陕甘宁中生代地层异常压力对次生孔隙形成的作用

陕甘宁盆地三叠系延长统是国内外典型的低渗特低渗油田 ,储集层主要为三角洲砂体 ,压实作用和胶结作用强烈 ,储层非均质性非常严重 ,因此预测次生孔隙发育带是寻找油气聚集带的关键 .通过对陕甘宁盆地陇东地区延长统次生孔隙形成的主控因素分析 ,认为陕甘宁盆地延长统次生孔隙的形成除了受沉积有利相带控制外 ,还与地层异常压力的作用密切相关 .研究认为陇东地区异常压力的形成机理主要由于成岩过程中粘土矿物脱水作用 .粘土矿物大量脱水时间正好与有机质脱羧期相一致 ,从而在异常压力作用下将生油岩中的大量有机酸及 CO2 带到与之相邻的储集层中 ,并沿着有利储集相带运移 ,在酸性水经过的地方形成大量的次生孔隙 ,为后期油气运聚提供有利通道及宿住空间 ,从现今的勘探结果来看 ,通过研究地层异常压力纵横向分布特征 ,并结合有利相带研究预测次生孔隙育良带是行之有效的方法 .

Influence of the Abnormal Formation Pressure on the Forming of the Secondary Pore in Yanchang Series,Shanganning Basin

Yanchang series is a typical low permeability reservoir,and its favourable sandstone reservoir is delta facies.Heavy compaction,cementation and heterogeneity exist in it.According to the analysis of the main control factors of forming the secondary pore,it is held that the secondary pore in Longdong area is controlled by both favorable facies belt and abnormal formation pressure.It is also held that the formation of the abnormal formation pressure is due to the dewatering of the clay mineral during diagenesis because the dewatering time is identical with the decarboxylation time of organism.Organic acid and CO 2 are driven to adjacent favorable reservoirs under the abnormal formation pressure,and a lot of secondary pore is produced in the runners.From the present exploration result,it is useful to predicting the development of secondary pore to study the distribution of abnormal formation pressure.