Gary E. Jenneman

Experimental Studies of In-Situ Microbial Enhanced Oil Recovery

Experiments were conducted to study the feasibility of using microorganisms in EOR, particularly for the correction of permeability variation. The use of microorganisms requires the ability to transport viable cells as well as the nutrients required for cellular growth through reservoir formations. Nutrients such as glucose, peptone-protein, and phosphate and ammonium ions were transported through brine-saturated Berea sandstone cores in amounts sufficient to support microbial growth. Viable bacterial cells were transported through sandstone cores of 170-md permeability. Less than 1% of the influent cell concentration was recovered in the effluent, indicating a high degree of cell retention inside the core. The addition of nutrients to these cores and subsequent incubation to allow for microbial growth resulted in permeability reductions of 60 to 80%. These data show that the growth of microorganisms significantly reduces the permeability of porous rock.

Selectivity and depth of microbial plugging in Berea sandstone cores

SummaryThe depth of plugging by the in situ growth of either injected or indigenous microorganisms was investigated using Berea sandstone cores with pressure taps located along the length of the core. The continuous injection of aerobically prepared sucrose-mineral salts medium with 5% NaCl and 0.1% NaNO3 resulted in large permeability reductions (70–98%). The plugging was localized at the inlet and outlet faces of the cores, and was attributed to microbial biomass production at the inlet face and biogas accumulation at the outlet face. Batch addition of aerobic medium resulted in more uniform permeability reduction along the cores length, but the magnitude of the permeability reduction was not as large (about 65%). The semi-continuous injection of oxygen-free medium resulted in a slower but a more uniform permeability reduction throughout the core compared to cores which received aerobically prepared medium. The selectivity of the process was investigated in a dual core system where two cores of 240 and 760 mdarcy permeability were connected parallel to each other without crossflow. Initially, about 85% of the total fluid flow passed through the high permeability core. After the addition ofBacillus species and medium, the flow pattern changed and about 85% of the total fluid passed through the low permeability core. These results show that the in situ growth of microorganisms can selectively plug high permeability zones and that control of the process may be achieved by alterations in the method of nutrient injection.

Effect of microbial growth on pore entrance size distribution in sandstone cores

SummaryThe in situ growth of microorganisms in Berea sandstone cores preferentially plugged the larger pore entrances. The largest pore entrance sizes after microbial plugging ranged from 20 to 38 μm, compared with 59 to 69 μm before plugging. The pore entrance size distribution of plugged cores was shifted to smaller sizes. A mathematical model based on Poiseuilles equation was found to adequately predict permeability reductions (greater than 90%) caused by microbial growth in the large pore entries.