基于叠前同时反演的致密砂岩储层预测及含气性识别--以苏里格S区块为例

Prediction and identification of gas-bearing properties of tight sandstone reservoirs through simultaneous pre-stack inversion:A case study of block S in Sulige gas field

苏里格S区块储层与围岩阻抗差异小、气水关系复杂,叠后纵波阻抗反演方法难以区分优质储层,通过研究区岩石物理分析可知,叠前参数纵横波比可以有效区分岩性和含气性。本文首先进行模型正演确定储层地震响应特征;然后通过适用于砂泥岩的Xu-White模型进行岩石物理建模及横波预测,建立岩石物理模板;其次采取线性去噪、剩余振幅补偿等处理方法对CRP道集进行优化;最后通过叠前同时反演定量预测储层厚度及含气性。结果表明:①储层顶界的地震反射特征为强波谷反射,底界反射不明显;②纵横波比小于1.68可有效划分砂岩,联合纵波阻抗小于12200 g·cm^(-3)·m·s^(-1)预测储层,再由更低的纵横波比小于1.57识别含气性;③储层展布特征与含气性预测范围趋势相似,但在局部上存在差异,储层发育程度与其含气性不一定呈正相关。本文所提方法期望为下一步圈定有利含气储层面积及井位部署提供有力的技术支撑。

Owing to the small impedance difference with surrounding rock and complex gas-water relationships,it is difficult to identify high-quality reservoirs in block S in the Sulige gas field through the post-stack P-wave impedance inversion.According to the petrophysical analysis of the study area,the pre-stack parameter v_(p)/v_(s) ratio can be used to effectively identify lithology and gas-bearing properties.This study firstly determined the seismic response characteristics of the reservoirs through forward modeling.Secondly,it conducted petrophysical modeling and the prediction of shear-wave velocities using the Xu-White model suitable for sandstone and mudstone and accordingly established a petrophysical model.Thirdly,the CRP gathers were optimized using the processing methods such as linear denoising and residual amplitude compensation.Finally,the thickness and gas-bearing properties of the reservoirs in block S in the Sulige gas field were quantitatively predicted through simultaneous pre-stack inversion.The results are as follows.(1)The top boundary of the reservoirs in the study area shows the seismic reflection characterized by strong trough reflection,while the bottom boundary of the reservoirs shows unapparent seismic reflection;(2)The v p/v s ratio of less than 1.68 can be used to effectively determine sandstone.This combined with the P-wave impedance of less than 12200 g·cm^(-3)·m·s^(-1) can be used to predict the reservoirs in the study area.Moreover,a v_(p)/v_(s) of less than 1.57 can be used to identify the gas-bearing properties;(3)Reservoir distribution and the predicted gas-bearing range have similar trends but differ locally.The development degree of reservoirs is not necessarily positively correlated with the gas content.The method proposed in this paper is expected to provide strong technical support for delineating the favorable gas-bearing reservoir area and deploying well locations in the future.