厚层盖层段断层垂向封闭性定量评价方法及其应用

Quantitative evaluation method and its application for vertical fault seal of thick caprock intervals

断层和裂缝是导致油气垂向调整运移或散失(圈闭失利)的首要因素,但不同类型盖层段断层的垂向封闭性控制因素存在明显差异,制约着断层垂向封闭性评价。以厚层膏岩、泥岩盖层为研究对象,结合野外观察、岩石力学测试和室内油气藏解剖,建立了基于拜尔利摩擦定律、莫尔-库伦破裂准则和盖茨准则的盖层脆韧性转化量化评价方法,揭示出不同脆韧性盖层段断裂带内部结构的差异性,构建了不同盖层脆韧性条件下的断层垂向封闭性评价方法。结果表明:厚层膏岩、泥岩盖层段断层的垂向封闭性主控因素是盖层的脆韧性、断层在盖层段的变形机制及垂向封闭能力;采用断接厚度(HCJT)法量化表征准南地区安集海河组脆性域泥岩盖层段断层的垂向封闭性,其HCJT临界值约为400 m;采用泥岩涂抹系数(CSSF)量化表征库车坳陷东秋背斜南翼脆韧性域膏岩盖层段断层的垂向封闭性,其CSSF临界值为3.5~4.0。研究成果对中国沉积盆地断块油气藏三维立体勘探具有重要的指导意义。

Faults and fractures are primary factors that lead to vertical adjustment migration or leakage of oil and gas(trap failure),but controlling factors of vertical fault seal of different types of caprock intervals are obviously different,restricting evaluation of vertical fault seal.Taking thick gypsum caprock and mudstone caprock as study object,and combining with field observation,rock mechanics test and laboratory reservoir analysis,a quantitative evaluation method for caprock brittle-ductile transition is established based on Byerlee friction law,Mohr-Coulomb fracture criterion and Goetze’s criterion,revealing the difference of internal structure of fault zones in different brittle/ductile caprock intervals and constructing an evaluation method for vertical fault seal in different brittle/ductile caprocks.The results show that the main controlling factors of vertical fault seal in thick gypsum and mudstone caprock intervals are caprock brittleness/ductility,deformation mechanism of fault in caprock intervals and vertical sealing capacity.Vertical fault seal of mudstone caprock in brittle area of Anjihaihe Formation in Zhunnan area is quantitatively characterized by fault juxtaposition thickness(HCJT)method,with HCJT critical value of about 400 m.Vertical fault seal of gypsum caprock in brittle/ductile area of southern flank of Dongqiu anticline in Kuqa Depression is quantitatively characterized by shale smear factor(CSSF),with critical value of 3.5~4.0.The research provides important guidance for three-dimensional stereoscopic exploration of fault-block reservoirs in sedimentary basins in China.