断陷湖盆致密砂砾岩储层特征与成因  

Characteristics and Genetic Mechanism of Tight Sandy Conglomerate in Faulted Basin

作　　者：袁义东[1] 张金功[1] 刘林玉[1] 杨燕 张鹏[1] 刘燕妮 崔强[1] Yuan Yidong;Zhang Jingong;Liu Linyu;Yang Yan;Zhang Peng;Liu Yanni;Cui Qiang(Department of Geology, Northwest University, Xi＇an 710069, China;Research Institute of Exploration and Development of Changqing Oilfield, PetroChina, Xi＇an 710018, China)

机构地区：[1]西北大学地质学系,西安710069 [2]中国石油长庆油田分公司勘探开发研究院,西安710018

出　　处：《地质科技情报》2018年第2期192-198,共7页Geological Science and Technology Information

基　　金：国家科技重大专项(2017ZX05009-002)

摘　　要：徐家围子断陷是我国断陷湖盆致密砂砾岩气勘探区块之一,其下白垩统沙河子组是勘探的主力目的层,储层致密是该区致密气勘探亟需解决的关键问题。通过岩心观察、薄片分析、扫描电镜观测、压汞测试和物性统计,分析了下白垩统沙河子组砂砾岩储层的特征,从沉积、成岩角度讨论了储层致密的成因。研究表明,沙河子组砂砾岩储层主要为扇三角洲和辫状河三角洲沉积,储层物性差,具有低孔、低渗特征;储集空间具有孔隙-裂缝双介质特征,孔隙类型多为长石溶孔、岩屑溶蚀,孔隙结构复杂,缩颈型喉道和管束状喉道占主导地位,裂缝类型为压裂缝。储层特征受沉积和成岩作用共同控制,近源搬运背景下砂砾岩的成熟度低,高含量的塑性岩屑和泥质杂基不利于原生孔隙的保存,沉积物粒度和埋深决定了微裂缝的发育程度。成岩作用通过储层埋藏史影响储集物性,储层原生孔隙在早期快速深埋过程中大量减少,导致后期生烃流体运移不畅,限制了溶蚀作用的发育规模;同时,溶蚀期以后砂砾岩储层再次埋深并经历强烈的胶结作用,残余粒间孔和次生溶孔再次遭受破坏,最终形成低孔、超低渗致密储层。Xujiaweizi Depression, one of tight gas exploration blocks in China, contains sandy conglomerate reservoirs in lower Crataceous Shahezi Formation of the main exploration targets, where the reservoir tightness constrains the exploration. This paper analyses the characteristics of sandy conglomerate reser- voirs in Shahezi Formation of Xujiaweizi Depression by core observations, thin section analysis, scanning electron microscope observation, mercury penetration analysis, and reservoir physical property statistics, and also discusses the origin mechanism of tightness based on deposition and diagenesis. The results show that sedimentary facies of the sandy conglomerates are mainly fan delta and braided river delta, and that the reservoir physical properties are poor, belonging to low-porosity and low permeability reservoirs. The sandy conglomerates are dual porosity reservoirs with pores and fractures, while the reservoir spaces are corrosion pores of feldspar or debris. The pore structure is complex with throat type, mainly tubular and lamellar. Fractures are mainly developed in the rigid particles, which are mostly compressive cracks. Reser- voir characteristics are controlled by sedimentation and diagenesis. Sandy conglomerates are characterised by low maturity and rich in plastic debris and mud matrix, resulting in the poor initial reservoir quality. The grain size of sediments affects the development of microfractures. Diagenesis affects the pore evolution through burial history. In the early stage, a large number of the original pores were reducedby intense compaction, causing the weak acid fluid activity and dissolution. Meanwhile, residual intergranular pores and secondary dissolution pores were subjected to compaction and cementation.

关 键 词：致密 砂砾岩 储层 断陷 徐家围子 

分 类 号：P588.212.3[天文地球—岩石学] P588.212.5[天文地球—地质学]