Enhanced Recovery Technologies for Unconventional Oil Reservoirs

Abstract

Management Unconventional resources have transformed the landscape of the oil and gas industry. The primary oil recovery factor ranges from 2–8% for the various shale plays throughout the US. Hence, it is imperative to develop the vast potential of unconventional reservoirs and increase the recovery factors beyond primary depletion by implementing IOR/EOR methods. This article describes the role of effective reservoir management and summarizes the detailed review of the advances in IOR/EOR technologies applied to unconventional oil reservoirs, as performed by the Energy Industry Partnership Team (EIP) at the University of Houston (Balasubramanian et al. 2018). That review•included: A thorough review of the pertinent published literature on IOR/EOR Results of EOR application to unconventionals shared by various operators in their investor presentations and from press reports Classifying IOR/EOR studies as laboratory experiments, numerical modeling, and field laboratory trials•(pilots) Analysis of field trials based on the representative shale plays. Most studies performed for the application of EOR technologies to unconventional oil reservoirs have been limited to experimental investigations and numerical simulation studies. The research revealed that miscible gas injection (produced field gases, CO2, etc.) is the most promising method among the EOR techniques, including miscible gas, waterflooding, surfactant, chemical, and polymer. Experimental studies showed the following: CO2 injection had the highest potential of improved recovery in unconventionals followed by produced gas injection. Surfactant injection showed the next best potential to increase oil recovery by altering the wettability of rock in laboratory experiments. The produced field gas injection pilots showed that sufficient injectivity was achieved mainly due to the injection-induced fractures and did not exhibit any significant effect of diffusion. Conformance control remains a big challenge due to the channeling of the gas through the fractures. Produced field gas injection pilots in the Eagle Ford formation have demonstrated the greatest success in increasing oil recovery. Many inconsistencies exist between laboratory investigations and field trials that need reconciliation and further research to bridge the gap. This methodical study elicits the learnings and challenges from the application of different IOR/EOR technologies to unconventionals at various scales (micro to macro to field scale). In addition, ideas for future research are recommended to improve the understanding of the complex mechanisms of EOR in unconventional oil reservoirs. Unconventional resources have changed the landscape of oil and gas industry in the US and the world. Oil production from unconventional tight oil reservoirs have accounted for more than 50% of total oil production in the US in the recent years. Todd et al. reported that unconventional oil reservoirs contributed to more than a 4 million•B/D increase in production between 2011 and•2014.

Investigating Enhanced Oil Recovery in Unconventional Reservoirs Based on Field Case Review, Laboratory, and Simulation Studies

“…Based on a detailed literature survey and communications with field operators, 24 EOR pilot tests performed in North American unconventional plays were identified. The EOR-related data was collected from a variety of sources, including publications and governmental databases available through the North Dakota Industrial Commission (NDIC), Texas Railroad Commission (TRC), and oil and gas companies. ,− General information on these 24 pilot tests is summarized in Tables and .…”

“…These tests showed that fluid injectivity in unconventional reservoirs may not be an issue because of the existing fractures in the formations. However, the conformance issues caused by hydraulic fractures and the interconnected fracture network within the stimulated reservoir volume were the main challenges to achieving a significant EOR response in most of the pilot tests. − …”

“…Reservoir simulation is one of the most widely used tools for EOR investigation in the oil and gas industry, especially for well- or field-scale studies. Because well interference was observed in almost all of the gas injection EOR pilots and was considered one of the most critical challenges for EOR operations in unconventional reservoirs, − a multiple-well multiple-fracture (MWMF) simulation model was employed to evaluate the feasibility of performing rich gas EOR in a Bakken oil field. , The model used an equation-of-state (EOS) with eight components to ensure a variety of gas injection scenarios can be simulated. Figure shows the simulation model integrated with fractures created by the embedded discrete fracture model (EDFM) method.…”

“…only marginal or little incremental oil production was observed in the field after performing EOR operations). Conformance issues caused by well interference were identified as one of the most critical challenges in the gas injection process due to the massively interconnected fractures between wells. − …”

Could China meet its emission reduction goal by CO2-EOR

“…A lot of scientific publications have addressed the feasibility of the CO 2 -EOR application (Ampomah et al , 2017; Font-Palma et al , 2016; Verma, 2015; Lu et al , 2018; Thakur, 2019). Most attention has focused on the economics solely such as CO 2 capture and compression, CO 2 transportation and CO 2 injection and storage costs (Welkenhuysen et al , 2017; Wei et al , 2015; Welkenhuysen et al , 2018; Wright, 2018; Meng et al , 2016).…”