洛带气田上侏罗统遂宁组沉积相及含气地震响应特征

Sedimentary facies and seismic responses in the Upper Jurassic Suining Formation,Luodai Gas Field

关键词:  洛带气田  上侏罗统  遂宁组  沉积相  地震响应  川西

Key words:  Luodai Gas Field  Upper Jurassic  Suining Formation  sedimentary facies  seismic response  western Sichuan

摘要:

洛带遂宁组气藏为新发现气藏,已提交天然气探明储量上百亿立方米。洛带遂宁组沉积环境以季节性浅水湖为主,发育进积型三角洲前缘亚相沉积,有利的沉积微相是三角洲前缘水下分流河道、河口砂坝和席状砂。物源来自川西坳陷西侧的龙门山,其中坳陷东坡的新都—洛带地区处于中部的砂泥岩互层的三角洲相带,在斜坡带上形成了大型的遂宁组岩性圈闭。洛带地区遂宁组具有多套储盖组合,又靠近下伏烃源岩,对天然气的富集和保存十分有利。通过合成记录的标定、Jason反演表明,遂宁组含气砂岩的地震响应模式为“强波谷、中—强波峰,低波阻抗”模式;砂泥互层型的地震响应是“强中弱”。该大型岩性气藏的发现,说明川西地区浅层气仍然具有大的勘探前景,遂宁组气藏将是浅层扩展评价勘探和风险勘探的重要目标。

Abstract:

The Suining Formation gas pools as newly-explored gas pools in Luodai have an explored reserve of more than 10¹⁰ m³ of natural gas. The sedimentary environments are dominated by ephemeral shallow lakes, where the prograded delta front subfacies deposits are developed. The favourable sedimentary microfacies consist of the delta front subaqueous distributary channel, channel-mouth bar and sheet sands. The clastics are predominantly derived from the Longmen Mountains west of the western Sichuan depression. The Xindu-Luodai zone on the eastern slope of the depression is occupied by the delta facies with the intercalations of sandstone and mudstone, in which a number of Suining Formation lithologic traps are developed. Several sets of reservoir-seal associations near the underlying source rocks facilitate the accumulation and preservation of natural gas. The integration of synthetic well logs and Jason inversion shows that the seismic responses of the Suining Formation gas-bearing sandstones are manifested by the model of " strong wave trough, moderate-strong wave crest and low wave impedance". The discovery of these large-sized lithologic gas pools opened up a vast range of prospects for the shallow gas exploration in western Sichuan.The Suining Formation gas pools will serve as the key target of extended assessment and risk exploration of the shallow gas in the study area.