基于小平滑面的非线性网格层析速度建模技术--以四川盆地双鱼石区块为例

Nonlinear grid tomography velocity modeling technology based on small smooth plane and its application:An example from Shuangyushi block,Sichuan Basin

随着四川盆地西北部地区双鱼石区块勘探开发进程,钻井工程逐渐由早期勘探期直井向开发期大斜度水平井转变。但由于双鱼石区块地表、地下构造特征"双复杂"的情况,叠前时间偏移成像资料存在构造形态落实不准确,钻井揭示地层构造轴线和叠前时间偏移成果存在较大偏差。应用基于小平滑面非线性反演建模技术的射线束叠前深度偏移成像配套方法,提高了地震成像空间归位精度。研究结果表明:①基于小平滑面处理的数据可以有效保持炮检点位置真实性对旅行时准确计算;②通过构造层位、测井声波速度、近地表速度综合约束下建立的初始速度模型加上非线性层析反演技术能有效提高建模精度;③射线束法叠前深度偏移技术在"双复杂"地区对断裂带及陡倾角成像有显著提升。最终叠前深度偏移成果较好恢复地下构造真实形态,成像效果与井旁构造恢复结果整体符合,构造轴线和断层位置修正230 m,钻井证实在7 000 m深度相对误差控制在1%内,对双鱼石区块后期勘探开发井位部署及井轨迹优化具有指导意义。

With the advancement of exploration and development in Shuangyushi block,northwestern Sichuan Basin,drilling engineering transforms gradually from vertical wells in the early exploration stage to highly deviated horizontal wells in the development stage.Affected by some structural characteristics of surface and subsurface"double-complexity",most imaging data of prestack time migration cannot reflect certain structural morphology,furthermore,there is notable deviation in tectonic axis lines from drilling practices and prestack time migration.So,a method of ray-beam prestack depth migration imaging based on small-smoothing nonlinear inversion modeling was applied to improve spatial homing accuracy of imaging.Results show that(1)the data processed on the basis of small smooth plane can effectively reflect true shot position,further to calculate accurate travel time;(2)the initial velocity model established under the comprehensive constraint of structural horizon,logging acoustic velocity,and near surface velocity,combined with the nonlinear tomography inversion,can increase modeling accuracy effectively;and(3)the prestack depth migration technology based on ray beam method significantly improves the imaging of fault belts and steep dips in the"double-complexity"areas.The final prestack depth migration results can better reflect true morphology of underground structure,and the imaging effect is overall accordant with the reproduction result of near-well structure.The tectonic axis line and the fault location are corrected by 230 m,and drilling data also proves that a relative error at burial depth of 7000 m is controlled within 1%.These results are of guiding significance for Shuangyushi block to deploy well location and optimize wellbore trajectory in the later stage of exploration and development.