四川盆地川中地区侏罗系沙溪庙组不同类型砂体地质特征及地震精细雕刻

Geological characteristics and seismic fine description of different types of sand bodies in Jurassic Shaximiao Formation in central Sichuan Basin

四川盆地侏罗系湖泊—河流沉积体系中的砂体是目前浅层致密油气勘探开发的现实对象。由于受沉积微相影响,砂体具有类型多样、岩性多变、厚度变化大、非均质性强等特点,因此预测困难。通过对侏罗系沙溪庙组沙一段砂层组类型的划分,开展了不同类型砂体的储层分析,指出了不同类型砂体的测井、地球物理响应特征,分时窗对不同类型砂体进行了精细识别和空间预测。研究表明:①沙一段可划分为5个砂层组,其中第一砂组主要为滨浅湖相席状砂、滩坝砂,2~5砂层组为三角洲前缘—平原相河道砂;②河道砂平均孔隙度为4.68%,明显高于底部席状砂孔隙度的3.1%,且Ⅰ期河道砂物性最好,其次为Ⅳ期、Ⅱ期、Ⅲ期河道砂;③河道砂的预测标准为自然伽马小于65 API,席状砂的预测标准为自然伽马65~75 API。砂体预测中,针对席状砂(滩坝)将研究时窗提取到0~20 ms以内;针对河道砂将研究时窗划分在沙底向上20~100 ms范围内。最终建立起了一套适用湖泊—河流沉积体系中不同类型砂体精细刻画与预测的方法。

Sand bodies in the Jurassic lacustrine-fluvial sedimentary system in the Sichuan Basin are realistic objects of shallow tight oil and gas exploration and development.Due to the influence of sedimentary microfacies,sand bodies have geological characteristics such as type diverse,variable lithology,significant thickness variation,and strong heterogeneity.Therefore,the fine description and prediction of different types of sand bodies is the current bottleneck for exploration and development.Based on the classification of various sand group types of the 1st member of Jurassic Shaximiao Formation,reservoir analysis was carried out,logging and geophysical response characteristics were concluded,and fine identification and spatial prediction were made by time-sharing window.Results show that:(1)The 1st member of Shaximiao Formation can be divided into 5 sand groups,among which the 1st sand group is mainly littoral-shallow lacustrine sheet sand and beach bar sand,and the 2nd to 5th sand groups are delta front facies channel-plain channel;(2)The average porosity of channel sand is 4.68%,which is significantly higher than that of bottom sheet sand(3.1%).The physical properties of theⅠchannel are the best,followed by theⅣ,Ⅱ,andⅢchannels.(3)The prediction standard of channel sand is:natural gamma<65 API,and the prediction standard of sheet sand locates between 65 and 75 API.In sand body prediction,for sheet sands(beach bars),the study time window is extracted to be within 0-20 ms,and for river channels,the study time window is in the range of 20-100 ms upwards from the bottom of the Shaximiao Formation.Finally,a set of methods suitable for fine description and prediction of different types of sand bodies in the lacustrine-fluvial sedimentary system was established.