准噶尔盆地玛湖凹陷八道湾组一段沉积微相特征——以TX1井区为例

Sedimentary microfacies of the first member of Badaowan Formation in Mahu SAG, Dzungar Basin: Taking well TX1 as an example

关键词:  辫状河三角洲  平原亚相  前缘亚相  沉积分布

Key words:  braided river delta  plain subfacies  front subfacies  sedimentary distribution

摘要:

通过岩石学、沉积学及测井等方法，对准噶尔盆地TX1井区侏罗系八道湾组一段进行详细研究，认为侏罗系八道湾组一段主要发育复成分砾岩、砾状砂岩及砂岩，煤夹层；沉积构造发育，兼具水上及水下沉积的特点，发育粒序层理、中大型交错层理及冲刷充填、植物枝干印模等沉积构造；测井上具箱型、漏斗型、指状、线性等响应。沉积相纵向上逐渐向盆地边缘退积演化，其中三角洲平原亚相在2~5砂组较为发育，以辫状分流河道及河道间的河漫沼泽沉积为主，前缘亚相在1砂组较为发育，以水下分流河道及支流间湾沉积为主。辫状河三角洲前缘水下分流河道微相是最有利的储集相带，孔渗结构较优，原油含水率低；辫状河三角洲平原分流河道微相次之，其储层非均质性强，原油含水率较高。

Abstract:

Based on the detailed study of the first member of the Jurassic Badaowan Formation in TX1 well in Dzungar basin, it is considered that the first member of the Jurassic Badaowan Formation is mainly composed of polygenetic conglomerate, conglomerate-like sandstone, sandstone, and interbedded coal layers. The first member of the Jurassic Badaowan Formation develops abundant sedimentary structures such as grain sequence beddings, middle to large scale cross beddings, erosion fillings, and plant stem impressions. Well log shows box-type, funnel-type, finger-type and linear in shape. The sedimentary facies gradually retrograded to the margin of the basin in the longitudinal direction, in which the plain subfacies developed from No. 2 to No.5 sand formations dominated by braided distributary channel and interchannel fluvial marsh deposits. The front subfacies developed in No.1 sand formation, which is mainly composed of underwater distributary channels and intertributary bays. The subaqueous distributary channel microfacies in the braided river delta front are the most favorable reservoir facies zones, which are with better porosity and permeability. The microfacies of distributary channel in braided delta plain, are the second-class reservior, whose nomogenity is somewhat bad and the water/oil rate is high.