川西地区须家河组三段勘探前景分析

AN ANALYSIS OF EXPLORATION PROSPECT OF THE THIRD MEMBER OF XUJIAHE FM IN WEST SICHUAN BASIN

一般认为川西地区须家河组三段是区域性烃源岩,同时又作为须二段储层的盖层,自身不具有勘探价值。从测井与地质结合的角度,对须三段储层的测井特征、钻井显示、盖层质量进行了初步分析。结果认为须三段具有良好的孔隙型含气储层,尤其是须三段中部具储集能力的砂体,距离烃源近而有可能先富集成藏,具有较广阔的天然气勘探前景。显裂缝不发育与钻井泥浆密度高是导致很多井在须三段显示不好的重要原因。分析指出累计砂岩厚度百分比大于50%的地区其须三段中部砂岩储层有可能获得天然气发现,须三段的评价可以从老井挖潜开始。近期的勘探实践证实了上述分析。

It is generally believed that the 3rd Member of Xujiahe Formation (T_3x_3) in West Sichuan Basin, a regional source rock acting as the cap rock of the reservoir in the 2nd Member of Xujiahe Formation (T_3x_2), is not worth exploration. The logging features, gas/oil shows in drilling and cap rock quality of T_3x_3 are preliminarily analyzed in this paper through combination of the logging data with geological information. It is believed that the third segment of Xujiahe formation (T_3x_3) of Triassic which is in the west area of Sichuan belongs to the territorial hydrocarbon resource. At the same time,used as the seal rock, T_3x_3 contains good gas-bearing reservoirs of porous type, and the reservoir sandbodies in the middle of T_3x_3 are close to source rock and would have become gas reservoirs first, thus they have relatively large gas exploration potential. Undeveloped fractures and high mud weight are the main causes of poor oil/gas shows in T_3x_3 in many wells. Gas discoveries probably can be obtained in the middle sandstone reservoirs of T_3x_3 in areas with a percentage of cumulative sandstone thickness over 50%. Appraisal of T_3x_3 can begin with potential tapping of old wells. Recent exploration practices confirm the correctness of the above analyses.