SUN Chun-yan, WANG Hong-yu, NIU Bin-hua
China University of Geosciences, Beijing 100083, China

　　In this paper, studies of method and applicability are emphasis. With oil and gas geological data、seismic exploration data and geochemical prospecting data, integrated interpretation and evaluation research on Xisha trough for the investigation of gas hydrates are systematical developed. Methods are also summarized.
　　In the gas hydrates interpretation research on Xisha ocean trough, several results are obtained:
　　(1) Through geomorphologic, depositional and tectonic conditions analysis, the study area displayed a favorable gas hydrates investigation prospect. (2) Through structural interpretation, tectonic features of the research area, relations between BSR and local structure and structural effects on gas hydrates formation are made clear. (3) Through seismic attributes analysis, bottom simulating reflector, blanking reflector and velocity-amplitude features distribution regions are pointed out, and bright spots, reversal of poles, abnormal instantaneous frequency and anomalous AVO attributes seismic reflection phenomena as well as their relations are indicated. (4) By geochemistry testing, we found high gaseous hydrocarbon content regions and summarized rules of vertical change of hydrocarbon content and their contacts with depositional environment. (5) The comprehensive identification of methane carbon isotope and hydrocarbon gas humidity shows that the most gaseous hydrocarbon in the submarine sediment in this study region is pyrogenetic with a little part of biogenetic in addition. Combined with the geology analysis, we determined that the methane of gas hydrates which may exist in the sedimentary formation should be pyrogenetic. (6) The methane gas and gas hydrates model of study area should be named fault-percolation aggregative model. There are several gas migration power sources. The fluid courses are not only faults, but also caused by strata percolation. That is why non-identity occurs between areas of BSR and the high methane content in sediments. (7) Finally, through comprehensive analysis on each aspect, several favorable marine gas hydrates exploration regions are pointed out in this paper.
　　We also found some rules in the geochemistry research aimed at the gas hydrates prospecting. (1) In the depth from one meter to four meter below the seafloor, deposition sample contain abundant information and have highly differentiated geochemical characteristics. The deep samples are more fit for geochemical parameters analysis. (2) Measurement by head space gas sensor is simple and convenient, and is more fit to test hydrocarbon in field. Acidolysis hydrocarbon chromatography method is adaptable to in-house procedure. (3) It’s an effective method to discriminate gaseous hydrocarbon genesis of submarine sediment through comprehensive identification of methane carbon isotope and hydrocarbon gas humidity. And in some means, gaseous hydrocarbon genesis of sediment can indicate gas hydrates genesis that below these sediment. (4) Comprehensive analysis on geologic、 geophysical and geochemical parameters is able to clarity gas hydrates genetic model and definite favorable exploration target, and can directly point out the future exploration direction. (5) Aiming at geochemical prospecting for gas hydrates investigation, the author has designed a data processing procedure and a method of quadrant distance reciprocal weighed geology data interpolation. (6) We conclude that we should introduce more technologies of geologic evaluation and management process in oil and gas exploration, make a systematic study aimed at the importance and effectiveness of every interpretation and evaluation method, and accomplish a perfect combined technology system for gas hydrates prospecting study.