Field design guidelines for gel strengths of profile-control gel treatments based on reservoir type

Bulk gels are increasingly applied to alleviate the costly burden of excessive water production in mature oil fields. Practically, designs of new treatments are adopted from previous field projects conducted in analogous reservoirs. This case-finding procedure requires reservoir engineers to have thorough knowledge about how gel treatments, for each reservoir type, should be designed and have been mostly applied. This paper presents comprehensive design guidelines for injection-well gel treatments based on 61 worldwide field projects. It also assesses typical and most-applied designs and introduces them as new designing strategy. Seven gel strength design parameters were evaluated using the univariate descriptive analysis, stacked histograms, and scatterplots. Results indicated that gel strength parameters have very wide ranges and are considerably affected by the formation type. Gel treatments typically start with 3000 ppm polymer concentration, end with 7600 ppm, and a constant polymer-crosslinker ratio (PCR) of 40:1 is maintained during the treatments. They are often performed using the injection waters (to avoid type II gel syneresis) and polymers of 10-11 MM Da molecular weight (MW) and 30% hydrolysis that are injected in 4-5 treatment stages. The gel strength is principally designed based on the problem channeling strength and the planned gel volume. However, in cases of void-space-type problems, the gel extrusion, breakthrough, and breakdown become important designing criteria. To address these issues, more advanced tapering schemes than normal gradual increase of polymer concentrations are used to optimize gel plugging efficiency. In these schemes, small volumes of cement or low MW, fast-maturing, rigid gels (i.e., MARA-SEAL (TM)) are injected in front (gels only) or behind the high-MW MARCITsm gels as capping-materials. The novelty of present review lies in providing conformance specialists with new design strategy that would markedly facilitate designing of gel treatments and save time needed to identify analogs for a given candidate reservoir.