Laboratory displacement tests using alkaline steamflood and conventional steamflood were successfully conducted. The results from the experiments were used to obtain correlation equations which in turn were used to simulate oil recovery performances.
A chemical displacement model which incorporates the thermal and chemical oil recovery mechanisms was used to history match the experimental oil recovery performances. The model prediction of the oil recovery performances matches fairly well with the experimental results. Furthermore, the model was tested with data obtained from the displacement tests and it led to some modification and adjustment until its application for history matching and prediction became satisfactory.
The model predicts higher oil recovery for caustic steamflooding over conventional steamflooding and agrees quite well with the experimental results obtained. The experimental results show that caustic steamflooding recovers more oil with increase in temperature, but above 300 F the incremental oil recovery becomes insignificant. The optimum temperature for enhanced oil recovery by caustic steamflood seems to be about 300F. At a given temperature caustic steamflooding recovers more oil than conventional steamflood by between 18 to 35% and 8 to 13% of the original oil in place for primary and secondary recovery processes place for primary and secondary recovery processes respectively.
Eighty percent of oil produced by EOR projects in the United States results from steamflooding. Steam appears to be the most efficient hot injection fluid because of its large gross heat capacity. However, steam has the tendency to override the lower portion of the formation due to gravity segregation. Thus, chemical additives are suggested for improving the volumetric sweep efficiency of steam by mechanisms similar to chemical flooding.
The primary function of chemical additives in enhanced oil recovery is to alter the mobility characteristics of the fluid phases by reducing the interfacial tension between oil and water, which results in the increase of the relative permeability to the oil. Therefore, chemical permeability to the oil. Therefore, chemical additives can improve the sweep and displacement efficiencies of steamflooding, but screening tests must be performed to select the most effective additive for individual applications.
Sodium hydroxide is an inexpensive material and its reaction with acidic crude forms surfactants that can withstand high temperature and pressure. Hence, the addition of sodium hydroxide or other alkaline solution to steam during steamflooding seems to be a promising technique for enhancing oil recovery. The successful addition of caustic solution to steam requires that its PH does not fall below an effective level.
The alkaline steamflooding technique can be applicable to a water flooded reservoir when the oil's acid number is greater than 0.5. Fairly clean reservoirs are the best candidates because alkaline solution consumptions will be high with increasing amount of clay and carbonates. Scale formation and formation damage can occur in reservoir with high gypsum and clay content. However, dissolution of silica in alkaline environment is known to have caused scales formation in producing wells. Okoye et al and Delghani and Handy concluded that the dissolution reaction rate of silica increases with increasing temperature.