| Mahu Sag on the northwest edge of the Junggar Basin is one of the key areas for onshore shale oil exploration in China.The shale oil in this area is mainly distributed in the Fengcheng Formation of Mabei,with a burial depth of more than 4500m.It shows a favorable exploration area of 840km~2 and large thickness(over 100 meters),with great resource potential,and is the main successor field for future exploration and development of Xinjiang Oilfield.However,shale rock owns various minerals in the region,with low porosity and ultra-low permeability reservoirs,overall development of fractures,local enrichment,and significant lateral changes in lithology,reservoir space properties,and hydrocarbone content.Efficient exploration and development of shale oil requires the existence of enriched areas for shale oil,followed by effective fracturing and transformation of shale reservoirs.The former is manifested as the geological"sweet spot"of shale,while the latter is manifested as the engineering"sweet spot"of shale.The prediction of the dual"sweet spots"of geological engineering is the foundation of shale oil efficiency development,and accurate prediction of the sweet spot development area of geological engineering is a key part of shale oil well deployment and hydraulic fracturing design optimization.This paper is based on high-density and wide-azimuth 3D seismic data to conduct seismic prediction for key parameters of geological engineering double"sweet spot"in Mabei shale reservoirs,in order to clarify the lateral distribution characteristics of sweet spots and provide a basis for the deployment demonstration and hydraulic fracturing design of shale oil horizontal wells.1)Improving the signal-to-noise ratio and resolution of deep seismic data:We have proposed a 3D seismic Kalman filtering method combined horizontally and vertically,and improved the spot spectrum whitening frequency raising method,achieving interpretive optimization of seismic data targets,providing high signal-to-noise ratio and high-resolution data volume for subsequent prestack inversion and fracture prediction;2)Improving the prediction accuracy of seismic elastic parameters:Starting from the problems of poor stability of traditional three-parameter and more AVA inversion equations and accumulated errors in multiple indirect combination calculations,we have developed a three step two-parameter seismic integrated prestack inversion method for key parameters of shale oil geological engineering sweet spot;3)Improved the accuracy and efficiency of prestack azimuth nature fracture prediction:We improved the azimuthal elliptical equation containing fracture strength and azimuth,and proposed a trace operation ellipse fitting prestack azimuth prediction method.In summary,this paper establishes a three-step,two-parameter seismic inversion method,which effectively solves the problem of the traditional three-parameter AVA inversion in which the P-wave reflection coefficient is not sensitive to density parameter,the stability of deep multi-parameter(more than three parameters)inversion equations is poor,the inversion accuracy is low,and the indirect combination of seismic elastic parameters inevitably leads to cumulative errors.Previous geological and engineering key parameters for sweet spot were predicted separately,without achieving integrated design and inversion result with low calculation efficiency and poor targeting.Finally,this paper has improved the prediction accuracy of reservoir parameters,brittleness,horizontal stress difference ratio,and fracture fluid factor.Combined with post stack coherence,curvature,and trace operation azimuth amplitude ellipse fitting fracture prediction results,the integrated seismic prediction and application for geological engineering sweet spot of Mahu shale oil in the Junggar Basin have been realized,which supports the well location deployment,directional well trajectory optimization and benefit development area effectively. |
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