Study On Logging Response Mechanism Of Natural Gas Hydrate Reservoir In Qilian Mountain

Geophysical logging is an important means of gas hydrate exploration.First of all,the formation of gas hydrate needs proper temperature and pressure conditions,the gas hydrate will decompose when it is removed from the required environment,and the geophysical logging method can measure the characteristics of formation in the temperature and pressure environment of the original formation,therefore,the geophysical logging method is an irreplaceable method in the discovery and research of natural gas hydrate.Secondly,the gas hydrate reservoir has a good display on the well logging curve and has relatively obvious logging response characteristics,which is an effective way to explore and find gas hydrates.In addition,the geophysical logging method has the characteristics of continuity,which can obtain continuous and more reliable observation data through logging coring.So far,geophysical logging method has been paid more and more attention in the exploration of gas hydrate drilling,and has the extremely widespread application.The identification and the use of logging data of natural gas hydrate(NGH)play an important role in reservoir evaluation.This paper is based on one of the sub-projects of the project of "natural gas hydrate exploration in the frozen soil area of qilian mountain",which is undertaken by the oil and gas resources investigation center of China geological survey,and the study area is Sanlutian well field in qilian mountain.On logging data correction and validity analysis,summarizes the research area of logging response characteristics of hydrate reservoir,and based on the core rock physics experiment results,combining with the logging curve,studying acoustic and resistivity logging response mechanism.By analyzing the data of rock physical experiment we get the results: 1.as the temperature decreases,the resistivity of the rock increases faster;2.The rate of increase of core resistivity is higher than that resistivity of formation water;3.The resistivity of core in low temperature environment is about twice that of rock resistivity under room temperature.The resistivity logging in the study area is significantly increased in the hydrate layer,and the non-hydrate layer is low;the interval transit time logging data is low in the hydrate layer,and the response value of the non-hydrate layer is higher,and it is accompanied by the cycle-skip.The porosity and hydrate are the main affecting factors of the acoustic velocity logging value in the study area.In the sandstone formation,the resistivity logging value is mainly influenced by porosity,mud content and hydrate.In the shale layer,resistivity log values are mainly affected by fractures and hydrates.According to the response mechanism of acoustic velocity and resistivity,respectively set up acoustic velocity factor and resistivity factor identification method which can identify the hydrate in the study area,by comparing the identification results,the identification method of the resistivity indicator is better in the research area,and it is suggested to be used in the research area.