A Novel Survey of Bulk Gel Treatment Designs in Injection Wells-Part I: Gel Strength

Abstract

Polymer bulk gels are increasingly applied to alleviate the costly burden of excessive water production in mature oil fields. This paper presents a comprehensive review of the designs of injection well gel treatments conducted between 1985 and 2014. The survey includes 61 field projects compiled from SPE papers and U.S. DOE reports. Seven design parameters related to the gel strength were evaluated per the reservoir type and the recovery process using the univariate descriptive analysis and stacked histograms. We identified that there is a great concern about losing the informative content of the three levelsdata of gel treatment designs unless a specialized data reporting approach is used to obtain sufficiently representative and discriminating field-wide estimations. The traditional practice to plan a gel treatment is to adopt the designs from gel case histories in similar formations or empirically estimated the designs by reservoir engineers. The gel strength parameters are appreciably affected by the formation type and reservoir types can be ordered in term of increasing polymer concentration as matrix-rock, unconsolidated, and naturally-fractured. Gel treatments typically start with polymer concentration of 3000 ppm, end with 7600 ppm, and a constant polymer-crosslinker ratio of 40:1 is maintained during the treatments. Often, gel treatments are applied using polymers of 10-11 MM Dalton molecular weights that are injected in three to five treatment stages. The gel strength is designed based on the problem channeling strength and the required gel volume. However, in the cases of void-space problems, gel extrusion, gel breakthrough, and gel breakdown become important designing criteria. To address these issues, more advanced tapering schemes than the normal gradual increase of polymer concentrations are used to optimize the gel plugging efficiency. In addition, small volumes of cement or low molecular weight, fast-maturing, rigid gels are injected in front (only gels) or behind the MARCITSM gels as capping materials. The unsuccessful gel pilots had significantly higher polymer concentrations than the successful gel projects applied in the same formation type. Increasing trends were identified of polymer concentrations against the treatment timing indicators. The present review prominently maintains the variability of the design data and provides conformance engineers with the typical treatment designs for different application environments.