辽河坳陷大民屯凹陷沙四段页岩油“甜点”预测及评价

Prediction and evaluation of sweet spots for shale oil in Es_(4)of Damintun Sag,Liaohe Depression

以往按照致密油勘探的技术思路研究大民屯凹陷沙四段页岩油,存在以下问题:一是油页岩作为沙四段页岩油领域的烃源岩,更多地关注其生烃能力,而忽视了其自身的储集能力;二是常采用波阻抗反演和地震属性分析等常规技术宏观预测地质“甜点”,结果存在多解性;三是尚未开展与工程“甜点”(储层脆性、裂缝等)相关的参数预测。为此,综合应用地质资料,以岩石物理分析为依据,确定了以源岩品质、储层品质及工程品质为主要的评价要素,并建立主要评价要素与地球物理响应参数之间的关系模型;利用“两宽一高”地震资料,分层组、分要素精准预测了页岩油“甜点”分布,形成了一套针对陆相页岩油“甜点”的地球物理预测方法和技术流程。得到以下认识:Ⅰ组以油页岩为主,以寻找富有机质油页岩为目标,TOC值预测是重点;Ⅱ组以泥质云岩为主,储层物性相对较优,溶蚀缝发育,储层岩性及裂缝预测是关键,储层脆性指数预测也是重点;Ⅲ组下段以寻找优质砂体、上段以寻找稳定的泥质云岩为目标,储层岩性预测是关键。

In the past,shale oil in the fourth member of Shahejie Formation(Es_(4))in Damintun Sag was studied by the technical ideas of tight oil exploration.This way of exploration,however,faces the following problems.First,as oil shale is the source rock of Es_(4),we pay more attention to its hydrocarbon generation capacity but neglect its reservoir capacity.Second,we often use conventional techniques such as impedance inversion and seismic attribute analysis to predict the geological sweet spots,but the results are multi-solution.Third,the parameters related to the engineering sweet spots(reservoir brittleness,fractures,etc.)have not been predicted yet.Therefore,on the basis of the comprehensive application of geological data and petrophysical analysis,the main evaluation factors of source rock quality,reservoir quality,and engineering quality are determined,and the relational model between main evaluation factors and geophysical response parameters is built.Given the seismic data of“wide azimuth,Wide broadband,and high density(WBH)”,this study accurately predicts the distribution of sweet spots for shale oil in groups and factors and hence,forms geophysical methods and a technical process for predicting the sweet spots of terrestrial shale oil.The following knowledge is obtained:Group Ⅰ is dominated by oil shale,aiming to search for organic-rich oil shale,and TOC value prediction is the key point.Group Ⅱ is dominated by argillaceous dolomite,with excellent reservoir physical properties and developed dissolved fractures;the prediction of reservoir lithology and fractures is the key,and the prediction of the reservoir brittleness index is also important.The lower part of Group Ⅲ is to look for high-quality sand bodies,and the upper part is to look for stable argillaceous dolomite;the lithology prediction of reservoirs is the key.