姬塬地区长8_1亚油层组浅水型三角洲砂体结构及成因

Sandbody structure and its genesis of shallow-water delta of Chang 8_1 reservoir in Jiyuan area,Ordos Basin

鄂尔多斯盆地姬塬地区长8油层组为浅水三角洲沉积,其储层具有横向变化快、非均质性强的特征。为了更好地表征储层非均质性,预测储层甜点区的分布,基于岩心资料和测井资料,结合现代沉积分析,对鄂尔多斯盆地姬塬地区长8_1亚油层组的砂体结构特征、成因和分布规律进行了研究。结果表明:研究区长8_1亚油层组砂体结构类型主要有4种,即叠合箱型(包括块状叠合箱型和层状叠合箱型)、齿化钟型、孤立箱型和孤立指状,其中叠合箱型、齿化钟型均表现为多期分流河道砂体叠置,是研究区主要的含油砂体;砂体结构成因、类型及分布与古构造、古地貌、基准面旋回、物源供给和古气候等相关。结合鄱阳湖现代三角洲沉积特征分析表明,研究区砂体为分流河道沉积,具有垂向交错叠置、平面连片分布的特征,该认识对鄂尔多斯盆地延长组油气勘探与开发具有参考价值。

Chang 8 oil reservoir set of Yanchang Formation in Ordos Basin belongs to shallow-water delta deposit,of which the reservoir changes rapidly and has strong heterogeneity. To identify the characteristics of reservoir heterogeneity and predict reservoir sweet spot in Jiyuan area,studies were performed on the structure characteristics,genesis and distribution of sandbodies of Chang 81 reservoir by using data from coring and well logging and modern sedimentary cases. The results show that there are four types of sandbody structure in this area,including composite funnel(block composite funnel and layered composite funnel),zigzag bell-shaped,isolated box and isolated finger sandbody structure. The former two types of sandbody structure are vmultiple superimposed by distributary channel and were the main oil-bearing sandbodies. The origin,type and distribution of sandbody structure are related to palaeotectonics,paleogeomorphology,base-level cycles,sediment supply and palaeoclimate. Based on the characteristics of modern shallow delta sedimentation in Poyang Lake delta,the sandbodies in the study area are multistage distributary channel deposition,which have the characteristics of superimposed reservoir vertically and sheet distribution in horizontal. This understanding will be helpful to oil and gas exploration and development of Yanchang Formation in Ordos Basin.