纵波速度方位各向异性在页岩气裂缝预测中的应用

Azimuthal Anisotropy of Velocity of Longitudinal Wave Applied to predicting Shale Gas Fractures

在页岩气勘探开发中,裂缝直接影响页岩气的保存和渗流能力,裂缝的有效预测对水平井轨迹设计和后期压裂施工具有重要指导意义。在HTI介质中纵波NMO速度随观测方位角呈椭圆分布,依此理论,对工区叠前CMP道集进行方位角道集的划分与预处理,在处理好的分方位角道集上提取目的层NMO速度,对速度点进行平面最小二乘法椭圆拟合,依据椭圆特征对工区的裂缝密度与方向进行了预测,预测结果与成像测井有较高的吻合度,证明了利用纵波速度方位各向异性进行页岩裂缝预测方法的适用性与可靠性。

In exploration and development of shale gas, fractures have a direct impact on conservation and filtration capability of shale gas. Effective prediction of fractures is significant in horizontal well trajectory design and late fracturing construction. Based on the theory that NMO velocity of longitudinal wave presents elliptical distribution along with observed azimuth in HTI medium, this paper divides and pretreats azimuth gather for prestack CMP gather in the workzone, collects target--layer NMO velocity from disposed sub--azimuth gather, tries on ellipse fitting of the speed point through flat least square method, and then predicts fracture density and direction according to elliptic characters. Prediction result is greatly consistent with imaging logging, proving that azimuthal anisotropy of velocity of longitudinal wave is suitable and reliable for predicting shale fractures.