子长—蟠龙地区长1半深—深湖相沉积及其生油意义

目的研究子长—蟠龙地区长1油层组对本区油藏形成的影响。方法利用钻屑、测井、露头观察及化验资料等综合分析本区长1油层组的沉积特征和生烃能力。结果子长—蟠龙地区上三叠统延长组长1段上部(T3y55)广泛发育深湖相暗色泥岩、油页岩及浊积岩,其下伏为长1中下部交织河沉积,二者之间发生了一次突然水进,形成了10～15 m的深湖相泥岩、油页岩,其下沉积的为60～100 m的半深湖粉砂泥与浊积岩沉积。湖相沉积顶部被侏罗系延安组砂岩侵蚀切割,二者之间为平行不整合接触。从暗色泥岩厚度图可以看出,子长—蟠龙地区湖相东西宽度60 km,南北长120 km,且该区仅为原始湖泊的东半部中间部分,原始湖泊的面积应向南、西、北3个方向延伸至少两倍以上的面积。长1暗色泥岩有机质丰度高,有机碳含量大于4%,多为II1型干酪根,达到成熟阶段,因而具较好的生烃能力。结论该区广泛发育的长1湖相烃源岩对于盆地广大地区长2和侏罗系油藏的形成都具有重要意义。

Chang 1 lacustrine sediments and oil-source-rock conditions in Zichang-Panlong Area

Aim To study the impact of Chang 1 in Zichang-Panlong Area on this area′s oil reservoir.Methods Based on comprehensive analysis of cuttings debris,logging,outcrop observation and laboratory data,etc,a research is maded on the sedimentary characteristics and the hydrocarbon generation capacity of Chang 1.Results The analysis of depositional evidences suggests that Chang 1 of Upper Triassic Yanchang Formation contains sediments of deep-water lacustrine dark shale,oil shale and turbidites.The lake was caused by an abrupt transgression over depositions of anastomosing river,which led to an accumulation of 10~15 m deep lacustrine shales.Following them is the deposition of 60~100 meters of semi-deep lacustrine silt,mud and turbidites.The uppermost of the lacustrine sediments were locally eroded and degraded by a Jurassic Yan′an incised valley related to a disconformity between Triassic and Jurassic.The isopach map of dark shales indicates that the lacustrine facies in Zichang-Panlong region lengthen north-south 120 km and widen east-west 60 km.Moreover,the study area is only the middle part of the eastern original lake which should extend westward,northward and southward much more distances and cover double area of the present defined lacustrine portion.Chang 1 dark shales possess rich organic matter and the organic carbon is more than 4%.Most of them belong to II1 type of kerogen which has evolved to the maturated period.Therefore the lacustrine rocks conform to the conditions of high quality of oil source rocks.Conclusion The widespread Chang 1 lacustrine rocks may have great significance to the information of Chang 2 and Jurassic reservoir in Ordos Basin.