川东北地区二叠系—三叠系礁滩相储层发育机理

Development Mechanism of Permian- Triassic Reef Shoal Reservoir in Northeastern Sichuan Basin

川东北地区二叠系—三叠系天然气藏的规模受礁滩相储层发育程度的控制。为此,分析了川东北地区古地貌特征,并总结了古地貌背景下礁滩相储层差异发育的机理。研究发现:开江—梁平陆棚的形成与消亡控制着礁滩相储层的沉积演化。长兴组晚期,开江—梁平陆棚构造幅度最大,陆棚两侧礁滩相储层最发育;其他时期,开江—梁平陆棚构造幅度相对较小,陆棚两侧多数地区只发育台地边缘浅滩相储层。不同台地边缘坡度控制着礁滩相储层的发育模式。坡度越大,礁滩的垂向加积特征越明显,礁滩厚度越大,礁后浅滩与礁后礁越不发育,礁滩的面积越小。该研究对川东北地区二叠系—三叠系大中型天然气的勘探具有重要的意义。

The scale of Permian- Triassic gas reservoir in Northeastern Sichuan Basin is controlled by the development level of reef shoal reservoir. Therefore,in this paper,we analyzed the palaeogeomorphologic features of Northeastern Sichuan Basin,and summed up the mechanism of differential development of reef shoal reservoir under the palaeogeomorphologic setting. It was discovered through study that the formation and extinction of Kaijiang- Liangping Shelf controlled the sedimentary evolution of reef shoal reservoir. At late stage of Changxing Formation,the structural amplitude of Kaijiang- Liangping Shelf was the maximum,and reef shoal reservoir was mostly developed at both sides of the shelf; whereas at other stages,the structural amplitude of Kaijiang- Liangping Shelf was relatively small,and only platform edge shoal reservoir was developed in most areas at both sides of the shelf. The platform margin slope controlled the development pattern of reef shoal reservoir. Generally,the higher the slope,the more apparent the vertical accretion feature of reef shoal becomes,the thicker the reef shoal is,the more underdeveloped the backreef shoal and backreef reef are,and the smaller the reef shoal area is. In a word,the development and evolution of Late Permian- Early Triassic Kaijiang- Liangping Shelf and palaeogeomorphologic features of platform margin in Northeastern Sichuan Basin controlled the differential development of reef shoal reservoirs.