异常地层压力声波衰减分析及地层压力地震数据外推反演

澳大利亚西北大陆架卡拉汶盆地含有丰富的油气资源, 但其地质条件复杂, 普遍存在异常地层高压分布,特别是该区区域盖层-中深层巨厚的Muderong页岩层内存在局部异常高压带,给石油钻井带来巨大困难.本文根据卡拉汶盆地北部地区10余口井的实测地层压力资料、声波测井数据和联井地震剖面, 研究该页岩层内异常压力千赫兹尺度声波响应的衰减特征,及其与地层有效压力之间的关联计算模型.通过联井地震数据的井-震相关性分析进行井-震过渡,研究井旁地震数据在异常高压带的衰减特征,及其与地层有效压力之间的关联计算模型,从而实现井震资料联合进行地层压力地震外推反演.研究表明,Muderong页岩层地层有效压力与井中声波速度/阻抗品质因子和井旁地震阻抗品质因子具有良好的正向相关性,根据二者交汇数据拟合经验公式反算得到的各井有效压力结果基本反映出实测有效压力曲线的变化特征.卡拉汶盆地北部地区地震数据具有良好的井-震相关性,地震资料品质相对可靠,确保了声-压相关分析的井-震过渡.最后,通过地震阻抗品质因子与地层有效压力之间的关联计算模型,进行该区异常地层压力地震外推反演,预测结果与钻井证实的异常压力分布特征基本符合.本研究为卡拉汶盆地中深部区域盖层局部异常高压带的地层压力外推反演提供了一种有效途径.

Acoustic wave attenuation analysis of the abnormal geo-pressure and seismic extrapolation inversion of the formation pressure

The Carnarvon Basin in the North West Shelf of Australia is rich in hydrocarbon resources, but the geological conditions are very complex, and abnormal formation pressure is ubiquitous; especially local abnormal high pressure zones exist in the middle-deep massive heavy Muderong Shale, which brought great difficulties to the oil drilling. This paper chooses the regional caprock Muderong Shale in the northern Carnarvon Basin as a test target, based on the measured formation pressure data, acoustic logging data, and cross-well seismic data, studies the abnormal geo-pressure and the attenuation characteristics of kHz-scale acoustic response, and the relevant calculation model between attenuation parameter and formation pressure, so as to transit from seismic-to-well correlation analysis of the seismic data in the area to the sensitivity analysis of the abnormal geopressure with the attenuation parameter of borehole-side seismic data and the relevant model building, thus the seismic extrapolation inversion of formation pressure can be achieved. The result of acoustic logging data shows that there is a good positive correlation between the effective pressure and the acoustic velocity/impedance quality factor, and based on the fitting polynomial formulas obtained from the crossplot of the two, the back-calculated effective pressure curve can reflect the variation characteristics of the measured effective pressure well. Then the result of the cross-correlation analysis and correlation coefficients between the filtered impedance logs and the borehole-side seismic relative impedance shows that the seismic data in the Northern Carnarvon Basin has an approved seismic-to-well correlation, so the seismic data quality is relatively reliable, ensuring seismic-to-well transition of sound -pressure correlation analysis. Finally, based on the correlation analysis of the borehole-side seismic absolute impedance and the effective pressure, we build the seismic extrapolation inversion model of formation pressure, and predict the effective pressure of one cross-well seismic line, the result is basically consistent with the measured pressure and characteristics of pressure distribution in the area. So this paper provides an excellent way to the seismic prediction about local abnormal pressure zones in the Muderong Shale in the northern Carnarvon Basin.