The authors carried out laboratory study to assess the optimal composition of injection gas to achieve oil and gas miscibility under the conditions of one of the oil-gas-condensate fields in Eastern Siberia. The oil of this field is light, of low-viscosity, sweet and low-resinousness. Initial stage of reservoir development is considered.
We carried out physical simulation of oil displacement by four type of gas. Slime-tube reservoir model saturated by recombine oil. Gases models were prepared as mixture of individual components of hydrocarbon gas and associated wet gas (propane-butane fraction). Gases models had 10% differences by sum of C3+ components.
As far as formation oil volume factor changes during gas dissolution in oil standard volumetric method gives seems to be inaccurate for oil displacement coefficient estimation. That is why we developed a method for oil displacement coefficient estimation by mass irrespective of formation oil volume factor. Tests results showed that differences in oil displacement coefficient assess can achieve 0.03.
We fixed several gas displacement drives. Displacement conditions changed from partially-miscible to miscible according to wet gas content. Beginning with gas composition No.2 multiple contact process started. Formed multiple contact fluid represented hydrocarbon mixture of modified composition; it differed from original oil by colour. Further increase in content of wet components (to 30%) in injection gas was not result in noticeable growth in oil displacement factor.
Gas composition No.3 (content of С3+ components is 20.5%) was optimal for minimum miscibility enrichment under conditions of regarded oil reservoir. Increase in wet components to 30% resulted in all injection gas spend to oil enrichment and exclusion of gas intrusion. Research was carried out to the accuracy 1-2% using specially designed and tested methods. The results may be applied for mathematical model matching.
References
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