碳酸盐岩异常地层压力成因不同于碎屑沉积岩的欠压实机制，其纵波速度-孔隙度关系分散，采用常规方法进行碳酸盐岩地层压力预测具有很大的不确定性。基于等效介质理论，计算不同孔隙结构碳酸盐岩的纵波速度，在此基础上，分析孔隙结构导致的常规地层压力预测方法的预测偏差。结果表明：在应力状态、矿物组成和孔隙度相同条件下，裂隙类孔隙使地层压力预测结果偏高，易造成井漏、储层污染等问题；溶孔类孔隙使地层压力预测结果偏低，易诱发溢流、井涌等复杂情况；当裂缝、溶孔共存时，地层压力预测偏差的正负不仅受裂隙与溶孔相对体积比的影响，也受其绝对体积含量的控制；对于复杂孔隙结构碳酸盐岩，油气钻井工程中采用常规的地层压力预测方法和井身结构设计系数存在较大的安全隐患。%The origin of abnormal pore pressure in carbonate rocks is different from that of clastic sedimentary rocks. P-wave velocity and porosity have poor correlation in carbonate rocks, which results in high uncertainty in pore-pressure prediction u-sing common methods. Based on the effective media theory, the P-wave velocity in carbonates with different types of pore structure was calculated, and then the deviation of pore-pressure predicted with conventional methods was analyzed. The re-sults show that under the same stress condition, mineral composition and porosity, the pore-pressure of carbonate formation with crack type porosity tends to be over-estimated, which can cause lost circulation and reservoir damage during drilling. On the other hand, the pore-pressure of carbonate formation with moldic or vug type porosity can be under-estimated, which may lead to well kick or even blowout. For carbonate formations with both crack and moldic types of porosity, whether the predic-ted pore pressure is under-or over-estimated depends not only on the relative volume fraction of cracks and vugs, but also on their absolute volumes. Therefore, there are safety concerns when conventional pore-pressure prediction method and casing program design method are used during drilling carbonates with complicated pore structure.
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