深水浅层松散沉积物水合物赋存状态识别与饱和度计算

Hydrate occurrence identification of shallow loose sediments in deep water and its saturation calculation

中国海域深水浅层天然气水合物资源量巨大。海域深水浅层地质疏松,天然气水合物储层无致密盖层、非均质性较强,天然气水合物赋存状态难以识别,极大地制约了天然气水合物饱和度的预测工作。基于海域深水浅层天然气水合物的声、电响应特征,利用电阻率和纵波速度交会图版法识别天然气水合物的赋存状态,采用含泥质修正的密度公式计算天然气水合物储层孔隙度。采用含泥质修正的电阻率法、等效介质法和寻找最小联合误差的声电联合反演法预测QDN盆地YL靶区天然气水合物饱和度。预测结果表明,QDN盆地YL靶区采用联合反演法的预测值与氯离子浓度法的实测值最吻合,联合反演法预测误差为0.09%~14.89%,平均误差为6.85%。表明在判断水合物赋存状态的基础上选择相应的声电联合反演饱和度计算模型能极大地提高水合物饱和度的精度,为水合物饱和度的计算提供了一条好的途径。

The Chinese offshore area holds vast reserves of deepwater and shallow gas hydrates.Due to the geo⁃logical looseness of the deepwater and shallow layers in the offshore area,as well as the absence of tight sealing layers and high heterogeneity in gas hydrate reservoirs,identifying the occurrence state of gas hydrates is chal⁃lenging,greatly impeding the prediction of gas hydrate saturation.Based on the acoustic-electric response char⁃acteristics of deepwater and shallow gas hydrates,the intersection method of resistivity and longitudinal wave velocity diagrams is employed to identify the occurrence state of gas hydrates.The pore volume of gas hydrate reservoirs is calculated using a density formula corrected for mud content.The prediction of gas hydrate satura⁃tion in the YL target area of the QDN Basin is conducted using the mud-corrected resistivity method,equivalent medium method,and joint inversion method finding the minimum combined error of acoustic and electric data.The results indicate that the predicted values using the joint inversion method in the YL target area of the QDN Basin are closest to the measured values obtained using the chloride ion concentration method,with prediction errors ranging from 0.09%to 14.89%and an average error of 6.85%.This suggests that selecting the appropri⁃ate acoustic-electric joint inversion saturation calculation model based on the determination of hydrate occur⁃rence states can significantly improve the accuracy of hydrate saturation prediction,providing a good approach for calculating hydrate saturation.