Abstract:

The developed faults,lost and repeated formations and diversified lithology are the features of Sanlutian bore field, therefore, it is difficult to identify the lithology. As a result,log data are used specifically to study the formation lithology of Sanlutian bore field. By analyzing the log response characteristics for different lithological in fourteen gas hydrate drillings, Gamma ray log, neutron log and density log are optimized as the sensitive parameters to lithology identification. The lithological identification plate is made by cross plot technique and the identification criterion is built, which are used to identify and subdivide the lithology in Sanlutian bore field. Seven kinds of lithology can be identified by the log data, including sandstone, siltstone, argillaceous siltstone, silty mudstone, mudstone, oil shale and coal. According to the lithology identification result, the horizontal distribution of lithology in Sanlutian bore field is that sandstone in the east has good physical property and the well -developed mudstone is in the west; vertical distribution is that the sand to shale ratio is 4.48 in Muli Formation which has coal beds of 204.5 meters, while 0.84 in Jiangcang Formation that has abundant mudstone and oil shale which means better for the hydrate occurrence.The logging identification results of lithology lay the foundation of locating the favorable reservoir of gas hydrate in Sanlutian bore field.

Key words: lithology identification, gas hydrate, well log, Sanlutian bore field