四川盆地元坝地区大安寨段页岩气“甜点”地震预测

页岩储层的埋深、厚度、有机碳含量、脆性、裂缝发育带等是评价页岩气"甜点"的主要地质指标。为此,以四川盆地元坝地区下侏罗统大安寨段二亚段为研究对象,根据页岩气地质评价标准,在地震资料特殊处理及多种资料综合分析的基础上,提出了一套页岩气"甜点"的地震预测技术。首先,通过合成记录精细标定页岩储层位置,确定优质泥页岩的测井及地震响应特征,结合地震相分析,落实泥页岩的宏观展布;然后,利用地震波阻抗反演和GR反演技术去"灰、砂找泥",在有机碳含量等敏感参数统计分析的基础上,通过铀曲线反演技术进行页岩储层有机碳含量及优质泥页岩厚度的定量预测;再利用裂缝预测技术预测优质页岩储层高产富集区;最后利用叠前纵、横波阻抗联合反演技术预测高脆性指数发育区,开展优质页岩储层压裂品质区的预测。通过以上地震预测技术,落实了元坝地区大安寨段二亚段页岩气"甜点"的勘探区域,为优化页岩气定向水平钻井和储层压裂改造的部署提供了依据。

Seismic prediction of sweet spots in the Da′anzhai Shale Play,Yuanba area,Sichuan Basin

Burial depth, thickness, total organic carbon (TOC) content, brittleness and fracture development of shale reservoirs are the major geologic criteria for the identification of sweet spots of shale gas plays. Taking the 2^nd interval of Da′anzhai Shale of the Lower Jurassic as the object of study, a set of seismic prediction technologies of sweet spots were developed based on special processing of seismic data and comprehensive analysis of various data based on these geologic criteria. First, logging and seismic responses of high quality shales were defined through fine calibration of shale reservoir location with seismogram and were analyzed in combination with seismic facies to determine the macroscopic distribution of the shales. Then, seismic impedance inversion and GR inversion technologies were used to identify shales from limestones and sandstones. Based on the statistical analysis of sensitive parameters such as TOC, the uranium log inversion technology was used to quantitatively predict TOC of a shale reservoir and the thickness of a high quality shale reservoir. After that, fracture identification was performed to predict play fairways. Finally, the pre stack joint P and S wave impedance inversion technology was used to identify shales with high brittleness suitable for hydraulic fracturing. These seismic prediction technologies of sweet spots were successfully applied to the 2^nd interval of the Da′anzhai Shale Play in the Yuanba area and the results provided a sound basis for the optimization of horizontal drilling and hydraulic fracturing operations.