Microbial Profile Modification With Spores
- J.H. Bae (Chevron Petroleum Technology Co.) | K.T. Chambers (Chevron Petroleum Technology Co.) | H.O. Lee (Chevron Petroleum Technology Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- August 1996
- Document Type
- Journal Paper
- 163 - 167
- 1996. Society of Petroleum Engineers
- 1.14 Casing and Cementing, 5.1 Reservoir Characterisation, 5.4.10 Microbial Methods, 1.6.9 Coring, Fishing, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.3.2 Multiphase Flow, 4.1.2 Separation and Treating, 2.2.2 Perforating
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To overcome the shortcomings of conventional, near-wellbore profile modification methods, a microbial profile modification method using spores was investigated. A halotolerant, spore-forming mesophile was isolated and characterized. These biopolymer-producing spores propagate easily in Berea cores with permeabilities more than about 500 md. With a specifically formulated nutrient package, they are readily germinated and produce biofilm, which reduces the permeability of the rock. The depth of penetration and the degree of permeability reduction can be controlled by varying injection schemes.
The use of microbes in enhanced oil recovery has been discussed for more than 40 years. The idea behind the microbial enhanced oil recovery (MEOR) is that microbes can produce most of the agents used in enhanced oil recovery. These include surfactants, polymers, solvents such as ethanol and aceton, acids, and gases such as CO2 and methane. Thus, it has been purported that these chemicals and gases produced in situ, alone or in combination, improve the oil displacement efficiency.
A flood of papers have been published in recent years on the laboratory investigations as well as field trials of MEOR, both in the US and abroad. Many technical meetings devoted exclusively to MEOR have been held, and the proceedings have been published. Unfortunately, many MEOR studies in the literature have been poorly designed, and the mechanisms of oil recovery have not been clearly delineated. Some were poorly documented and reported with many questionable claims. As a consequence, MEOR is received with much skepticism in the oil industry.
At the outset, we felt that, while MEOR is technically feasible, that is, microbes produce chemicals in situ, the chance of producing the right chemicals in the right amount to effect the desired results is rather slim. On the other hand, microbial profile modification (MPM) depends on in-situ biofilm formation. Biofilm is the multilayer growth of cells and support material on solid surfaces, consisting of biopolymer and biomass produced by the microorganisms. Thus, this process does not depend on delicate chemical systems produced by the microbes and is much easier to achieve the desired results.
As we conceptualized, this process could be used for in-depth treatments of high-permeability or thief zones. This method overcomes the shortcomings of the conventional treatments such as polymer gels, squeeze cementing, and selective perforation, whose effects are negated by crossflow in the reservoir. This process involves the injection of biopolymer-producing bacteria in the form of spores and nutrient package. This process relies upon injected microorganisms and nutrients to reduce the permeabilities of watered-out thief zones or high-permeability streaks by forming a resilient biofilm in the pore space of the reservoir rock.
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