湖相滩坝砂体构型及对致密油甜点开发的意义——以柴达木盆地扎哈泉地区扎2井区为例

Study on sand body architecture of lacustrine beach-bar and significance for development of tight oil sweet areas:Case study of Well Za-2 area in Zahaquan area,Qaidam Basin

柴达木盆地扎哈泉地区上干柴沟组油藏具有储层物性差、非均值性强的特点,是柴达木盆地致密油的重要勘探区块。研究发现,滩坝是该区主要的沉积类型,弄清滩坝砂体的内部结构和空间展布对致密油甜点开发具有重要的指导意义。通过丰富的岩心、测井、分析化验、试油试采等资料,对扎哈泉地区滩坝沉积微相进行构型研究,探究其与致密油气分布的关系。扎哈泉地区上干柴沟组滩坝砂为滨浅湖亚相,进一步细分为坝中、坝缘、滩及浅湖泥4种微相。通过岩心标定测井,建立了相应的测井相模式,并总结出了稀疏井网条件下是否属于同一坝体的3个判断标准,即相邻坝体的高程差异、单一坝的相变、测井曲线形态差异。利用该技术手段在扎哈泉地区扎2区块Ⅳ-3小层识别出3期沉积的4个单一坝体,在Ⅳ-1小层识别出3期沉积的5个单一坝体。扎哈泉地区滩坝砂体主要存在砂体岩性尖灭型、单砂体孤立型、物性遮挡型3种砂体形态,坝中发育区带控制着致密油甜点的分布。

The upper Ganchaigou Formation reservoir in Zahaquan area of Qaidam Basin is an important exploration block for tight oil but has poor reservoir physical properties and strong heterogeneity.It is found that beach bar is the main sedimentary type in this area.It is important to understand the sand body architecture and spatial distribution of beach bar sand body for the development of tight oil sweet area.Based on the abundant data of core,logging,analysis,testing and production,this paper studies the sand body architecture of beach bar microfacies in Zahaquan area,and explores its relationship with the distribution of tight oil and gas.The beach bar Sands of Ganchaigou Formation in Zahaquan are shore and shallow lake subfacies,which are further subdivided into four microfacies:Dam,dam edge,beach and shallow lake mud.Through core calibration logging,the corresponding logging facies model is established.This paper summarizes three criteria for judging whether a dam is the same or not under the condition of sparse well pattern,namely,the elevation difference between adjacent dams,the phase change of a single dam and the shape difference of logging curves.Four single dam bodies of three-stage deposits were identified inⅣ-3 sublayer of block Za-2 by the techniques,and five single dam bodies of three-stage deposits were identified in Ⅳ-1 sublayer.There are three types of sand bodies in the beach bar sandbody of Zahaquan area:Lithologic pinchout sandbody,single sand body isolated sandbody and physical barrier sandbody.The Development Zone in the dam controls the distribution of tight oil sweet areas.