Microbial EOR Technology Advancement: Case Studies of Successful Projects
Authors: Dietrich F.L. , Brown F.G. , Zhou Z.H. , Maure M.A. 
Published: December 2007

Abstract
Field results from five commercial Microbial EOR projects with diverse reservoir conditions prove Microbial EOR increases production and reserves while decreasing water cut. The projects are located in different geographical areas of the petroleum industry with two in the USA, one in Argentina and two in China. Included is a dolomite and four sandstone reservoirs with average permeability ranging from 1.7 to 300 md. Microbial reduced oil viscosity and residual oil result in improved oil recovery. Production rate increases range from ten to five hundred percent, averaging thirty-nine percent. Oil recovery increases thus far average thirty-two percent. Numerical simulator results considering the two main microbial effects are consistent with field performance.
On all five projects facultative anaerobic bacteria capable of deriving nourishment from the native reservoir environment are injected into the producing wells. The microbes are diluted with water and placed in the formation using annular batch treatments. Treatment size has ranged from ten to 450 barrels and frequency from every seven to twenty-eight days. Injection wells are treated as recycled produced water is injected. Microbe selection and effectiveness are determined and monitored by measuring changes in Newtonian behavior and viscosity of produced oil.

Introduction
Production data and laboratory results indicate microbes improved production and increased reserves on each of the five projects. Oil production rates are compared to baselines established by the operator before the start of Microbial EOR. Care was taken to continue field operations in the same manner under Microbial EOR as during the period the baseline was established. Laboratory testing for microbe induced oil viscosity decreases confirmed the effectiveness of the selected microbes both before and during the projects.
Microbes can improve oil recovery byGeneration of gases that increase reservoir pressure and reduce oil viscosity,Generation of acids that dissolve rock improving absolute permeability,Reducing permeability in channels thereby improving displacement conformance,Altering wettability,Producing bio-surfactants that decrease surface and interfacial tensions, andReducing oil viscosity by degrading long-chain saturated hydrocarbons.
For the reservoirs and microbes in these five projects, 4, 5 and 6 are considered the significant mechanisms for the reduction of residual oil and increased production. A typical reservoir was numerically simulated using three phase, black oil calculations. Considered in the simulator model are reduced oil viscosity, reduced residual oil and changes in relative permeability which occur as the microbes migrate or are transported through the reservoir. Model results are consistent with the field results.

Projects
The five projects listed in Table 1 represent a diverse geographic and geologic mixture. Two of the projects are in the USA, one is in Argentina and two are in the P. R. China. Lithology includes sandstone, fractured dolomite, siltstone/sandstone and fractured sandstone. Reservoir depths vary from 4450 to 6900 feet, net thickness from 18 to 60 feet, porosity from 0.079 to 0.232 and effective permeability from 1.7 to 300 md (Table 2). Reservoir temperatures range from 110 to 180 F and water salinities vary from 8,000 to 180,000 ppm chlorides, as shown on Table 3. All the projects are under waterflood. The five projects represent a wide range of reservoir and fluid properties as well as vastly different operating conditions and philosophies.
These five commercial projects have increased oil production by thirty-nine percent or six hundred barrels per day:
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