This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 132978, ’Quantitative Evaluation of Aquifer Diversion to Surrounding Wells After Multiple Large Polymer Gel Water Shutoff Treatments,’ by Ben Turner, SPE, Tiorco, and Jude Nwaozo, SPE, and Brad Funston, SPE, Marathon Oil Company, originally prepared for the 2010 SPE Production and Operations Conference and Exhibition, Tunis, Tunisia, 8-10 June. The paper has not been peer reviewed.
From April through August of 2009, seven producing wells in the Spring Creek field in the Big Horn basin of Wyoming were treated with chromium-acetate-crosslinked polyacrylamide in an attempt to reduce water production, lower fluid levels, and achieve greater drawdown, resulting in improved oil production. The wells were chosen because of their high productivity, high water cut, suboptimal operation because of pump limitations, and in some cases, marginal economics.
Introduction
The Spring Creek field is on the west flank of the Big Horn basin in Park County, Wyoming. Structurally, Spring Creek forms an asymmetrical anticline. The main oil reservoirs in Spring Creek are the Tensleep sandstone (Pennsylvanian) and the Phosphoria formation (Permian).
Both the Phosphoria and the Tensleep are connected to prolific aquifers that supply reservoir energy, but also supply a high rate of water. In most wells in the field, both formations are produced and commingled, but in many wells, the Tensleep is so productive that the well is limited in lifting capacity and the Phosporia has not been perforated. The well spacing in the field averages approximately 5 acres.
Strategy
The operator has an extensive history of shutting off water production by use of chromium-crosslinked polyacrylamide gels. By using chromium acetate as a delayed crosslinker for partially hydrolyzed polyacrylamide, a large volume (as much as 11,500 bbl in this case) can be injected and then allowed to cure for a week. When the gel cures, it reduces the permeability of the fracture and is able to withstand a high differential pressure such as that seen in the near-wellbore region of a producing well. The gel is bullheaded through tubing, with a packer set above the productive formations. Because of the large permeability difference between the fractures and the formation matrix, the gel will penetrate the fractures and significantly reduce the permeability, reducing the water production and fluid level, thus allowing the well to be pumped off and oil production to be increased. This technique has been used quite successfully in several hundred applications throughout the USA.
