Abstract:

In Sanlutian well field, the drilling results reveal that gas hydrate mainly occurs in the fractured and porous reservoirs. Based on the results of drilling and log lithology identification, by using conventional and ultrasonic imaging log data, this article summarizes the log response characteristics of the both kinds of reservoirs respectively, and establishes identification methods which use log data to divide gas hydrate reservoirs in this area. The results show that:(1)compared to shale section，the fracture is developed, and sonic velocity is relatively high(in the range of 1.5 to 4.5 km/s) and the resistivity is up to 90 Ω·m in fractured gas hydrate reservoirs; compared to the aqueous layer of sandstone, the acoustic velocity is of relatively high value in the range of 2.0-4.0 km/s, the resistivity is also of relatively high value in the range of 90-180 Ω·m in porous hydrate reservoirs. (2)12 layers of fractured reservoirs and 15 layers of porous reservoirs which have a total thickness of 217.2 m are identified in the 14 wells of the study area. All the thick drilling reservoirs can be identified except a small amount of thin ones，and the most possible reason is that log response is unobvious to less content of gas hydrate. Overall, the application effect of log methods is good at the identification of gas hydrate reservoirs in the Sanlutian well field.

Key words: Sanlutian well field, permafrost region, gas hydrate, log response, reservoir identification