碳酸盐岩弹性波特性的应力敏感性定量描述及地层压力预测模型研究

There are abundant oil and gas resources reserved in carbonate rocks. But the velocity-effective stress curve of carbonate rock is very flat, so there is very little velocity sensitivity to the change of effective stress, which greatly increases the uncertainty in pore pressure predictions and restricts the exploration and production efficiency of carbonate reservoirs worldwide. The development of rock physics models with strong stress-dependence can improve the reliability of the pore pressure predictions in carbonate rocks. This program will systematically study the stress dependence of elastic wave properties of carbonate rocks by experiments and numerical modeling. Based on the synthetic carbonate samples with special pore structures and carbonate outcrops with representative depositional facies and diagenesis, the stress dependence of elastic wave properties of carbonate samples with different pore structure will be quantitatively evaluated by experiments. A dynamic numerical modeling method of elastic wave propagation in porous media during the loading/unloading process will be built. And then the pore structure deformation and elastic wave propagation in carbonate rocks with different pore structures in the loading/unloading process will be modeled by this dynamic modeling method. Combining the experiments and numerical modeling results, rock physics models quantitatively describing the variations of elastic wave velocity, attenuation factor, and dynamic moduli with effective stress for carbonate rocks are developed, respectively. Based on the above study, rock physics models of the integrated parameter with strong stress dependence for scenarios of different pore structures and pore fluids are built according to the principles of electrical signal amplification and fidelity. Moreover, the inversion of pore structure parameters of carbonates will be achieved by time-frequency analysis and nonlinear methods using array acoustic logging data. Finally, a pore pressure prediction model for carbonates considering the influence of pore structure is built, which would enhance the efficiency of exploration and development in carbonate oil and gas reservoirs.

碳酸盐岩中油气资源丰富，但其速度-有效应力曲线平缓、梯度小，地层压力预测的不确定性大，制约碳酸盐岩油气藏的有效勘探开发。建立强应力敏感性的岩石物理模型可提高碳酸盐岩地层压力预测的可靠性。本项目拟采用实验和数值模拟相结合的方法，系统研究碳酸盐岩弹性波特性的应力敏感性。通过制备特殊孔隙结构的人造岩心、典型沉积相与成岩作用组合的露头岩心，对不同孔隙结构碳酸盐岩的弹性波应力敏感性进行实验研究；建立加/卸载过程中弹性波在多孔介质中传播的数值模拟方法，模拟加/卸载过程中碳酸盐岩的孔隙结构动态变形及弹性波传播特性；综合实验和数值模拟结果，分别建立碳酸盐岩弹性波速度、衰减系数、动态弹性参数-有效应力模型。在此基础上，针对不同的孔隙结构和孔隙流体组合，基于信号保真放大原理，建立强应力敏感性的复合参数-有效应力模型，并研究碳酸盐岩孔隙结构参数反演方法，建立考虑孔隙结构的碳酸盐岩地层压力预测模型。

碳酸盐岩孔隙结构复杂，其速度-孔隙度关系分散、速度-有效应力曲线梯度小，不符合常规地层压力预测模型的应用假设，地层压力预测的不确定性大、钻探风险高。碳酸盐岩地层压力预测难题是制约其有效勘探开发的关键。为提高碳酸盐岩地层压力预测的可靠性，本项目采用实验和数值模拟相结合的方法，系统研究了复杂孔隙结构碳酸盐岩弹性波特性的应力敏感性，并在此基础上构建了考虑孔隙结构的碳酸盐岩地层压力预测模型。在实验方面，采用人造岩心、野外露头、井下岩心测量了不同围压下的纵横波速度，结合岩心的孔隙结构特征，从速度-有效应力关系、纵横波速比、归一化速度等方面定量分析了碳酸盐岩的应力敏感性，发现了碳酸盐岩纵横波速比随有效应力的异常变化特征。考虑频率和尺度效应，制备了不同孔隙结构碳酸盐岩的井筒物理模型，并分析了孔隙结构对测井声波的影响规律。在数值模拟方面，构建了弹性波在复杂孔隙结构多孔介质中传播的跨频段数值模拟方法，采用流固耦合的动态数值模拟方法，模拟计算了不同孔隙结构碳酸盐岩在加载过程中的孔隙变形和弹性波传播。综合实验和数值模拟结构，建立了复杂孔隙结构碳酸盐岩的速度-有效应力模型。同时，基于测井数据建立了“定性识别-分级评价-智能预测”的多层次裂缝预测模型，并采用塔里木油田顺北一区、华北奥陶系碳酸盐岩层测井数据进行了试算与验证。在此基础上，建立了考虑孔隙结构的碳酸盐岩地层压力预测模型，并采用川东北普光气田、塔里木顺北一区的碳酸盐岩层工程数据进行了计算分析，验证了模型的可靠性。该项目研究成果有效提升了碳酸盐岩地层压力预测的可靠性，也能为裂缝性地层钻井防漏堵漏提供有效指导，提高了碳酸盐岩油气藏的钻探开发效率。