膏盐岩对异常高压形成与分布的控制--以柴达木盆地狮子沟地区为例

异常高压在一定程度上影响和控制油气藏的分布,膏盐岩的发育与异常高压的分布存在明显的对应关系。通过对柴达木盆地狮子沟地区膏盐岩发育特征的详细研究,结合实测和计算地层压力资料对该区地层压力分布规律进行分析,探讨膏盐岩和地层压力的关系。研究表明,狮子沟地区膏盐岩纵向上具有四种沉积序列,横向上与砂岩呈“此消彼长”的关系,与泥岩呈“同增同涨”的关系。该区地层压力纵向上表现出分段特征:常压段、增压段和强压段。这种分段性在膏盐岩不发育的区域没有发现。狮子沟地区异常高压横向范围覆盖了膏盐岩的发育范围,地层压力系数随着膏盐岩厚度的变薄而减小。因此,膏盐岩对异常高压的分布具有明显的控制作用,其沉积脱水、致密性、塑性、流动性、高热导率等性质是促使异常高压形成的根本原因。

The Control Effect of Gypsum-salt Rocks on Formation and Distribution of Overpressure: A case of Shizigou area,Qaidam Basin

Overpressure influence and control of oil and gas reservoir distribution, there is obvious relationship between overpressure distribution and development of gypsum-salt rocks. Study on the development of gypsum-salt rocks in Shizigou area, analysis of regularity of distribution of formation pressure with actual and computational data to the area, for discussing the relationship between gypsum-salt rocks and formation pressure. Gypsum-salt rocks have four sedimentary sequences in the vertical, they were inversely proportional relationship with sandstone, and were proportional relationship with mudstone in the lateral. The formation pressure has the feature of segmentation in the vertical: Ordinary pressure section, pressure coefficient range in 0.9~1.2, it's in up-salt zone; Boost pressure section, pressure coefficient range in 1.3~1.8, it's in inter-salt zone; Excess pressure section, pressure coefficient above 1.8, it's in pre-salt zone. The undeveloped area of gypsum-salt rocks have no this kind of segmentation. Pressure range covered the development range of gypsum-salt rocks. Overpressure decreased as gypsum-salt rocks thickness thinning. Gypsum-salt rocks have obvious control effect for overpressure distribution. Dewatering, compactness, plasticity, flowability, and high thermal conductivity of gypsum-salt rocks are the root cause of formation of overpressure.