scale studies of cyclic gas injection process, normally the operation continues for a certain number of fixed-size cycles.…”

“…After the soaking period, the well is put into production for a specific time and the whole procedure is repeated. Simulations of the cyclic CO 2 -injection method in Bakken have demonstrated incremental [13] oil recoveries between 5% to 20% in multistage hydraulically fractured wells [14]. Results from CO 2 extraction experiments on Upper and Lower Bakken core plugs also indicated that CO 2 diffusion under miscible conditions lowers the oil viscosity and makes the oil extraction from tight cores feasible [15].…”

A simplified method for experimentally quantifying crude oil swelling during immiscible carbon dioxide injection

“…Several experiments have been conducted to study CO 2 interaction with oil and its ability to increase oil recovery during immiscible CO 2 injection (Tran et al 2019;Hao et al 2019;Alharthy et al 2018;Mahzari. et al 2019;Sanaei et al 2018;Fakher and Imqam 2020, b, c, d; Hoffman and Rutledge 2019).…”

An experimental investigation to consider thermal methods efficiency on oil recovery enhancement

“…Approximately most of the volume of 1012 m 3 of the remaining crude oil (especially heavy oil) would be extracted via enhanced oil recovery (EOR) or improved oil recovery (IOR) techniques. The selection of recovery methods would be dependent on the reservoir and rock characteristics, economical and technical aspects of the proposed methods, corrosion issues, etc, which should be taken into consideration before operational performances to virtually eliminate the extra expenses of production operations 8‐11 . IOR is considered as a general concept to increase the oil recovery by the operational strategies, vertical sweep efficiency, and so on, however, EOR is related to the technical and explicit methods that are considered as the subset for IOR methods 12‐14 .…”