东营凹陷盐家地区沙四段砂砾岩储层裂缝发育特征

Development characteristics of glutenite reservoir fractures of the fourth member of Shahejie Formation in Yanjia area, Dongying sag

通过岩心观察、薄片鉴定、成像测井及物性分析等手段对东营凹陷盐家地区沙四段近岸水下扇沉积砂砾岩储层裂缝发育特征进行研究。研究结果表明:研究区沙四段砂砾岩储层裂缝普遍发育,主要为构造裂缝和风化缝、成岩缝、超压缝、溶蚀缝等非构造裂缝。有效的构造裂缝主要形成于东营期末强烈的构造反转活动,为挤压应力作用下的产物,近东西走向;这些构造裂缝以斜交缝为主,裂缝线密度随岩石粒度变粗和单层厚度增大而明显减小,总体上以近岸水下扇中扇辫状沟道和沟道前缘的中粗砂岩构造裂缝最为发育。风化缝主要发育于沙四上亚段内扇近岸水下扇主沟道和中扇辫状沟道微相的花岗片麻质中粗砾石中,是其在风化带遭受风化破裂和差异溶蚀所致,这类裂缝多开启并与孔隙连通,常储集油气。成岩缝在本区主要为压裂缝和收缩缝,压裂缝主要表现为粒内压裂缝和粒缘缝,其发育程度与岩石粒级、碎屑颗粒成分以及填隙物含量关系密切,在中扇辫状沟道颗粒支撑的粗砂岩和中细砾岩中最为发育。研究区沙四段异常超压较为普遍,造成胶结致密砂砾岩储层超压裂缝较为发育。粒度较粗、颗粒支撑、单层厚度适中的中扇亚相辫状沟道砂砾岩中各类裂缝较为发育,与孔隙交织在一起构成连通性良好的孔隙-裂缝复合储集空间系统,是其成为近岸水下扇中最有利的储集相带的重要原因。

Development characteristics of glutenite reservoir of nearshore subaqueous fan fractures of the fourth member of Shahejie Formation, Paleogene in Yanjia area of Dongying sag were studied based on the comprehensive analysis of cores, thin sections, FMI loggings and physical properties analysis. The results show that there are abundant structural fractures and non-structural fractures, such as weathering fractures, diagenetic fractures, overpressure fractures and dissolution fractures in the glutenite. Effective structural fractures in Yanjia area are induced by the compression stress, due to the intense structural inversion in the end of Dongying Formation stage. Most of these structural fractures are oblique. Linear fracture density decreases with the grain sizes coarsening and the layer thickening. Middle-coarse sandstone fractures are mostly developed in general. Weathering fractures are mostly open and connected with the pores in granite gneiss pebbles and cobbles of main channels and braided channels. Diagenetic fractures in Yanjia area mainly include crashed fractures and shrink fractures. Diagenetic compaction induces crashed fractures which include intra-grain fissures and grain edge fissures, common in grain supported coarse sand and conglomerate of braided channels, the development degree of which is closely related to the grain size, clastic particles component and the interstitial material content. Overpressure fractures are promoted by the available overpressure common in Yanjia area. Fractures are relatively well developed in braided channels of middle fan, which has coarser-grained and grain supporting texture and moderate layer thickness. The cracks and pores are intertwined forming pore-fracture complex reservoir space, which is the important cause of being the most favorable reservoir of nearshore subaqueous fan.