青海油砂山油田第68层分流河道砂体解剖学

青海油砂山剖面第６８层三角洲分流河道砂体内部可识别出来Ｇｐｒ、Ｇｌｔ、Ｇｅ、Ｓｌｔ、Ｓｍｔ、Ｓｐｒ、Ｓｌａ、Ｓｂｍ、ＳＩｃｒ、ＳＩｈ和Ｍｒｉ等１２种岩石相，它们构成了６种岩石相组合，即:Ｇｅ－Ｇｐｒ－Ｇｌｔ组合，Ｇｌｔ－Ｓｌｔ组合，Ｓｌｔ－Ｓｍｔ组合，Ｇｌｔ－Ｓｂｍ组合，Ｓｓｔ－Ｍｒｌ组合，Ｇｐｒ（Ｓｐｒ）－Ｍｒｌ－Ｓｓｔ－Ｍｒｌ－ＳＩｃｒ－Ｍｒｌ组合。按照沉积界面之间的切割关系，建立一个包括７级界面的界面层次，第一级为砂体的上下边界，第七级为纹层边界，沉积界面将砂体分隔为三个沉积幕，它们由六个沉积亚幕组成。砂体建筑结构要素包括侧积体（ＬＡ），纵向砂坝（ＬＢ），横向砂坝（ＴＢ），简单砾质充填（ＧＦ），简单砂质充填（ＳＦ）和堤岸砂坪（ＬＦ）等六种类型，它们具有不同的宽度和厚度比。通过露头密网格采样和沉积学分析建立了砂体渗透率原型模型，均质模型，幕式模型以及建筑结构要素模型，其中建筑结构模型与原型模型相似性最好，证明了利用建筑结构分析可以建立符合砂体客观实际的储层地质模型。

Anatomy of Distributary Channel Sand, the No.68 Sandbody of Youshashan, Western Qinghai

The bottom of the lower Youshashan Formation (Neogene) was deposited by a braided deltaic system. The No.68 sandbody was a distributary channel cut into the exposed lake bed during the lower stand stage. Sediments of the sandbody were transpoted by the longitudinal braided deltaic system located between the Qimantage and Argin mountains. The No.68 sandbody has the similar upward thinning structure and grain size sequence as most of fluvial sandbodies have. 3D sampling net work controls 158 meters long of the sandbody. The sandbody is 42.5 meters wide and 5.33 meters thick, it widens and thins toward the downstream, which is also one of the common characters of all deltaic front distributary channels. We recognized 12 lithofacies within the sandbody, they are: Gpr, Glt, Ge, Slt, Smt, Spr,Sla,Sbm, Sst, SIcr, SIh, Mr1. 6 lithoracies assemblages are composed of the 12 lithofacies, they are: Ge-Gpr-Glt; Glt-Slt; Slt-Smt; Glt-Sbm(Spr); Sst-SIt, SIcr(Gpr,Spr,Sst)-Mrl. There are 6 kinds of architectural elements in the sandbody, they are: lateral accretion(LA), longitudinal bar(LB), transverse bar(TB), simple gravel filling(GF), simple sand filling(SF), levee and sandflat(LF). LA is 8.8 14.4 m wide and has the ratio of width/thichness(W/T) 5.5 7.2, LB is 10 12.4 m wide and its W/T is 4.17 5.17, TB is 6.4 m wide and its W/T is 2.67, GF is 30 m wide and its W/T is 40, SF is 12 24 m wide and W/T is 15 30, LF is 1.76 m thick. LA,LB and TB are situated at the lower part of the sandbody, GF and SF develop at the upper part of the sandbody, LF occurs at the two channel banks. A 7 order surface hierarchy in the sandbody has been found in accordance with the sedimentary events. First order is the top and bottom surface of the sandbody, second order is sedimentary phase surface, third order is the surface of sub-phase, fourth order shows the surface of died channel bars, fifth order surface is the accretion surface within bars, sixth order represents the cross bedding set surface and the seventh order is the surface of laminar. By the surface hierarchy, the depositional process of the sandbody was reconstructed by 3 sedimentary phases and 6 sub-phases. Compared the architectural element reservoir model with the thin grid proto-type reservoir model, it could be concluded that the two models are very similar in permeability distribution. This tells us that we can build the predictable reservoir model using the method of architectural element analysis, with the predictable model we can predict remaining oil distribution and provide more useful information for EOR.