玛湖凹陷百口泉组砂砾岩建筑结构要素层次分析

Hierarchical Architectural Element Analysis for Sandy Conglomerate Deposits of Baikouquan Formation, Mahu Sag

2010年以来,在准噶尔盆地玛湖凹陷下三叠统百口泉组勘探发现了巨大的油气资源,但由于百口泉组砂砾岩内部结构复杂,储集层非均质性强,给油藏评价和高效开发带来了困难,需要对砂砾岩体的沉积成因和建筑结构进行深入分析。运用建筑结构要素层次分析法,对玛湖凹陷百口泉组砂砾岩的建筑结构进行了解剖。通过对82口取心井1 922 m岩心的详细描述,提出了以岩石粒度、沉积构造、颜色和颗粒支撑方式等4种属性为主的多属性岩石相命名方案,在百口泉组砂砾岩中识别出227种岩石相类型。依靠岩心、测井和地震信息,在研究层段划分了11级沉积界面。与11级沉积界面相对应,划分了11级建筑结构要素,重点对与岩石相和沉积微相对应的建筑结构要素进行了分析。以第9级建筑结构要素为基本单元,通过地震资料约束下的连井对比,刻画了黄羊泉扇和夏子街扇的沉积体系演化过程,认为黄羊泉扇和夏子街扇百口泉组皆为一套砂砾岩粗粒沉积,都以河流为主要搬运动力,但黄羊泉扇沉积体系较短,具有更多冲积扇和洪积扇的特征,夏子街扇沉积体系规模大,更具有河流扇的特征。从百一段到百三段,随着湖泊水位上升,沉积体系从冲积扇和河流扇,逐渐退缩演变为扇三角洲。杂基含量低的中细砾岩是良好的储集岩石相,季节性河道沉积、水下分流河道沉积是有利的储集微相,百二段是油层最发育的有利层段。

Enormous petroleum resources have been discovered in the Lower Triassic Baikouquan formation of Mahu sag, Jungar basinsince the year of 2010, but reservoir evaluation and efficient development are difficult due to the complicated internal structure and seriousreservoir heterogeneity of the sandy conglomerate in Baikouquan formation, so profound analyses on sedimentary genesis and architecturalstructure of the sandy conglomerate are needed. The paper utilizes hierarchical architectural element analysis method to delineate the archi-tectural structure of the sandy conglomerate in Baikouquan formation of Mahu sag. Based on the detailed description of cores of 1,922 mlong obtained from 82 wells, the paper presents a multi-attribute lithofacies denomination program which is dominated by 4 attributes i.e.,rock grain size, sedimentary structure, color and grain support mode and 227 lithofacies are identified in the sandy conglomerate of Baik-ouquan formation. According to core, logging and seismic data, depositional interfaces of 11 orders are classified in the studied interval andarchitectural structural elements of 11 orders are identified correspondingly, and the corresponding architectural structural elements tolithofacies and sedimentary microfacies are analyzed. Taking the 9 th order architectural structural element as a basic unit, the evolutionprocesses of the sedimentary systems in Huangyangquan fan and Xiazijie fan are characterized through well-tie correlation constrained byseismic data. It is considered that the Baikouquan formation in both Huangyangquan fan and Xiazijie fan belongs to coarse-grain sandy con-glomerate deposits and takes river as the main transportation force. The depositional system of Huangyangquan fan is of relatively smallscale and has more characteristics of alluvial fans and fluvial fans; the depositional system of Xiazijie fan is of large scale and has morecharacteristics of river fans. From the first member to the third member of Baikouquan formation, the depositional system graduallychanged from alluvial and fluvial fans to fan delta with the rise of water level of lake. Medium-fine conglomerate with low content of matrixis good lithofacies, seasonal channel deposits and underwater distributary channel deposits are favorable sedimentary microfacies, the sec-ond member of Baikouquan formation is the most favorable interval for oil accumulation.