Summary
The wettability relationships between oil, brine, gas, and rock are
important in understanding reservoir dynamics. Chemical surfactants, scale
inhibitors and microbes introduced during exploration and production are all
known to affect reservoir wettabilty. However, little thought has been given to
the possibility of microbial contamination of cores during core preservation,
handling, storage, or analysis and the effect that this may have on measuring
parameters such as wettability. In an attempt to understand how wettability
analysis of sandstone cores may be altered by the presence of microbial
contamination, this paper examines the effect on wettability of
bacterial/fungal biofilms on quartz. Wettability data for quartz and quartz
colonized by bacterial/fungal biofilms were collected using an environmental
scanning electron microscope (ESEM). The results illustrate that the
introduction of bacteria and fungi to such systems can change wettability from
hydrophilic to hydrophobic. These findings have important implications within
the oil industry.
Introduction
Core Analysis and Biological Contamination. During core analysis
studies of reservoir rocks, many parameters are recorded, such as porosity,
permeability, mineralogy, and wettability (Anderson 1986a, 1986b). Wettability
has important implications for factors such as relative water and oil
permeabilities, resistivity, and capillary pressure (Anderson 1986a, 1986b,
1987; Wang et al. 1997).
The development of microbiological growths within porous reservoir rock,
such as sandstone, has many important implications for parameters such as
porosity and permeability, for example by pore blocking (Udegbunan et al. 1991;
Hayatdavoudi and Ghalambor 1996; Lappan and Fogler 1996; Brydie et al. 2001).
New mineral phases may be biologically mediated and precipitated (Adams et al.
1992; Feldmann et al. 1997; Konhauser and Urrutia 1999; Neumeier 1999; Adamo
and Violante 2000), and certain mineral phases may be particularly susceptible
to chemical and physical alteration or destruction through biological action
(Weed et al. 1969; Barker and Banfield 1996; Bennet et al. 1996; Paris et al.
1996; Ullman et al. 1996; Barker et al. 1998; Wakefield and Jones 1998; Welch
and Ullman 1999). In addition, the coating of mineral grains by the growth of
bacteria and fungi may potentially alter the overall wettability of the core
sample. This paper's focus is on this potential for alteration of wettability
brought about by the presence of such microorganisms.
Biological contamination of core materials can occur at many points during a
core's history, during core handling, preservation, or even while performing
laboratory tests. It is also possible that microorganisms are present from the
reservoir. Given those problems, it is of importance to minimize the degree of
biofilm formation.
For the purpose of this paper, a biofilm is defined as "a population of
microorganisms concentrated at a solid/liquid interface." No inference is made
as to the thickness of the film, although, in the present study, biofilms were
typically found to be 1 or 2 cells thick. The biofilm also includes extra
cellular products, such as proteins, that may be released by the microorganisms
and coat surfaces.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
27 November 2007
- Revised manuscript received:
18 June 2009
- Manuscript approved:
19 June 2009
- Published online:
5 November 2009
- Version of record:
12 March 2010
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