METHOD FOR ASSESSING THE IMPACT OF GEOLOGICAL HETEROGENEITY ON OIL SATURATION DISTRIBUTION

This article examines a method for assessing the impact of reservoir heterogeneity on the distribution of oil saturation in pay zones using the example of the Bajossian and Bathonian stages of the Jurassic system of the Kalamkas field. Within this field, the Jurassic oil and gas stratum under consideration lies on the eroded surface of various horizons of the Middle and Lower Triassic and is represented by uneven alternation of sand-siltstone and clay rocks, as a result of which these deposits have a complex geological structure, due in the lithological plan to uneven alternation of sand-siltstone and clay rocks. As a result, a rather complex distribution of oil (water) saturation may occur in the formation, which differs from the standard ideas about the geological structure of the object under study, i.e. the presence of such «unconventional» reservoir boundaries (oil-bearing contour) as capillary barriers of the first kind is possible. As a result of this approach, the following is obtained. For the conditions of occurrence of productive formations of the Bajossian stage of the field in question, in order to ensure that the dimensions of the capillary barrier in the reservoir do not exceed the height of 1 m at an average value of the porosity coefficient Kп = 27,6 % it is necessary to fulfill the inequality of Kпр ≥ 6,1∙10−3 μm2. For the conditions of occurrence of productive formations of the Bathonian stage, in order for the dimensions of the capillary barrier in the reservoir not to exceed the height of 1 m with an average value of the porosity coefficient Kп = 28,0 % it is necessary to Kпр ≥ 7,5∙10−3 μm2. Also, on the basis of this method, various ratios of Kпр permeability coefficients and porosity were obtained Kп at which the dimensions of the capillary barrier in the deposit will exceed the heights of 1.0, 1.5 and 2.0 m above the level of the accepted oil-water contact (OWC) for the conditions of occurrence of the Kalamkas field in question. It was noted that this approach makes it possible to assess uncertainties in the position of fluid contacts when justifying the boundaries of the oil potential contour and the distribution of oil reserves in formations with a wide range of reservoir properties.