A Pore Pressure Calculating Method for Carbonate Formations Based on Fluid Velocity
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摘要: 碳酸盐岩地层具有非均质性强、孔洞与裂缝发育和岩石骨架刚度较强的特点，以正常压实理论为基础建立的地层孔隙压力求取方法不适用于碳酸盐岩地层，为此，进行了碳酸盐岩地层孔隙压力求取方法的研究。碳酸盐岩岩样声速试验和理论分析发现，不同孔隙压力下的碳酸盐岩纵波速度变化主要是由孔隙流体纵波速度变化引起的。利用小波变换法提取和放大孔隙流体纵波速度小幅波动对岩石纵波速度的影响关系，确定碳酸盐岩地层的异常压力层，并与实测地层孔隙压力数据相结合，建立了碳酸盐岩地层孔隙压力预测模型，形成了基于流体声速的碳酸盐岩地层孔隙压力预测方法。应用实例表明，基于流体声速的碳酸盐岩地层孔隙压力预测方法可以预测碳酸盐岩地层的孔隙压力，误差小于15%，满足工程要求，为碳酸盐岩地层孔隙压力预测提供了一种新方法。Abstract: Compared with clastic sandstone formations,carbonate formations exhibit more pronounced heterogeneity,with more developed pores and fractures and higher matrix rigidity.Therefore,the formation pore pressure calculation method based on the normal compaction theory is unsuitable for carbonate formations.In this paper,the method for calculating the pore pressure of carbonate formation was studied.It was indicated from acoustic velocity experiments and a theoretical analysis on carbonate rock samples that the change of P-wave velocity in carbonate rocks under different pore pressure was mainly caused by the change of P-wave velocity in pore fluids.The effect of small fluctuation of P-wave velocity in pore fluids on P-wave velocity in rocks was extracted and amplified by means of wavelet analysis method to identify the abnormal pressure layers in carbonate formations.Then,combined with the measured formation pore pressure,the characteristic parameters reflecting pressure were searched for and a model for predicting the pore pressure of carbonate formation was established.And thus a pore pressure prediction method of carbonate formation based on fluid velocity was developed.It was indicated from application cases that this method could predict the pore pressure of carbonate formations with a margin of error lower than 15%,which satisfies engineering requirements.It also provides a new method for predicting the pore pressure of carbonate formation.
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Keywords:
- carbonate rock /
- pore pressure /
- fluid velocity /
- wavelet analysis method
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