Tight Gas Reservoir Identification Method With Array Sonic Logging

The main gas formations in the western area of Sulige Field are He 8 and Shan 1 Member,which are composed of tight sandstone.Due to the tight formations,the contribution of the pore fluid to the well logging response is small.Hence,it is difficult to solely use the conventional electrical logging data to identify the oil and gas.As the velocities and amplitudes of the compressional wave,shear wave,and Stoneley wave are sensitive to the gas formations,the sonic logging data can be used to identify and evaluate the tight gas formations.Furthermore,abundant array sonic logging data are available in this area.Hence,in this work,we study the evaluation methods of the tight gas formations using the array sonic logging data for He 8 Member.This work enriches the evaluation methods of the tight gas formations in this area and improves the accuracy of the well logging evaluation of the natural gas reservoirs.First,the previous work on the interpretation of He 8 Member are reviewed and analysed.It is found that the tight gas formations have the following characteristics: 1)the porosity is small;2)the relation between porosity and permeability is complicated;3)the lithology is not stable;4)the electrical properties of the formations are not uniform and the controlling factor for the resistivity is not clear;5)the high resistivity formations often produce water.All these characteristics result in the poor identification of the fluid properties using the conventional electrical logging methods(the agreement rate is around 73%).In the Well E29 which fails to be evaluated by the conventional electrical logging methods,it can be found that the array sonic logging can identify the gas and water formations effectively.Hence,it is essential to carry out the study of using the array sonic logging data to evaluate the tight gas formations of Sulige Field.Then,a uniform interpretation platform for the array sonic logging data is developed based on Lead Software.This solves the problems usually encountered in the interpretation of the array sonic logging data,such as the complexity of the current interpretation software,the expensive and insufficient workstations,the lack of standardization of key parameters extraction from the slowness of the three waves,and the inconsistent interpretation platforms.The slowness of the three waves can be extracted accurately and quickly using the new platform,which provides the basis for using the array sonic logging data to identify the gas formations.Finally,five methods of identifying the gas formations are proposed based on the array sonic logging data,which include the identification through the comparison of the two compressional wave slowness,the differential effective Young's moduli,and the compressibility coefficient,etc.These methods are then tested in He 8 Member and the results show that the interpretation agreement rate increases by 5.2% compared to the conventional comprehensive interpretation.This work carries out the study on the identification methods of the tight gas formations based on the array sonic logging data,which enriches the methods of identifying gas formations and improves the agreement rate of the well logging interpretation of the natural gas formations.