转换波叠后联合反演技术在川西须家河组气藏的应用

Application of converted-wave poststack joint inversion in the Xujiahe Formation gas reservoir in the western Sichuan Basin

川西坳陷上三叠统须家河组气藏为超致密超高压非常规近源气藏,具有地质条件复杂、成藏机理不清、地震资料有效频带窄与主频低等不利因素,勘探开发难度极大。常规纵波反演技术不能够充分地利用横波信息,无法提供与储层预测、含气性识别等相关的精确参数,难以有效地解决致密气藏的勘探难题。而转换波叠后联合反演技术同时利用全波测井、地震、地质等综合信息,反演出泊松比、纵横波速度比、纵横波阻抗、密度等与岩性和物性相关的重要参数,为致密油气藏的描述提供了更准确、有效的依据。进行转换波叠后联合反演之前,还需要对PP波与PS波进行匹配处理,消除反射波组的频率、相位、波形等差异,以建立准确的反演初始模型。将该技术应用到川西新场地区须家河组气藏描述,获得了良好的储层预测、岩性识别及含气性检测效果。

The Upper Triassic Xujiahe Formation gas reservoirs in the deep West Sichuan Depression are non-conventional near-source gas reservoirs featured by super tightness and super-high pressure.Gas exploration and development are extremely challenging due to the complex geologic conditions,unclear hydrocarbon accumulation mechanism,narrow effective frequency band and low dominant frequency.The conventional P-wave inversion technique cannot fully utilize the S-wave information,cannot provide accurate parameters for reservoir prediction and gas potential identification,thus cannot effectively solve the problem of tight gas reservoir exploration.In contrast,the converted-wave poststack joint inversion technique can simultaneously utilize full-wave log,seismic and geologic data to abstract some key parameters that are associated with lithology and physical property,such as the Poisson's ratio,PP-to PS-wave velocity ratio,PP-and PS-wave impedance and density.These parameters provide more accurate and effective information for the description of tight reservoirs.Before the converted-wave poststack joint inversion,the matching of PP-and PS-wave should be performed to eliminate the differences of reflected wave groups in aspects of frequency,phase and waveform,so as to build a precise initial inversion model.This technique has been successfully applied to the description of the Xujiahe Formation gas reservoirs in Xinchang area of the western Sichuan Basin.The results of reservoir prediction,lithology identification and gas potential detection are satisfactory.