--> --> Improving the performance of mature waterfloods

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Improving the performance of mature waterfloods

Abstract

Communities of microbes live in many mature waterfloods, especially those producing heavier oils. The microbes gain their energy by breaking down portions of the oil to smaller molecules, ultimately to methane. This is a natural process, responsible for transforming lighter oils into basin-scale deposits of very heavy oil (examples: Orinoco (Venezuela) and Athabasca (Canada)), and also, on local scale, partially biodegrading the oils present in numerous oil reservoirs in many basins. The process can be made to work in commercial time by providing the microbes with chemical activators in dilute concentrations. Once stimulated, the microbes will produce methane gas. In conventional reservoir rocks, the new methane will serve as an effective and durable flow diversion agent, expanding the waterflood's swept zone and increasing oil recovery. Important biological aspects of this technology are its focus on stimulating native microbes, where they already live, without inoculation of any new microbes, and without significant modification of the oil reservoir's chemical environment. The science of DNA sequencing makes it possible to identify the proper activator formulation for a reservoir harboring appropriate microbial life. The chemical activators needed for the process are simple, and water soluble. In the field, they are easily blended into waterflood injection water in small quantities. Mechanical footprint is light, operational demands are minimal, and project screening criteria focus on geochemical and biological samples and waterflood operational history, rather than detailed lithologic and geostatistical data and models. In the field, oil production increases of 25% have been observed, at reserve costs in the range of $6/bbl new oil. This paper will describe the process; how it works at the pore level within mature waterflooded reservoirs; and its physical application in such fields.