Study On Methods Of Log Interpretation Of Gas Hydrate Reservoirs In Sanlutian Well Field, Qinghai Province

As a potential alternative energy with huge reserves, gas hydrate has been concerned greatly nowadays. Qilian Mountain permafrost region is the first place of the world in which gas hydrate is found in mid-latitude mountain permafrost region, the exploration and development of it have become a hot issue. Thanks to its physical properties and influence on physical properties of the reservoir rock, the abnormal log response of resistivity, sonic velocity, density and other geophysical log measurements is an effective identification of gas hydrate reservoirs. The resources of gas hydrate mainly depends on the distribution, thickness, porosity of reservoirs, and saturation of gas hydrate, and these physical parameters are related on the conventional log parameters of formation, so there is a great significance for the exploration and development of gas hydrate to research the log response characteristics of gas hydrate reservoirs.Based on the results of drilling and log lithological identification, this article uses the data of conventional log and ultrasound imaging log of some gas hydrate wells, summarizes the different log response characteristics of the fractured and porous gas hydrate reservoirs in the Sunlutian well field, Qinghai Province, and compares the typical log response characteristics of gas hydrate reservoirs in domestic and foreign area. It presents two log identification methods of two types of gas hydrate reservoirs in the study area, and summarizes the various existing methods of reservoir parameters calculation in domestic and foreign area. Then it analyzes the application effects of the methods of reservoir identification and parameter calculation in the study area.The result shows that:(1)compared to shale section,the fracture is more developed,sonic velocity is higher(in the range of 1.5~4.5km/s)and the resistivity is up to 90Ω·m in fractured hydrate reservoirs, and compared to the aqueous layer of sandstone, the acoustic velocity is of higher value in the range of 2.0~4.0km/s, the resistivity is also of higher value in the range of 90~180Ω·m in porous hydrate reservoirs.(2)Determining each log identification methods of the two hydrate reservoirs, namely, using the data of conventional log and ultrasound imaging log to identify fractured gas hydrate reservoirs, and using intersection of log data of resistivity and sonic velocity to identify porous gas hydrate reservoirs. The identification results show that the application effects of these methods are good.(3)Based on core data, the effects of using density and gamma ray log data to regress the porosity and using simplified Archie formula to estimate the saturation of gas hydrate are the best among all the log evaluation methods.