Eldon Dwyann Dalrymple

Effect of relative-permeability modifier treatments in a sandstone-layered system and in a sandstone-homogeneous system

By using chemical treatments in attempts to reduce the volumes of water produced from hydrocarbon-bearing strata, well operators face the risk of damaging productive intervals. To avert this problem, well operators often apply special placement techniques (such as the use of the dual-injection technique and multiple-packer assemblies) in attempts to focus water shutoff treatments into areas of interest. The special placement techniques require significant additional costs involving workover rigs, coiled-tubing units, multiple pumping units, tools, packers, and so on. Even when these precautions are taken, the chemical treatment may still enter the productive interval through any number ofavenues, including interzonal communication, packer leaks, or channels behind the pipe. The oil and gas industry is inherently attracted to relative-permeability modifiers (RPMs) because they have the potential to reduce the relative risk factors involved when conformance water-management treatments are performed on active, hydrocarbon-producing wells. The term RPM has been misused at times by being used to refer to porosity-fill sealants (such as metal-complexed polyacrylamide systems). Although organic, water-based systems may preferentially achieve deeper penetration into water-saturated strata than into hydrocarbon strata, those systems still result in the forming of sealants. The ideal RPM should reduce the effective permeability to water with no effect on the effective permeability to oil. The RPM materials available to the industry today are not ideal. These materials actually affect the effective permeability to both water and oil. The difference between an RPM and a sealant is that the RPM reduces the effective permeability to water more significantly than the effective permeability to oil. This paper discusses the results of testing two currently available RPMs through porous rock media. The testing includes evaluation of the RPMs in a layered system (high-permeability streaks of water through hydrocarbon-bearing strata) and evaluation of the RPMs in a homogeneous system with varying degrees of water saturation (transition zone between oil- and water-bearing strata).