When and Where Relative Permeability Modification Water-Shutoff Treatments Can Be Successfully Applied

Abstract

Summary This paper provides guidance on when and where relative-permeability-modification/disproportionate-permeability-reduction (RPM/DPR) water-shutoff (WSO) treatments can be successfully applied for use in either oil or gas production wells. When properly designed and executed, these treatments can be successfully applied to a limited range of oilfield excessive-water-production problems. When these treatments are applicable, they may be placed using bullhead injection (not requiring mechanical zone isolation)—a very favorable feature. However, there are a substantial number of limitations and possible pitfalls relating to the successful application of RPM/DPR WSO treatments. First-time application by an inexperienced operator should be considered a somewhat high-risk undertaking. In order to successfully treat unfractured production wells (i.e., radial flow through matrix rock into the well) that are fully drawn down, the oil and water zones should not be in pressure communication and the oil-producing zone(s) must be producing at 100% oil cut (dry oil). When treating unfractured and multizoned production wells that are not fully drawn down, the well's long-term oil-production rate can be increased if the post-treatment drawdown is increased substantially. Treatments that promote short-term (transient) decreased water/oil ratios can, in principle, be applied to many unfractured production wells (that are not totally watered out) in matrix-rock reservoirs. However, these latter treatments must be custom designed and engineered on a well-by-well basis. Furthermore, for most wells, the performance and the economics of such transient WSO treatments are generally marginal. An attractive application of RPM/DPR WSO treatments is the use of robust pore-filling gels in the matrix reservoir rock that is adjacent to a fracture(s) when oil and water is being co-produced into the treated fracture. Introduction RPM is a property that is exploited during certain oilfield WSO treatments, and a property whereby many water-soluble polymers and aqueous polymer gels reduce the permeability to water flow to a greater extent than to oil or gas flow. These are some of the many illustrative literature references (Sandiford 1964; White et al. 1973; Sparlin 1976; Weaver 1978; VanLandingham 1979; Schneider 1982; Kohler et al. 1983; Dunlap et al. 1986; Dovan and Hutchins 1994; Seright 1995; Stanley et al. 1997; Faber et al. 1998; Eoff et al. 2003a; Ligthelm 2001; Morgan et al. 2002; Di Lullo and Rae 2002; Eoff et al. 2003b; Kume 2003; Seright 2006; Pietrak et al. 2005) that discuss the RPM phenomenon. RPM WSO treatments are applicable to both oil and gas production wells. RPM is also referred to as disproportionate permeability reduction DPR. Some practitioners reserve the term "DPR" for relatively strong polymer gels that impart a large degree of disproportionate permeability reduction and a large reduction in water permeability. These practitioners reserve the term "RPM" for systems such as solutions of water-soluble polymers or relatively "weak" gels that impart more subtle disproportionate permeability reductions and more subtle reductions in water permeability. However, in this paper, the terms RPM and DPR will be considered synonyms. At times in the literature, DPR and RPM have also been referred to as "selective-permeability reduction" and "selective-permeability blocking." In this paper, the term "WSO treatment" refers to a chemical treatment that is applied (to an oil or gas producing reservoir) to either reduce or totally shutoff water production from a well. Historically, RPM/DPR is a phenomenon that was believed limited to fluid flow in matrix-rock porous media. More recently, it has been reported that certain relatively strong WSO gels impart RPM/DPR to fluid flow within gel-filled fractures (Sydansk et al. 2005). However, because such relatively strong gels also significantly reduce the permeability to oil flow in fractures, these gels are better characterized as total shutoff gels than as RPM/DPR WSO gels.