The Effect of Bacteria on Sandstone Permeability

Abstract

Detailed descriptions are given of materials, apparatus and the experimental procedure used to study the effect of bacteria on sandstone permeability. The factors affecting permeability during injection of bacterial suspensions which have been investigated are:concentration of bacteria;core permeability and median pore size;species of bacteria, mode of aggregation and relative size;injection rate or pressure differential;mean pressure; anddepth of penetration of bacteria. The investigation demonstrated that bacteria cannot reduce core permeability to zero and that their effect on permeability is subject to definite limitations. Remedial or permeability restoration studies also were made. Acidization in combination with reverse flow was found to be an effective method for restoring permeability in cores partially plugged with bacteria. The relationship between the bacterial quantities in the laboratory tests and those found in field operations is discussed. The linear laboratory flow data have been translated into terms of field radial systems; these data indicate the most practical methods of maintaining injection rates in the presence of bacteria are to increase injection pressures or hydraulically fracture the formation. Introduction It has long been known that various bacteria flourish in the above-ground components of oil field water- injection systems. The presence of these bacteria has led to the suspicion that they might enter into the causes for reduction of injection well permeability, but only recently has an attempt been made to describe the effects quantitatively. Biocides are used in many cases without a firm knowledge as to whether the bacteria are killed, or if they are, whether the dead cells affect formation permeability. This project was undertaken as part of a study to determine the effect of bacteria, residual oil and precipitated solids such as iron sulfide or calcium carbonate on the permeability of sandstones and to learn whether any of these materials adversely affect brine injectivity in secondary recovery or disposal operations. This report deals with that portion relating to the effect of bacteria. MATERIALS CORES Three different permeability ranges of Berea sandstone cores were used in the study. The range of initial, absolute brine permeabilities ki were: high - 278 to 400 md; medium-130 to 162 md; and low-17.7 to 48.3 md. The permeability data for the cores used in the tests are included in Table 1. All cores were cut to a nominal 1 in. diameter. Following air permeability determinations, they were molded with an epoxy resin in 1.5 in. ID aluminum sleeves. The sleeves had drilled and tapped holes for intermediate pressure connections along the length of the cores. After molding, the high- and medium-permeability cores were trimmed to 4 in. in length and the low-permeability cores to 2 in. These lengths resulted in pore volumes of approximately 10.9, 10.4 and 4.4 ml. respectively, for the high-, medium- and low-permeability cores. Pressure transmitting channels were drilled through the plastic into the core proper, using the sleeve holes as drill guides. Width and depth of channel penetration into the core proper were approximately 0.03 in. and 0.05 in., respectively. Three pressure taps were used with all cores; for the high- and medium-permeability cores the taps were spaced 1 in. apart; for the low-permeability cores the taps were spaced 0.4, 0.8 and 1.2 in. from the inlet end. Pore size distributions were calculated from restored- state capillary pressure curves for representative cores in each of the three permeability ranges. In each case the pore size range with the greatest percentage of the pore space included the very small pores up to 0.5 micron in radius. The median pore radii were in the 5.5 to 6 micron range for the high-permeability cores; in the 4.5 to 5 micron range for the medium-permeability cores; and in the 3.5 to 4 micron range for the low-permeability cores. JPT P. 805^

Microbiological Methods for the Enhancement of Oil Recovery

“…In some cases pressure was measured at a serious of points along the core. There is general agreement that the injection of large volumes of dense bacterial suspensions produces a progressive reduction in permeability (Hart, Fekete and Flock, 1960;Kalish et al, 1964;Raleigh and Flock, 1965;Jenneman et al, (983). The most severe plugging occurs at, or close to, the injection face.…”

“…The greater the concentration of cells injected, the greater the degree of plugging. There is a concentration effect: a given number of cells causes more plugging if injected at low concentration than at high concentration (Hart et al~1960; Kalish et at., 1964). Kalish et at.…”

“…By contrast Hart, Fekete and Flock (1960) found that in some cases permeability was reduced almost to zero and were unable to relate permeability reductions to the initial permeability values of their rock samples. Using different bacterial species, Kalish et al (1964) concluded that large cells~ause more plugging than small cells and clumps cause more plugging than single cells. Jack, Thompson and DiBlasio (1983) isolated an anaerobic rod-.shaped isolate which grew as discrete cells on sucrose medium but as chains on glucose/fructose medium.…”

“…Microbiological enhancement of oil recovery 199 Kalish et al (1964) found that the adverse effects of bacteria on core permeability could be overcome readily by increasing the applied pressure, which increased permeability apparently by dislodging cell plugs, or by acid treatment followed by reverse flooding. Chlorine treatment is an alternative (Crawford, 1983).…”

The Effect of Bacteria Penetration on Chalk Permeability

“…Although previous investigations have revealed that bacteria can penetrate deeply into porous media (Jenneman et al, 1985;Kalish et al, 1964), a complete understanding of the penetration behavior of bacteria is lacking. Furthermore, there is limited amount of publications on microbial penetration/plugging study on chalk as earlier studies were conducted on sandstones (Jenneman et al, 1985;Kalish et al, 1964), micromodels (Afrapoli et al, 2011), glassbeads (Armstrong and Wildenschild, 2012) and sandpacks (Sarkar et al, 1994;Weiss et al, 1995). In all these porous media the pore sizes are considerably larger than in chalk rocks.…”