三湖地区七个泉组沉积相再认识与有利岩性圈闭预测

Re-understanding of Sedimentary Facies and Prediction of Favorable Lithologic Trap of Qigequan Formation in Sanhu Area

三湖地区七个泉组具有国内最大的生物气地质储量,但其沉积相一直存在争议,影响了对有利岩性圈闭的认识。从沉积相分析的角度入手,利用"相控岩性圈闭"的普遍规律,来预测有利岩性圈闭的发育区域。根据大量露头及岩芯观察,联合测井及地震数据,发现七个泉组内共有6大类沉积相,并非前人认为的那么简单,可细分为17个亚相和37个微相,其中,辫状河、辫状河三角洲相是首次识别,且非常关键;七个泉组时期,三湖地区总体呈现出"南陡、北缓"的地质格局。研究区南部发育多种沉积相,且相变快,而北部的沉积相发育很单一,范围也很局限。辫状河三角洲,尤其是前缘的水下分流河道,其内砂体厚度大、平面分布连续、物性好,是研究区最有利的储集砂体,平面上主要位于全吉、埃南及中灶火地区;3大滑塌成因的砂体,其周围被暗色深湖泥包裹,是天然的岩性圈闭发育地带,可形成良好的岩性油气藏,主要位于那北1井北部、台南5井南部及甜参1井周围,面积大,厚度大,应是研究区未来开展生物气精细评价的首选目标。

The Qigequan formation in Sanhu area has the biggest biological gas geological reserves in the domes- tic, but the sedimentary facies was unclear, which directly affected the knowledge of favorable lithologic trap. From the angle of analysis of sedimentary facies, the area of favorable lithologic trap will be predicted by the rules of ＂li- thologic trap facies controlled＂. Through the observation of amount of outcrop and cores, combine with data of seis- mic and logging, the Qigequan formation develops 6 kinds of sedimentary facies was found, which could be identi- fied into 17 subfacies and 37 microfacies, among them,the braided river,braided river delta facies were firstly iden- tified and being very important. During the period of sedimentation of Qigequan formation, the area had the geolog- ical background of ＂south steep,north slow＂ ,the type of sedimentary facies of the south was very rich and changed fastly. The braied-river delta, especially the underwater distributary channel should be the favorable reservoir sand- stones of research area, which developed in the Quanji, Ainan and Zhongzaohuo area; the 3 sand body of slump gravity flow developed in deep lake mudstone can form fine natural lithologic trap, which developed in the northern of Nabei 1 well, sourthern of Tainan 5 well and around of Tiancan 1 well, which should be the first target of the fu- ture biogas fine evaluation of Sanhu area.