沾化凹陷罗家地区沙四段顶部至沙三段泥质岩裂缝特征及其影响因素

CHARACTERISTICS OF FRACTURES IN ARGILLACEOUS ROCKS OF LUOJIA AREA IN ZHANHUA SAG

利用岩心观察、岩石薄片鉴定和扫描电镜分析等技术手段 ,结合岩相古地理分析和古构造应力场模拟试验成果 ,对沾化凹陷罗家地区泥质岩裂缝的类型、特征、受控因素以及对油气储集的有效性进行了研究。结果表明 ,以张裂缝为主的顺层缝的长度、密度和开度大于切层缝 ,且为烃类的主要储集空间 ;包括张裂缝和剪裂缝在内的切层裂缝作为主要连通顺层裂缝的通道 ,很少储油。成岩收缩缝在泥质岩层中是极有利的油气储集空间 ,特别是在构造裂缝不太发育的地区 ,由成岩收缩造成的层间缝会成为主要的储集空间。裂缝发育的受控因素有区域构造应力、构造部位及其与断裂带的距离、岩性、岩相、地层厚度、物性、埋深和地层压力。预测研究区地层埋深为 2 2 0 0～ 340 0m ,在距离断裂带较近地区、断层转换带、凹陷斜坡坡度突变区、地层厚度和 /或砂岩厚度突变区、三角洲前缘亚相、湖底扇相砂体与湖相泥质岩交界过渡带 ,泥质灰岩、灰质泥岩、油页岩和油泥岩最有可能形成有效的裂缝储集空间。

The types, characteristics, influencing factors of fractures and reservoir properties were studied by means of analyses on cores and thin-section rock, scanning electron observing, facies analyses and paleo-stress field simulation, as the fractures were the main reservoir spaces of argillaceous rocks. The analyses show that the length, density and opening of factures in bedding joints are better than those in cutting bed joints. The bedding joints are the main reservoir spaces for hydrocarbon accumulation. Cutting bed joints are mainly the migration pathways for connecting bedding joints and have little reservoir petroleum. The diagenetic shrink fractures are the favorable reservoir spaces in argillaceous rocks, especially in the areas where few or no structural fractures were developed. The influencing factors for fracture growth include tectonic stresses, lithology, facies, formation thickness, porosity, formation depth and pressure. It is forecasted that the fractures tend to grow in the formation of 2200 m to 3400 m in depth. The argillaceous limestone, calcareous mudstone, oil shale and oil mudstone distributed in the transform zone, abruptly changed slope grade, transition area of delta front and sublacustrine fan with lake facies argillaceous rocks near the faults are available spaces of fractured reservoir possibly.