火山岩发育区地震成像技术探讨

Seismic imaging technology in volcanic rock areas

随着油气勘探程度的不断提高,已陆续发现一些以火山岩和火山碎屑岩为储集层的油气田。但是,由于火山岩对地震信号屏蔽作用明显,地震波在不同层系、不同类型火山岩中的速度差异大,导致火山岩发育区的速度建模和成像极其困难。EP地区处于阳江—一统断裂带,资源潜力大,且发育大量构造圈闭,同时,该地区发育古近系及上覆地层的多期火山岩,以往处理成果中火山岩内幕成像不清晰,难以刻画火山岩相和准确评估火山岩对油气生、储、盖条件的影响。为此,针对火山岩多次波压制、火山岩下弱信号恢复、火山岩速度精细刻画等方面的关键问题开展新的处理技术探索。首先采用MWD(Model based Water-layer related Demultiple)技术预测火山岩多次波;然后利用AVO剩余振幅补偿和低频算子外推随机噪声衰减技术提高火山岩下弱信号质量;最后,联合应用初至波层析和反射波网格层析技术构建精确的叠前深度偏移速度模型。重处理后的叠前深度偏移成果显示,火山岩及下伏地层成像质量显著提高,表明所提重处理技术方案对提高火山岩发育区地震成像质量有较好的借鉴意义。

With the continuous improvement of oil and gas exploration,some oil and gas fields with volcanic rocks and volcaniclastic rocks as reservoirs have been discovered.However,due to the significant shielding ef⁃fect of volcanic rocks on seismic signals,the significant velocity variations of seismic waves in different layers and types of volcanic rocks,velocity modeling and imaging in volcanic rock development areas are extremely dif⁃ficult.The EP region is located in the Yangjiang⁃Yitong Fault Zone,with great resource potential and a large number of structural traps.Meanwhile,the Paleogene and its overlying strata have developed multiple periods and layers of volcanic rocks.Due to unclear imaging of the volcanic rocks and their underlying strata,it is diffi⁃cult to give a good definition of volcanic facies and to accurately evaluate the impact of volcanic rocks on the con⁃ditions of hydrocarbon generation,storage,and capping.This paper explores some new methods and new tech⁃nology attempted for key issues such as multiple wave suppression,weak signal recovery under volcanic rocks,and precise velocity modeling of volcanic rocks.Firstly,MWD(Model based Water-layer related Demultiple)technology is used to predict volcanic multiples.Then,AVO residual amplitude compensation and low⁃fre⁃quency operator extrapolation random noise attenuation techniques are used to improve the quality of weak sig⁃nals under volcanic rocks.Finally,first break tomography and grid⁃based tomography are used for accurate PSDM(Prestack Deep Migration)velocity modeling.The reprocessed PSDM results demonstrate substantial improvement in imaging of volcanic rocks and their underlying strata,indicating that the reprocessing techno⁃logy scheme can be a good reference for seismic imaging in volcanic rock areas.