F.J. Lucia, D.G. Bebout, C.R. Hocott, G.E. Fogg, & G.W. Vander Stoep, The University of Texas
A significant available resource of unrecovered mobile oil resides within Grayburg reservoirs as a result of low ultimate recoveries of less than 30 percent of the large estimated volume of original oil in place. This low ultimate recovery from conventional primary and secondary recovery methods is due mainly to the heterogeneity typical of these reservoirs. Evidence of this heterogeneity is well displayed in the Dune field by significant production inequalities, particularly within the Mobil University Unit 15/16. The cumulative production from Section 15 is about 10 million barrels, whereas that from Section 16 is only 2 million barrels. This difference between the two adjacent sections cannot be attributed solely to varying production practices, but rather to major changes in rock fabric and depositional facies. Within Section 15, wells from the same reservoir have yielded widely varying amounts of total production, further demonstrating even smaller scale heterogeneity.