川东北五宝场地区须五段致密砂岩叠前储层预测

Pre-stack reservoir prediction of tight sandstone of the fifth member of Xujiahe Formation in the Wubaochang area of northeastern Sichuan

摘要:

川东北五宝场地区须家河组须五段具有特低孔特低渗致密砂岩储层特征，常规叠后纵波阻抗难以区分泥岩背景下的储层，储层预测和含气性检测难度大。本文基于Gassmann方程进行流体替换并对工区缺失横波资料的井进行横波预测，并分别正演饱含不同流体性质的道集。研究发现储层饱含水为一类AVO响应特征，储层饱含气为二类AVO特征，AVO规律明显，进而采用实钻井的样本点建立岩石物理模板，选取纵横波速度比联合纵波阻抗圈定致密砂岩储层，利用更低的纵横波速度比能有效指示含气性。结果表明：砂体及储层展布规律能够得到很好的表征，叠前含气性预测对井吻合率达到90.9%。叠前预测在川东北五宝场地区须家河组须五段致密砂岩含气性识别中是有效的，有助于提高钻探成功率与开发效益。

Abstract:

The tight sandstone reservoir of the fifth member of Xujiahe Formation in the Wubaochang area of northeastern Sichuan is characterized by ultra-low porosity and ultra-low permeability. Conventional post-stack P-wave impedance is inefficient to distinguish reservoir interbedded in mudstone, which makes it difficult to perform reservoir prediction and gas-bearing detection. This work conducted fluid replacement based on the Gassmann equation, predicted shear waves for wells lacking shear wave data, and forwarded gathers saturated with different fluid properties in the study area. Results show that the reservoir saturated with water displays AVO type-I response, and that saturated with gas shows AVO type-II response, indicative of regular AVO features. A petrophysical template was established by using sample points of actual drillholes, the Vp/Vs, and P-wave impedence were selected to delineate tight sandstone reservoir. Small Vp/Vs ratios are indicated to effectively indicate the gas-bearing properties. Results show that the distribution law of sandstone and reservoir can be well characterized, and the pre-stack gas-bearing prediction matches the well at a rate of 90.9%. Pre-stack prediction is inferred to be effective in identifying gas-bearing properties of tight sandstones in the fifth member of Xujiahe Formation in the Wubaochang area of northeastern Sichuan, which will help to improve drilling success rate and development benefits.