一种辫状河心滩砂体构型解剖新方法

辫状河构型解剖注重在单井上识别心滩砂体,而在平面上刻画心滩砂体时则随意性较大,从而降低了解剖结果的准确性。为此,在解剖露头剖面及现代辫状河沉积原型模型的基础上,对心滩内部落淤层发育位置、各构型单元的接触关系进行了研究。根据该关系,以鄂尔多斯盆地苏里格气田苏X加密井区中二叠统石盒子组8段下亚段(以下简称盒8下亚段)辫状河砂体为例,利用测井、录井、岩心等资料划分河道砂体构型单元、精确定位单井钻遇心滩的位置,进而形成了地下辫状河砂体构型解剖方法,并应用于气田开发钻井。结果表明:(1)落淤层的发育与心滩部位关系密切,心滩不同部位垂向微相叠置规律性强,可作为辫状河储层构型解剖的重要参考;(2)辫状河砂体构型单元包括心滩、辫流水道和泛滥平原3类,其中心滩砂体是主要的成藏单元;(3)苏X加密井区盒8下亚段平面上呈"滩道相间、宽滩窄道"的沉积格局,不同沉积类型的砂体规模存在差异,其中心滩砂体宽度介于250~300 m,长度介于500~900 m;(4)验证井SX-1井钻遇2个心滩砂体和1个辫流水道砂体,钻遇的心滩个数、规模及心滩与辫流水道位置关系和新方法识别成果相吻合。结论认为,以"测井响应特征、落淤层发育位置以及垂向微相叠置模式"为标志的心滩砂体空间定位的储层构型表征新方法,能够准确确定心滩砂体平面分布位置,有助于揭示辫状河心滩砂体空间展布规律,提高心滩砂体构型表征结果的可靠度。

A new architecture characterization method for braided river channel bar sandbody

At present, the architecture characterization of braided rivers mainly focuses on the identification of channel bar sandbody in a single well, and the depiction of channel bar sandbody in plane is more random, so the accuracy of analysis results is reduced. In this paper, the outcrop section and the proto type model of modern braided river sediment were analyzed. Then, the development location of silt layer inside channel bar sandbody and the contact relationships between different architecture units were investigated. Finally, the braided river sandbody in the lower submember of 8th Member, Shihezi Fm, Middle Permian (P2x8L) in the Su X infill well block of the Sulige Gas Field, Ordos Basin, was taken as the study object to classify the architecture unit of channel sandbody and locate the drilling position of channel bar in the well accurately according to the contact relationships between different architecture units, combined with well logging, mud logging, core and other data. In this way, the architecture characterization method for underground braided river sandbody was developed and applied to the development and drilling of gas field. And the following research results were obtained. First, the development of silt layer is in close relationship to the position of channel bar, and vertical superposition of microfacies at different positions of channel bar presents strong regularity, so it can be used as an important reference for analyzing the architectures of braided river reservoirs. Second, the braid river sandbody consists of 3 architecture units, i.e., channel bar, braided channel and flood plain, among which channel bar is the main hydrocarbon accumulation unit. Third, in plane, P2x8L in Su X infill well block is in the sedimentation pattern of "channel bar alternating with braided channel, wide channel bar and narrow braided channel". The sandbodies with different sedimentation types are different in size. And the channel bar sandbody is 250–300 m wide and 500–900 m long. Fourth, in the verification well (Well SX-1), two channel bar sandbodies and one braided channel sandbody are encountered. The number and size of the encountered channel bars and the relationship between channel bar and braided channel are consistent with the analysis results provided by the new method. In conclusion, this new reservoir architecture characterization method for spatial location of channel bar sandbody, which takes "logging response characteristics, silt layer development location and vertical microfacies superposition mode" as the mark can be used to determine the distribution location of channel bar sandbody in plane, and it is beneficial to reveal the spatial distribution laws of braided river channel bar sandbody and improve the reliability of channel bar sandbody characterization results.