Improved oil recovery from the Aux Vases (Mississippian) Formation at Boyd Field, Jefferson County, Illinois

Oil production at Boyd Field in Jefferson County, Illinois, is structurally and stratigraphically controlled. The field has 20 feet of anticlinal closure and is 2 1/2 miles long and 1 mile wide. The Aux Vases Formation at Boyd Field is approximately 40 feet thick. The reservoir sand occurs in the uppermost 20 feet of the formation and is typically limited in areal extent. Most of the wells that produce from the Aux Vases also were completed to produce from the Benoist reservoir. The Benoist reservoir has an active water drive and shows less pressure decline than the Aux Vases reservoir, which is a gas-solution drive. Pores in the Aux Vases reservoir are lined by a mixture of three types of clay minerals: mixed-layered illite/smectite, illite, and iron-rich chlorite. The mixed-layered illite/smectite can swell in freshwater, clog pore throats, and reduce permeability by more than 50%. An understanding of the original reservoir management practices, in conjunction with detailed reservoir characterization, may allow operators to recover a greater percentage of the remaining mobile reserves. -from Author