Abstract

In the US, the development of shale & tight (unconventional) resources has been playing a critical role in domestic energy independence due to the vast resources, maturity of the technologies, short investment cycles and favorable geopolitical locations. Current shale & tight resource development focuses on primary depletion utilizing the initial reservoir energy to drive oil through complex fracture networks created through hydraulically fractured completions. Even though solution gas drive is an effective primary depletion mechanism, it can produce a small fraction of the original oil and leaves the majority of oil in the depleted formation, which provides great opportunities for secondary processes, such as gas injection.

This paper presents a systematic effort maturing gas injection as a EOR (enhanced oil recovery) process for shale & tight resources development. We first quantified the major mass transfer mechanisms in the laboratory and estimated their potential relative contributions to mixing of oil and gas in the complex networks of fractures and matrix through conceptual models. A pilot has been designed and executed in the Midland Basin for proof of concept. The pilot results confirmed the major recovery mechanisms with quantifiable EOR responses.

Introduction

Over the past decade, technological advances in horizontal drilling and hydraulic fracturing have allowed access to large volumes of shale oil that were previously uneconomic. The U.S. Energy Information Administration (EIA) estimates that in 2021, about 7.23 million barrels per day of crude oil were produced directly from shale & tight (S&T) oil resources in the United States, suggesting huge resource base for asset valuation enhancement. One of the major characteristics of shale & tight resources development is the fast initial production declines. To sustain production, one needs new development resources and investment for drilling, completion, and facilities, while the facilities in the "developed" areas become underutilized due to the fast production declines. Hydrocarbon gas injection could be a potential game changer for valuation enhancement of unconventional assets by improving oil recovery with little additional facility investment. The concept of gas injection for shale & tight is not new, and many papers have been published on earlier laboratory testing (B. Haghshenas, et al. 2017, M. Akbarabadi, et al. 2023), simulation studies and pilot reports (T. Hoffman, 2018). Data reported from Eagle Ford pilots showed substantial incremental oil from hydrocarbon gas injection (T. Hoffman, et al. 2019, G. Grinestaff, et al. 2020, G. Pospisil, et al. 2020, Rogers, et al. 2020). However, data reported from pilots in other areas are mixed. In this paper, we aim to close the current gaps in the literature by presenting a systematic effort leading to the design and execution of a hydrocarbon gas injection pilot for the proof of concept in the Permian Basin. Let’s first start with quantification of recovery mechanisms.

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