摘要
滩坝砂体是陆相断陷湖盆缓坡带油气勘探的重要对象,对碎屑岩滩坝沉积体系的地质认识,传统上主要局限于湖盆边坡地带和水下古隆起等正向构造带。东营凹陷在中国东部箕状断陷盆地中最具代表性,从其缓坡带勘探实际来看,已发现沙四段滩坝砂储层分布范围并非严格受古鼻状构造控制,传统的古水下隆起控砂模式不能很好地解释该区滩坝砂体展布特征。由于滩坝砂体以砂泥薄互层为特征,单层厚度薄,横向变化大,分布规律复杂,储集砂体的地质识别与描述以及地球物理预测难度均较大。因此研究滩坝砂体沉积特征、展布规律及预测方法不但具有理论意义,而且对深化类似区带油气勘探也具有重要实际意义。
综合利用钻井岩心、地震、测井等资料,对东营凹陷沙四上亚段滩坝砂体沉积特征、成因机制进行了系统性研究,认为沙四上亚段可分为1个三级层序和3个体系域,滩坝砂体主要形成于三级层序的低位域;根据滩坝砂的形态、结构、产状及分布特征,可划分为坝砂和滩砂亚相。古地貌、古物源、古水动力、古基准面共同控制了滩坝砂体的形成和分布;其中,古地貌控制滩坝砂的发育分布范围,古物源控制滩坝砂的发育程度,古水动力控制滩坝砂的相带展布,古基准面控制滩坝砂的叠置样式。
在滩坝砂体薄储层预测方面,提出了基于滩坝砂体成因层序特点的地质-地球物理综合预测方法。首先,通过层序地层研究,明确滩坝砂体发育层位;其次,通过古地貌-古环境匹配研究确定滩坝砂体发育区带;再运用综合地球物理技术,根据滩坝砂体的地质-地震响应特征,选择针对性的储层预测方法和地震属性参数组合,通过井震结合精细描述滩坝砂体。应用该方法,对东营凹陷沙四段滩坝砂体的预测取得了良好效果。实践证明,地质分析与地球物理技术的综合应用是预测描述薄互层储层的有效途径。
The beach-bar is main exploration target in the shelving of nonmarine downfaulted basin. Traditionally, the depositional system of clasolite beach-bar is thought localizing in slope of lake-basin and palaeohigh underwater. Dongying sag is a typifier of half basin in China east. By exploration practice, it is found out that the distribution of beach-bar of Es4 is not only controlled under nosing structure, and it is disagreement with traditional idea. Hence it is very important the study of forming and distribution of beach-bar. Being aimed at difficulties of beach-bar of Es4 in Dongying sag, the comprehensive research is done by present sedimentology, high definition sequence stratigraphy and geophysical technology. The sedimentary characteristics and identification mark and distribution of beach-bar in Dongying sag are clearly and definitely. On base of the geologic model, the relationship of geologic framework and seismic response is built up by forward modeling. The comprehensive predict method of beach-bar is built up and practiced in exploration, and the good effect is acquired.
Using the data of drilling core, seismic and logging, the sediment features and origin mechanisms of beach bar sand-body. in Dongying sag are researched systemically, the writer thinks that there are one third sequence and three system fields, the beach bar sand-body mainly forms in low order fields of third system fields. The beach bar sand-body is classified into beach dam sands and bank sands. Palaeogeomorphology, Palaeosource, Palaeohydropower and Palaeobasal-level controls forming and distribution of beach bar sand-body. Palaeogeomorphology controls the distribution and Palaeosource controls the development level and Palaeohydropower controls facies belt distribution and Palaeobasal-level controls overriding styles.
A case study of E2s4 in Dongying depression, it is put forward that the comprehensive prediction method of geology- geophysics based on the genesis features of beach bar sand-body. Firstly, by researching stratigraphic sequence the distribution areas of beach bar sand-body are known; secondly, analyzing response characters of geology-seism, effective reservoir prediction methods and seismic attribution parameters are chosen; finally, favorite facies belts are understood by multi-attribution analyzing of target stratum and the beach bar sand-body is described by linking well and seism. Using of this method, well effects are gained in predicting beach bar sand-body of E2s4 of Dongying depression. It indicates that the comprehensive uses of geology analyzing and geophysics skills is effective to predict and descript the reservoirs of beach bar sand-body.
引文
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