A Study of Formation Plugging With Bacteria

Abstract

This study investigated the nature of formation plugging with bacteria and attempted to relate its characteristics to physical rock properties. Fifteen core samples of four specific formation types were defined and plugged using a commonly occurring, uniform sized dead bacteria, Bacillus subtilis. Two of the formation types were fairly uniform-grained sandstones and two were heterogeneous carbonates. The injection rate and concentration of solids in the brine were held constant during the test runs. The pore geometry factor G was a significant petro-physical rock characteristic for correlation with depth of plugging, but lacked importance as a parameter for rate of plugging. Although the G factor may not completely describe porous rock geometry for plugging predictions, for reservoirs with multi-pore systems, there is evidence that the pore geometry factor might form a basis for establishing injection water specification in more homogeneous reservoirs with only primary porosity development. Introduction GENERAL PURPOSE Injecting water into oil-bearing formations to increase recovery is common practice in the petroleum industry. One of the most serious operational problems involved with water injection wells is the tendency of the porous rock immediately adjacent to the injection wellbore to plug partially. This results in increased injection pressures and/or a decrease in the rate of injection. This plugging in injection wells can result from a number of causes, including bacteria contained in the injected water. The purpose of this work was to investigate the nature of injection plugging with bacteria and to attempt to relate its characteristics to physical rock properties. Many variables exist in research of this type, so, to reduce them, injection rate and concentration of bacteria in brine were held constant. The bacteria used for plugging was a uniform-sized, dead bacteria, Bacillus subtilis, a micro-organism commonly found in water, air and soils. Four specific porous rock types were plugged-two consolidated sandstones and two heterogeneous carbonates. The experimental work involved two distinct phases. The first concerned determining the physical rock properties and the second was the experimental work of actually plugging the selected core samples. PORE GEOMETRY FACTOR Capillary pressure is necessary to displace a wetting fluid from a capillary opening with a nonwetting fluid. The factors which govern capillary pressure are the surface or interfacial tension of the fluids involved, the system wettability and the equivalent pore radius. Thus: (1) Thomeer used the idea that the location and shape of the capillary pressure curve reflect characteristics of the pore structure of any porous media sample. He presented the mathematical description of capillary pressure curves and of indicated differences in pore geometry of samples. (2) where G = pore geometry factorpc = capillary pressurepd = displacement pressure(Vb)pc = fractional bulk volume occupied by thedisplacing fluid at any capillary pressure(Vb)px = fractional bulk volume occupied by thedisplacing fluid at infinite pressure ortotal inter-connected pore volumes. The shape of the curve is defined by the pore geometry factor G. The curve shape is related directly to the sorting and interconnection of the pores of the sample. The location of an infinite number of curves can be defined by the same asymptotes. However, these curves differ in shape, each curve being described by a specific value of G. Thus, the description of a curve is unique when, in addition to the position of its asymptotes, its shape is defined. These curves can be used graphically to determine the characteristic parameters of any arbitrarily located curve. Those parameters that can be approximated from any capillary pressure curve are:total interconnected pore volume, represented by (Vb)px;extrapolated displacement pressure, the abscissa axis; andpore geometry factor, by the curve shape. PROPERTIES OF BRINE AND BACTERIA The fluid used throughout this study was an aqueous solution of sodium chloride, 25,000 ppm by weight. The addition of salt to fresh water was intended to eliminate clay swelling in the sandstone cores and to retard leaching in the limestone cores. JPT P. 201ˆ

Investigation of spore forming bacterial flooding for enhanced oil recovery in a North Sea chalk Reservoir

“…The pressure increase during bacterial injection into all the five different cores indicates that bacteria accumulate and plug the porous medium near the injection point. This result is expected and is similar to observations by other investigators for the different porous media (Raiders et al, 1986;Raleigh and Flock, 1965;Shaw et al, 1985). The pressure data clearly show that effective permeability decreases more significantly in the presence of bacteria in heterogeneous cores.…”

“…Even though studies of microbial plugging have been conducted by many researchers, to the best of our knowledge none has been performed on chalk. Earlier studies have been conducted in packed glass beads (Shaw et al, 1985), sandstones (Crescente et al, 2005;Cusack et al, 1992;Raiders et al, 1986Raiders et al, , 1989Raleigh and Flock, 1965;Yakimov et al, 1997), sandpacks (Cusack et al, 1992;Suthar et al, 2009), outcrop limestones (Al-Hattali et al, 2013;Kaster et al, 2012;Raleigh and Flock, 1965) and outcrop carbonates Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/petrol (Salehizadeh and Mohammadizad, 2009;Biria et al, 2013).…”

“…After the system was injected with Bacillus strain 47 and nutrient, the flow pattern changed and about 90% of the total injected fluid was diverted to the low permeability core. Raleigh and Flock (1965), conducted core flooding using four distinct core types: Berea sandstone (homogeneous type), Cardium sandstone (less uniform sand grains compared to Berea, but a clean, well-sorted rock type), Devonian rock (a completely heterogeneous type), Indian limestone (outcrop rock, composed of oolitic porosity with secondary, small, vuggy and pinpoint porosity). Bacillus subtilis was used and it was observed that the majority of plugging observed in clean, homogeneous, uniformly grained, consolidated sandstone was located near the inlet face of a core.…”

Starvation and penetration of bacteria in soils and rocks

“…The rates were reported to be independent of permeability where the rocks were above 100 millidarcys, however below this permeability penetration was limited. Some of the early studies on the transport of bacteria injected dead bacteria into rocks 23,59. In such instances bacteria were treated as inert particles and have been reported to cause a jamming effect at the inlet of rock cores when injected at high concentrations 23.…”

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.…”