METHOD FOR ESTIMATING GAS REMAINING IN A PLATE IN THE FORM OF FREE GAS SATURATION ZONES

As it is known, when developing an oil reservoir in the dissolved gas mode, not all of the gas released from the oil comes to the surface, part of it remains in the reservoir in the form of free gas saturation zones. Not accounting for this gas can lead to a distortion of the actual situation that has developed in the reservoir and the inefficiency of subsequent measures taken to develop it. In this regard, questions arise about how to determine the presence of gas remaining in the reservoir and how to assess its amount. This article is devoted to solving the questions posed. An example is the Hassi-Mesaud field, located in Northern Africa. During the operation of the field, a weak activity of circulating water and a rapid drop in reservoir pressure were noted, which led to intensive expansion of the gas cap and the release of dissolved gas from oil. The considered field is characterized by a sharp heterogeneity and an extremely unfavorable ratio of phase permeabilities of gas and oil. If in ordinary fields the equality of oil and gas production rates in reservoir conditions is achieved at a gas saturation of 7 - 17 %, then in the field under consideration this condition is achieved at a gas saturation of 2.5 %. The task of determining the presence of free gas saturation zones was reduced to constructing a graph of the relationship between the ratio of the phase permeabilities of oil and gas and gas saturation. Such dependence was built for data obtained on the basis of core studies and field studies. The analysis of the constructed curves made it possible not only to determine the presence or absence of gas in the reservoir, but also to make an approximate assessment of the share of this gas in the total volume of the total gas released from oil.