渤海湾盆地渤中凹陷深埋古潜山天然气成藏主控因素探讨

Major controls on natural gas accumulations in deep-buried hills in Bozhong Depression,Bohai Bay Basin

渤中凹陷钻探的两口科学探索井均在古生界潜山发现天然气流,其中科A2井经测试获日产天然气40.2×10~4m^3,揭示了渤海海域目前埋深最大、温度最高的古潜山天然气藏。根据渤中凹陷渤中21~22古潜山油气成藏条件和实际地质、测井和地震资料的综合解释,对研究区天然气成藏控制要素进行研究。结果表明:古潜山圈闭面积大,且具有完整背斜形态;深层沙四段—东三段发育大量优质高成熟烃源岩,油气源充足;古潜山储集空间为溶蚀孔洞和裂缝,储层物性较好;成藏要素匹配关系好,天然气具有明显的晚期持续充注成藏的特点。该古潜山气藏的发现,不仅是渤中凹陷深埋古潜山天然气勘探的重大突破,也是深埋古潜山油气成藏地质条件认识和勘探工程技术进步的重大成果,能够推动渤海海域乃至整个渤海湾盆地凹中深埋古潜山的油气勘探工作。

Paleozoic commercial gas reservoirs were discovered in deeply buried hills in Bozhong depression by two scientific exploration drilling-wells.The gas production from the A2 well was up to 40.2×10^4m^3,and the gas reservoirs were currently the deepest buried and have the highest subsurface temperature in the offshore Bohai Bay Basin.Gas accumulations in the buried-hill reservoirs and their controls were studied by systematic interpretations on core data,well-logging data and seismic data in Bohai sea,and the results suggest that there are four major contributors for the gas accumulation in Bozhong 21-22 buried-hill reservoirs：Bozhong 21-22 buried-hill reservoirs were large anticlines with enough trapping areas for the gas;there were good source rocks of members Sha-4 to Dong-3 in the Bozhong Depression with huge thickness,which were in high hydrocarbon potentials and thermal maturity;great reservoir spaces with dissolved caves and fractures were developed in the buried-hills with good petrophysical properties;and the gas were accumulated obviously late and were in good timing among essential elements of petroleum geology,which meant late and continuous gas charging into the buried-hills so significant controlling on hydrocarbon accumulation.The successful discovery of Bozhong 21-22 buried-hill gas reservoir is not only a breakthrough of natural gas exploration for buried-hills in deep part of the depression,but also an achievement of understanding hydrocarbon accumulation in buried-hill reservoirs in the deep part of the depression,which provides a great prospective to oil and gas exploration in buried-hills in similar conditions in Bohai Bay Basin.