上扬子台地晚二叠世礁相油气藏的断块构造控制与勘探方法建议

Control of fault blocks upon the Late Permian reservoirs of reef facies in the Upper Yangtze Platform and exploration suggestions

从构造作用最重要的沉积记录入手,结合大量玄武岩成线状、面状喷溢,同生断层发育,表层褶皱、断裂构造形迹体系与台地断块间存在相互制约关系等进行研究,发现上扬子台地从形成到结束历经3次大落大起、无数次强烈撕裂和2次大规模撕裂,并造成部分地区的大幅沉降,形成若干条台内台沟等景观。台地东半部从北到南形成大巴山前缘断块、华莹山断块、东部台缘断块、永川-宜宾断块、赤水-古道-盐津断块、毕节-镇雄断块、黔西-大方断块、织金-纳雍断块和普定-普安断块等9个断块,并首次绘制出第一幅断块格杂图。断块间彼此作不平衡升降运动,其结果造成断块一端高跷,抬升侧控制着生物礁的生长发育和白云岩的形成,最后形成礁控油气藏。晚二叠世时,大巴山前缘断块是西端高跷、东部低垂,南侧抬升、向北掀斜;华蓥山断块和东部台缘断块均是北部高跷、南部低垂,东侧抬升、向西掀斜。在此基础上提出,勘探礁控油气藏应遵循:①断块构造控制;②由高跷端向低垂端、由抬升侧向掀斜侧顺序施钻;③断块掀斜不明,生物礁发育不清,应先做沉积相分析对比,切勿盲目上钻。

In the Upper Yangtze Platform, a large amount basalt show linear and planform eruption, contemporaneous faults are well developed, and mutual restrictive relationship exists between epidermic fold and fracture trace systems and fault blocks. Study of sedimentary records in combination with these observations shows the platform during its formation experienced three drastic up- and down-turns, countless strong tearing and two large-scale tearing, causing strong subsidence in some areas and the formation of several intraplafform troughs. In the eastern part of the platform, nine fault blocks are recognized from north to south, namely Dabashang frontal fault block, Huayinshan, eastern platform margin, Yongchuan-Yibin, Chishui-Gudao-Yanjin, Bijie-Zhenxiong, Qianxi-Dafang, Zhijing-Nayong, and Puding-Puan fault blocks. The distribution of these fault blocks is mapped for the first time. The unbalanced subsidence and uplifting among fault blocks caused the tilting of these fault blocks with one side elevated, which controlled the growth of biogenic reefs and the development of dolostones, finally leading to the formation of reef-controlled reservoirs. During the Late Permian, the Dabashang frontal fault block upwarped at its west end, downwarped at its east end, uplifted in the south side, and tilted to the north; while the Huayinshang and Dongbutaiyuan fault blocks upwarped at its north end, downwarped at its south end, elevated in the east side, and tilted to the west. It is therefore suggested that exploration of reef-controlled reservoirs should follow the following principles：paying attention to structural control of fault block on reservoirs; drilling order being from the upwarped end to the downwarped end and from the elevated side to the tiled side; and performing sedimentary facies analysis before drilling when neither growth of biogenic reef nor tilting of fault block is known.