Residual Hydrocarbon Saturation in the Transition Zone and the Gas Cap

The laboratory study of the formation of residual oil saturation in a gas cap after active gas production from it and the penetration of oil from the underlying oil reservoir is currently not regulated in any way. Residual oil saturation in the gas cap was taken and is accepted, as a rule, from the correlation dependences with reservoir properties obtained from experiments on oil displacement from to the limit oil-saturated core samples. The use of similar correlations for the transition zone significantly underestimates the mobile oil reserves in such zones In this connection, the paper discusses the technology of physical modeling of the residual oil saturation in the gas cap after the penetration of oil into it and the issues related to the determination of the residual oil saturation in the transition zones of oil reservoirs. On a series of test experiments on core samples of a weakly consolidated reservoir of the Pokurovskaya formation carried out according to the method developed by the authors, it was shown that the values of residual oil saturation after the penetration of oil into the gas cap are significantly lower than for oil-saturated formations with similar properties. It is shown that such studies will make it possible to clarify the possible irreversible oil losses during the advanced development of gas caps and to revise the approaches to the development of oil reservoirs of gas-oil and oil-gas fields. Laboratory modeling and study of the process of oil penetration into a gas cap and its subsequent displacement by water or gas is relevant for almost 10% of Rosneft's current reserves.