随钻方位伽马测井在水平井地质导向中的应用——以延113-延133区块为例

Application of azimuth gamma-ray logging while drilling in geosteering of horizontal wells:a case study of Yan113-Yan133 block

延113-延133区块山2^(3)致密砂岩气藏纵向上非均质性强,平面上三角洲前缘水下分流河道沉积的透镜体状砂岩极为普遍,且局部微构造发育,采用常规随钻伽马指导井眼轨迹调整易导致水平井钻出储层;而随钻方位伽马测井利用多个伽马探测器,可同时提供4个方向随钻伽马数据。研究表明:钻遇岩性变化时,方位伽马曲线表现为上下伽马分离,上伽马较早由20~70 API抬升至80~120 API,即钻头上切泥岩,下伽马较早由20~70 API抬升至80~120 API,即钻头下切泥岩。据此可及时判断钻头与地层的接触关系,精确指导井眼轨迹调整,减小井下盲钻风险,提高储层钻遇率。

S23 tight sand gas reservoir in Yan113-Yan133 block is characterized by strong heterogeneity in longitudinal direction,widespread lenticular sandstone deposited by distributary channel in plane,and micro-structure development in local area.It’s easy for horizontal wells to drill out of reservoir by using conventional gamma ray while drilling to guide well trajectory adjustment,while multi-gamma detectors are used in azimuth gamma logging while drilling,which provides four directions gamma data at the same time.The results show that the azimuthal gamma curves will separate when drilling lithology changes.The up-gamma rises from 20~70 API to 80~120 API early,which means the bit up-cuts mudstone,and the down-gamma rises from 20~70 API to 80~120 API early,which means the bit down-cuts mudstone.According to this,the contact relationship between bit and formation is judged in time,the trajectory adjustment is guided accurately,the risk of blind drilling is reduced,and the drilling encounter rate of reservoir is improved.