纵波速度在碳酸盐岩地层压力评价中的方法探讨

DISCUSSING ON P- WAVE VELOCITY IN POREPRESSURE EVALUATION METHOD IN CARBONATE FORMATION

准确解释地层压力是钻井工程的基础。碳酸盐岩纵波速度变化不明显,在异常高压地层仅存小幅波动。基于Biot理论,建立了由岩石骨架和孔隙流体两部分组成的纵波速度方程。研究表明,纵波速度的小幅波动由地层压力变化引起,可用孔隙流体对纵波速度的贡献部分表征。利用小波变换方法对纵波速度进行分解,提取高频系数及孔隙流体对纵波速度的贡献部分,识别异常高压地层和建立地层压力评价模型。利用该方法对川东北地区碳酸盐岩地层压力进行了评价,并与实测值进行对比,证实该方法是可行的。

Accurately pore pressure prediction is the basic of drilling engineering. The P- wave velocity of carbonate rocks has insensitivity to pore pressure change,only has a small-scale fluctuation in abnormal high pressure formation. The P-wave velocity equation which consists of the pore fluid and the rock framework was established based on the Biot's theory. The study found that the contribution of pore fluid to P- wave velocity could be depicted as a small- scale fluctuation in P- wave velocity induced by changes of pore pressure. According to wavelet transform theory,P- wave velocity was decomposed,the high frequency coefficient and contribution from pore fluid to P- wave velocity were given. It makes it possible to identify abnormal pressure formation and establish the pore pressure evaluation model in carbonate rocks. This new method presented in this paper was applied to evaluate the carbonate formation pressure in Northeast Sichuan block,and compared with measured value,the results verified the method was feasible.