On the Principal Capabilities of Multi-probe Neutron Logging for the Calculation (Estimation) of Gas Reserves by a Volumetric Method in the Conditions of Gas Deposits in the North of the Tyumen Region
At the stage of development of gas fields, especially at a late stage, there are often problems associated with the difference between the reserves calculated by the volumetric method based on the results of geological exploration work and actually extracted - towards reducing them. One of the urgent tasks is to determine the current gas saturation of reservoirs in order to assess the uniformity of producing reserves by the volume of the deposit, to estimate the residual gas reserves in the watered productive sediments for the feasibility study of the expediency of their extraction. This problem became particularly topical in connection with the introduction, since January 1, 2016, of a new Classification of Reserves and Resources of Oil and Combustible Gases. The analysis of the application of existing methods of NGK and NOC on the basis of stationary neutron sources in the calculation of gas reserves is performed and their shortcomings are shown. The possibility of determining the gas saturation coefficient and the bulk gas saturation of the pore space of the collectors at different distances from the wall of the production column along the radial zones is shown on the basis of multi-probe neutron logging (MNC). The distribution of the geological parameters of gas saturation of the porous space of the Kg, Wr collector calculated on the basis of the MNK-Kr method by radial zones serves as the basis for the geological and geophysical interpretation and forecast of well productivity. The algorithm for calculating the geological reserves of gas deposits using a volumetric method involves volumetric gas saturation, which is determined by the MNK-Kr method, which is informative in conditions of cased and multicolumn well designs in the independence of the fluid that fills the well. The undoubted advantage of the MNK-Kr method is the ability to independently determine the three geological parameters characterizing the gas saturation of the reservoir: the porosity coefficient Kp, the gas saturation factor, and the bulk gas saturation. Clayiness of the reservoir does not affect the calculated values of gas saturation in conditions of low salinity of reservoir waters characteristic for gas deposits in the north of the Tyumen region. Diagnostics fluid dynamics of gas-saturated reservoirs by carrying out temporary measurements in the open trunk and after casing, cementing the casing allows to predict the reservoir’s reservoir properties.