Alternative Methods for Permeability Modification Using Biotechnology
Authors: Stepp A.K. , Bailey S.A. , Bryant R.S. , Evans D.B. 
Published: December 2007

Abstract
Permeability modification is a useful technology for extending the productive life of watered-out oil fields. Polymers are widely used to decrease permeability of high permeability zones or water channels that form in heterogeneous petroleum reservoirs. Decreasing permeability of these previously swept zones diverts injected fluids into unswept regions of the reservoir, increasing the sweep efficiency and extending the production life of marginal fields. Many of the gelled polymers that have been developed for this purpose rely on toxic reagents and are environmentally unfavorable. Microbial polymer systems offer low cost, environmentally safe methods to produce polymer gels in situ. Several microbially controlled polymer systems are being developed to provide in depth permeability modification in heterogeneous reservoirs. One system uses polymer-producing bacteria to produce polymer biomass in situ. Another microbial method under development is a novel gelled polymer system that uses microorganisms to cause delayed gelation of an ex-situ produced biopolymer. This paper presents laboratory results from the microbial systems.

Introduction
Applying permeability modification treatments can significantly extend the productive lives of active oil recovery projects, curtailing the prospect of premature abandonment. Effective modification of reservoir sweep can improve the economics of an oil recovery process. The National Energy Strategy-Advanced Oil Recovery Program has identified permeability modification as an improved oil recovery (IOR) method having significant potential to arrest the current high rate of well abandonment.
Efforts to develop methods for permeability modification stem from the need to improve the efficiency of applied recovery methods such as waterflooding. Inherent reservoir characteristics can significantly impact field production. Current state-of-the-art technology in this area uses crosslinked polymer technology to alleviate problems associated with reservoir heterogeneity. Treatments in both injection and production wells have been applied. Limitations of technology are being addressed by continued research efforts in the area, but many of the current applications still rely on the use of crosslinking agents that may pose an environmental hazard. This paper addresses the development of alternative methods using biotechnology for permeability modification.
One of the microbial technologies under development uses microbial metabolism to trigger gelation of an ex-situ produced biopolymer. Curdlan biopolymer exhibits a pH-dependent reversible solubility, being soluble in alkaline solutions (pH &gt;10) and insoluble in neutral or acidic solutions. A similar polymer has been tested for permeability reduction using a layered process of alternating injections of alkaline-soluble polymer and neutralizing acid. The curdlan microbial gelation process described here places the polymer gelation process under the control of acid-producing bacteria. Another microbial process for permeability reduction uses bacteria to produce polymer in situ. The bacteria are injected into porous media and then stimulated to produce permeability-modifying biopolymer. Experimental studies were conducted to evaluate the effectiveness of these methods for permeability modification.
P. 649