Influence of relict oil saturation in a gas cap of oil-gas-condensate fields on the rate of hydrocarbon production

UDK: 622.276.1/.4.04
DOI: 10.24887/0028-2448-2020-1-50-54
Key words: relict oil saturation, hydrodynamic model, residual oil saturation, gas cap, critical oil saturation, end points, gas condensate loss
Authors: A.T. Zhubanov (Tyumen Petroleum Research Center LLC, RF, Tyumen), A.V. Tropin (Tyumen Petroleum Research Center LLC, RF, Tyumen), N.A. Cheremisin (Tyumen Petroleum Research Center LLC, RF, Tyumen)

It is known that in the pore space of many gas and gas condensate fields, along with residual water, relict residual oil is also contained. Relict oil is also found in the gas caps of oil and gas and oil and gas condensate fields. It is also believed that the oil reserves in gas caps are so small or not drainable that they are neglected during modeling. However, relict oil can significantly affect the hydrodynamic relationship between gas and oil saturated reservoirs. In the vicinity of the gas-oil contact, where oil was displaced by gas during the formation of the reservoir, the relict oil saturation should be close to the residual characteristic for this process with insignificant mutual dissolution. The presence of liquid and solid hydrocarbons in gas deposits sometimes reaches such volumes that the adjustment of the estimated parameters in the direction of reducing the useful capacity of the gas occupied becomes necessary. Relict oil is inherently motionless with any filtration mechanism. Residual oil saturation during the introduction of oil into the gas cap is formed from its capillary- blocked part and relict oil saturation. Accounting for relict oil saturation allows to improve the quality of the forecast, as well as to consider design decisions in the field of reservoir development, previously not taken into account. The article considers the influence of the initial (relict) oil saturation in gas caps on the rate of hydrocarbon production when using various methods for setting relict oil over a gas-oil contact. In addition, the necessity of dividing reservoirs into classes is discussed to justify the critical and residual values of oil and gas saturation, not only in terms of permeability and degree of hydrophilicity, but also in the nature of the initial saturation of reservoirs with hydrocarbons. On the example of one of the objects of the oil and gas condensate field shelf island Sakhalin, it is shown that assigning relict oil and revising the concept of the amount of residual oil saturation allows us to exclude a significant amount of losses of oil and gas products in the gas cap and to take a fresh look at the effectiveness of advanced gas development or joint development of a gas cap and rim.


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