Composite core laboratory displacement studies were undertaken jointly with the Petroleum Recovery Institute, Alberta, Canada to obtain key laboratory data needed to evaluate the applicability of this WAG mode oil recovery scheme in Dulang field. Composite core technology was chosen over conventional single coreflood test as the former provides larger pore volume for fluid contact and movement, reduces saturation end effects and allows assembly of cores from different sands.
Waterflooding was very successful in recovering 56.8% of the original oil in place. Oil water relative permeabilities were derived from the waterflood data and showed the core to be water-wet. Two cycles of gas and water flooding were carried out in rapid succession. In total, about 6.2% of the original oil in place were recovered additionally as a result of these floods. There is also an indication that some more oil may have been recovered from the core by vaporization into the gas stream. The composite core showed evidence of permeability loss and the pressure traces during the floods were quite noisy. This is probably due to the movement of fines and blockage/clearing of pore throats. Geological examination of the core material supports this observation since they were found to contain kaolinite and illite. These possibilities of altering the reservoir rock's flow properties need to be taken into account when designing field applications.