Page 427 - Fundamentals of Enhanced Oil and Gas Recovery

Microbial Enhanced Oil Recovery: Microbiology and Fundamentals 415

porous media and consequently increase the oil recovery. At the end of the incubation
period, the well is backed to production and oil along with the produced biochem-
icals will be produced. The injection rate and also the kinetics of the microbial process
will determine the area to be affected by bacteria [407]. This process might be
repeated several times to maximize the oil recovery, hence, this process has been
referred as microbial huff and puff too [411].
McInenery et al. [412] categorized the cyclic oil recovery in two main categories of
(1) well stimulation and (2) fermentative microbially enhanced waterflooding processes.
The difference is that in the latter, the injected nutrients (and microorganisms in cases
the indigenous microorganisms are not present) are injected deep into the reservoir
rather than to the well vicinity. Well stimulation approach was used in several early field
trials due its simplicity [78,413,414]. Hitzman [78] specified this approach has been the

most effective in carbonate well with a temperature range of 35 40 C, oil gravity of
3
875 965 kg/m , and salinities less than 100 g/L. It should be noted there have been
inconsistencies in results acquired from several field trials and also little changes in the
oil production from sandstone reservoirs has been observed [78,87] (Fig. 10.5).

10.9 MEOR METHODS

There are three general MEOR applying approaches, which are debated in the
following.

Injection Incubation (shut-in phase) Production
hours days to weeks weeks to months
Microorganisms
and nutrients

Produced oil
and products

Oil Oil Oil
in in in Depleted
place place place oil sand

Injected microorganisms Metabolic activity produces Oil and
and nutrients CO 2 and surfactants products

Figure 10.5 Schematic representation of cyclic microbial recovery. Courtesy of the National Energy
Technology Laboratory and the U.S. Department of Energy.