Page 174 - Primer on Enhanced Oil Recovery

164 Primer on Enhanced Oil Recovery

on: oil density, viscosity and volume expansion are modified, surface tension on
oil/water interface are altered. All this usually positively affects phase permeability
through formation. Rather negative effect can be observed in clay swelling.
The microbial surfactants reduce the interfacial surface tension at water/oil
boundary and at the rock surface. This allows for globules of residual oil, retained
in the porous medium by capillary forces, to become mobile. Microbial surfactants
have a high emulsifying ability and form highly dispersed oil-in-water emulsions,
which helps to achieve uniformity in the displacement front. The biopolymers
formed as a result of the vital activity of microorganisms alter the rheological prop-
erties of reservoir fluids and help to reduce fingering in the displacement front.
The above processes in their synergy have a significant impact on the final oil
recovery. It is obvious that the microorganisms mechanism of enhanced oil recov-
ery has the same base as in other EOR techniques. However, it is difficult to isolate
the dominant oil displacement mechanism in this case. All of the above processes
take place simultaneously. It is obvious and highly probable that the high efficiency
of biotechnology is not a function of any one single factor, as is the case when
using physicochemical methods of reservoir stimulation. The effect of MEOR is
determined by the integral synergistic effect of many processes.
One or another process or mechanism at each individual physical (formation)
site or even strata may play a greater or lesser role in the oil displacement process.
One can try to map bio-products and bio processes to the basic reservoir stimulation
techniques as it is shown at Fig. 13.2. Realization of prevailing impact mechanism
nevertheless depends on the formation geological conditions.
Experimental studies on flat horizontal reservoir models revealed that microbio-
logical exposure contributes to an increase in the oil displacement ratio by 15 20%
compared with ordinary water.
When using the microbiological method of enhanced oil recovery, based on the
functional activity of hydrocarbon-oxidizing microorganisms in the fields producing
paraffinic oil, it is possible not only to significantly increase the oil recovery in the

Figure 13.2 Relation between microbial EOR products and basic reservoir stimulation
processes.