Combined Microbial Surfactant-anPolymer System for Improved Oil Mobility and Conformance Control

Abstract

ABSTRACT Microbial enhanced oil recovery (MEOR) technologies have become established as cost-effective solutions for declining oil production. The demonstrated versatility of microorganisms can be used to design advanced microbial systems to treat multiple production problems in complex, heterogeneous reservoirs. This research project presents the concept of a combined microbial surfactant-polymer system for advanced oil recovery. The surfactant-polymer system utilizes bacteria that are capable of both biosurfactant production and metabolically-controlled biopolymer production. This article describes the results of our laboratory work to grow microbial cultures and the work done on recovery experiments on core rocks. A bacterial strain capable of producing both surfactant and polymers has been selected. Laboratory experiments to determine under what conditions surfactants and polymers can be produced from one single strain have been conducted. Recovery experiments to determine the performance of these strains under different conditions have been carried out. Experimental results show a significant influence of nutrient regime on alternate production of surfactants or polymers for a Bacilluslicheniformis strain, NIPER 1A. INTRODUCTION Microbial Enhanced Oil Recovery (MEOR) is an EOR method that uses microorganisms and their metabolic products to improve oil production in the reservoir. The majority of the MEOR work leading to field trials has been completed in the last 20 years. The technology has advanced from a laboratory-based evaluation of microbial processes, to field applications internationally. MEOR has been recognized as a potentially cost-effective method, particularly for stripper wells (well that produces less than 10 bbl/day)1. The first suggestion for using MEOR was made as early as in 1926, when Beckman reported the action of bacteria on mineral oil2. As a result of his work, he proposed that bacterial enzymes could be used in oil recovery. However, little work was done until ZoBell started a series of systematic laboratory investigations in the 1940's in connection with the American Petroleum Institute3,4. In this study we concentrated on microbial enhanced waterflooding. MEOR is applied to existing waterfloods to improve their performance and enhance oil production by treating the entire reservoir. The microorganisms play various roles in the reservoir. The most important ones considered in this project are: production of surfactants, selective plugging of the reservoir and polymer production5. Microorganisms can produce surfactants that can decrease surface and oil-water interfacial tension to as low as 5*10-3 mN/m6. Interfacial tension between oil and water is normally about 10 mN /m6. In general, a biosurfactant is easily dissolved in connate water or injection water and acts favorable on the interface between oil and water. Interfacial tension reduction decreases the pressure required to release oil trapped in the rock pores by capillary forces, which displaces oil from the pores into the mobile liquid phase. Microbial biosurfactants usually act in the same way as synthetic surfactants, and have the same characteristics6. Another application for microorganisms in a waterflood is fluid diversion. Since many types of microorganisms produce polymers, biomass, and slimes, it has been suggested that some microorganisms could be used in-situ to preferentially plug high permeability zones in the reservoir, and thus improve sweep efficiency7,8.