利用Walkaway VSP技术预测川西北深层碳酸盐岩储层

Deep carbonate reservoir prediction in the Northwest Sichuan with Walkaway VSP data

四川盆地川西北龙门山冲断带下二叠统海相碳酸盐岩勘探潜力巨大,SYS地区主要目的层栖霞组发育一套孔隙型白云岩储层,该套储层埋藏深、厚度小、非均质性强,导致钻前预测误差大,储层预测难度大。为此,结合钻井、测井、井中地震和三维地震资料,提出了井地联合提高钻前预测精度的思路。通过初至拾取、三分量旋转和共炮集的中值滤波、保幅SVD滤波得到高信噪比的反射波记录,由VSP直接测得的下行波提取子波进行已知子波反褶积压制多次波,进一步提高分辨率;然后基于零井源距VSP资料约束进行Walkaway VSP速度建模;最后采用基于射线追踪共接收点归位和相干叠加成像方法得到Walkaway VSP成像。通过约束反演和属性分析开展储层横向预测,取得了良好的效果。

Lower Permian marine carbonate rocks in the Longmen Mountain thrust belt in the Northwest Sichuan Basin have good potential.However porous dolomite reservoirs in Qixia Formation,SYS Area are characterized by deep burial,thin-beds,and strong anisotropy,which bring huge difficulties in the reservoir prediction.To overcome the difficulties,we propose a joint use of drilling,logging,borehole seismic,and 3 Dseismic data to improve the pre-drilling prediction.High signal-to-noise ratio(SNR)data is obtained with a few processing tools such as firstbreak picking,3 Crotation,common-shot-gather median filtering,and amplitudepreserved SVD filtering.The wavelet is extracted from VSP down-going waves,and the wavelet deconvolution is performed for multiple removals to improve data resolution.After Walkaway VSP velocity modeling based on the zero offset VSP data,Walkaway-VSP imaging is obtained with raytracing mapping in the common receiver domain and coherent stacks.Finally the reservoir distribution prediction is carried out with the constrainedinversion and attribute analysis,and good results are achieved.