黔北地区窄陡型向斜页岩气水平井地质导向技术对策

Shale gas horizontal well geosteering technologies and countermeasures research in narrow and steep syncline formations of northern Guizhou area

黔北地区五峰组-龙马溪组页岩地层残留于窄陡型向斜中,具有地层速度变化大,地震资料靶点预测精度低;地层倾角变化频,地层走向及轨迹难以把控;地层稳定性差,井眼扩大严重等难点。增大了地质导向难度,水平井钻遇率低。针对这些问题,梳理分析了实钻中地质导向遇到的难点,通过井震结合,完善三维地震速度模型,精确提取各地层、各方位地层视倾角;实钻中通过多元厚度建模,不断矫正细化对靶点深度的预测,优化随钻三维轨迹;进入箱体后,强化地球物理响应特征,对随钻曲线进行正演提取及反演对比,利用多元元素谱及成像技术精细刻画箱体成像特征。在7口井的钻探应用中靶点误差与设计降低至25 m,优质页岩钻遇率提高到99.2%,箱体钻遇率从87.6%提高至96.5%,其中3口实现了中靶率、优质页岩钻遇率和箱体钻遇率3个100%的地质导向成果。类似于黔北地区这种窄陡型残余留向斜地质导向难点通过该套技术对策可以及时避开小褶皱等细微构造变化,有效保障水平井箱体钻遇率,为水平井地质导向提供了扎实的技术支撑。

Northern Guizhou area is located at the edge of the Sichuan Basin,and its structure belongs to Wuling fold area.Wufeng Longmaxi shale stratum is in a series of narrow and steep residual synclines,and the main developed shale stratum is within five meters of the bottom of the Longmaxi Formation,with a thin thickness.Due to the complex surface and underground geological conditions,the seismic velocity changes in this area,and the horizontal and vertical changes in various geological factors,such as the stratum dip angle and thickness,are large,so the drilling rate of horizontal wells in this area is relatively low.In this paper,the difficulties encountered in horizontal well geosteering in the narrow and steep residual syncline are sorted,and the modelling of velocity,structure,thickness,dip angle and curve was carried out.Combined with the element change law and element imaging technology,the track while drilling horizon was identified step by step to improve the hit target rate and drilling encounter rate.The actual drilling results show that the deviation from the geological design was reduced within 25 meters,the drilling encounter rate of high-quality shale was increased to 99.2%,and the drilling encounter rate of the box was increased to 96.5%from 87.6%.Three wells of them achieved the geosteering achievements of hit rate 100%,high-quality shale encounter rate 100%,and box body encounter rate 100%.In areas similar to the narrow and steep residual syncline geosteering difficulty in the northern Guizhou area,the application of this set of technical countermeasures can avoid subtle structural changes such as small folds in time and effectively ensure the box drilling rate of horizontal wells,which can provides solid technical support for horizontal well geosteering.