Evaluation of Waterflood Operations at Iatan East Howard Field, Mitchell County, Texas

David P. Smith, Steven M. Mitchell

Mobil Exploration and Producing U.S. Inc. completed a reservoir description study on Iatan East Howard field in Mitchell County, Texas, in 1984. The application of study results has improved subsequent development drilling and waterflood operations. Lease production has doubled within two years with the drilling of 40 producers and 13 injection wells. The field produces from thin (2 to 40 ft) porosity stringers in fractured Permian age San Angelo and Clearfork dolomites at 2,300 to 3,200 ft in depth. Reservoirs are areally discontinuous due to original depositional controls on porosity development and distribution. Pay zone reservoir parameters such as porosity and permeability vary from 4 to 17% and 0.1 to 120 md, respectively. The presence of a fracture orientation at N 0°E to N85°E has caused producing wells to experience early breakthrough of injection water when in line with injectors and the fracture direction. Waterflows have also occurred in drilling wells when similarly aligned. Recognition of this fracture overprint has dictated the use of a staggered line drive injection pattern parallel to the fracture trend to improve sweep efficiency. Reservoir matrix can be swept more uniformly as rows of injectors pressurize those aligned fractures and move oil perpendicular to the fracture trend and toward the rows of producers. Certain injectors will be targeted specifically for highly productive individual pay zones and will influence pattern alignment.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.