New opportunities in the mature fields of the central Illinois Basin: a case study of the Mode field, Shelby County, IL, USA

Abstract

Wells that produce less than 10 barrels of oil per day account for up to 96% of the Illinois Basin’s (ILB) total production. Little has been done to study the potential exploitation of unswept mobile or immobile oil through improved recovery in the Illinois Basin in a systematic field-by-field study. Department of Energy (DOE) data resource appraisals indicate that 2 billion barrels of bypassed mobile oil and more than 5.4 billion barrels of immobile oil are potential targets for future exploitation in the Illinois Basin. Heterogeneities in the basin’s reservoirs and standardized well spacing account for the failure to produce this otherwise mobile oil. This Master’s Thesis helps to better understand the opportunities that mature fields of the Southern Illinois Basin provide to produce new resources. Mode field in the central ILB is chosen as a typical marginal field that has produced around 440,000 bbls of oil to date and has estimated remaining recoverable reserves of over 970,000 bbls of oil. This study looks at the structural and stratigraphic nature of reservoirs and seals, the economic value of the field and establishes a basis of comparison for other mature fields in the ILB. The present reservoir targets are the Bethel, Benoist (Yankeetown), and Aux Vases Sandstones, however, reservoir heterogeneities require the use of new technology and new approaches to well placement to remobilize unswept oil to enhance long-term production. New opportunities for missed pay, deeper reservoir existence, and source-rock reservoir plays in the New Albany shale are also analyzed for additional oil recovery. The result of this work helps to better understand the data needs, knowledge needs and economic needs to recover future reserves in these ILB marginal fields.