The exact determination of water saturation is one of the most important and complex questions for estimation of hydrocarbon reserves. The laboratory test quality influences on the successful solution of this problem. However, at the present there is no single standard for the case of low-permeability reservoirs. The analysis has revealed that the OST 39-204-86 (industrial standard) provisions that were developed in 1986 for good reservoir properties and low clay content in the pore space, not for low-permeability reservoirs. In this paper the experimental protocol for core test using semipermeable membrane is considered. The advantages and disadvantages of this method are pointed out. Recommendations for increasing the informativity were developed. It includes: the sampling from different lithological groups, the scheme for capillary pressure changing for laboratory test in the case of low-permeability rocks (at least 11 steps with a maximum pressure value not less than 1 MPa), an algorithm for the transition between pressure steps (at least 72 hours needed after filtration ceased), individual capillarimeter test necessity (at the atmospheric and reservoir conditions). In addition, the criterion for the capillary pressure curves quality was developed. The most common reasons of poor quality results are considered. The additional useful information from experimental investigations (pore size distribution, wettability parameter, etc.) is discussed.
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