Abstract

A novel process for sand consolidation and sand production control has been developed. The procedure involves the use of bacteria that actively precipitate calcium carbonate as a cementing agent. A series of experiments was performed in the laboratory and showed that loose unconsolidated sand is transformed into a well cemented sand. Porosity was reduced by up to 50% and permeability was reduced by up to 90% in the areas where cementation took place. Facial plugging was avoided. Computer Assisted Tomography was used for the visualization of the cemented areas and the determination of the porosity distribution before and after the consolidation process.

RECENT TRENDS IN MEOR

Microbial Enhanced Oil Recovery (MEOR) is still considered an emerging technology, but it is certainly not new. Both micro-organisms and microbially derived products have been used for over 40 years to recover reservoir oil or provide wellbore cleanout (Nelson and Launt, 1991). Microbes are blamed fDr prDblems related to the creation of biofilm that plugs reservoir pores, the creation of ferrous sulfide which is often responsible for plugged and fouled production lines and degradation of chemicals used in EOR processes. However, micro-organisms have also been credited for a wide range of metabolic by-products that are helpful to oil recovery Also some anaerobic micro-organisms produce hydrocarbon gases and some aerobic Organisms produce CO2 gas.

A variety of MEOR approaches have been used including:

  • Slimulation of the indigenous (existing) microbial populations,

  • Injection of nutrients, biocatalysts, and selected micro-Organisms with a proven ability to perform in situ,

  • The above ground production of microbial products, such as biosurlactants, biopolymers, fermentation alcohols and kelones which are injected like tradisional EOR chemicals (Jack, 1990; Nelson and Launt1991).

Early work in MEOR has been summarized in Proceedings of MEOR workshops (King and Stevens, 1987). The National Institute for Petroleum Research (NIPER) has spent considerable effort in MEOR, addressing in situ microbial growth and metabolism, effective plugging by microorganisms, polymer producing bacteria and biosurfactants (Mcinerney et al., 1983: Knapp et al., 1987).

The effects of the presence of bacteria on the permeability of Berea sandstone were investigated by Kalish et al. (1964). They injected dead bacteria under a variety of conditions and found that the factors which affect permeability during injection of bacterial suspensions are:

  1. concentration of bacteria,

  2. core permeability and median pore size,

  3. species of bacteria, mode of aggregation and relative size,

  4. injection rate or pressure differential,

  5. mean pressure and

  6. depth of penetration of bacteria.

Core permeability was never reduced to zero. Permeability restoration was achieved by acidization in combination with reverse flow.

Nutrients such as glucose, ammonia, nitrogen and phosphate can be transported through sandstone in concentrations sufficient to support microbial growth and metabolism for EOR processes (Jenneman et a/. 1984). Viable cells have been transported through sandstone with a permeability as low as 196 mD. Less than 1% of the injected cells were recovered in the effluent.

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