准噶尔南缘膏泥岩地层井壁失稳机理研究*

准噶尔盆地南缘山前安集海河组和紫泥泉子组地层含有大量膏泥岩和泥岩,且存在复杂的破碎带,是该地区钻井过程中发生遇阻、卡钻、井漏等井下复杂事故的主要层段。从岩心粘土矿物组分、微观结构、岩石力学性能、岩屑分散膨胀性能等方面分析该层段的失稳机理。研究认为：安集海河组和紫泥泉子组地层均具有粘土含量(30%)、伊/蒙混层(57%)、混层比高(55%)是地层发生非均匀水化膨胀失稳的主要原因；岩屑清水热滚回收率和线性膨胀率可见地层具有高分散高膨胀的特点,极易造成井壁坍塌及钻井液性能恶化；岩心抗压强度较低,经水基钻井液浸泡后破碎或者产生裂纹,油基钻井液浸泡抗压强度下降,说明岩心本身的抗压强度低也是地层不稳定原因；另外,地层孔隙压力高,钻井液安全密度窗口窄,钻井液密度控制不当也是导致地层失稳(漏失和坍塌)的重要原因。

Study on borehole instability mechanism of plaster mudstone formation in Ssouthern margin of junggar basin

SIn the southern margin of the Junggar Basin, the Anjihaihe Formation and the Zini Springzu Formation contain a large amount of mudstone and mudstone, and there are complex crushing zones, which are complicated accidents such as encountering resistance, stuck drilling, well leakage in the drilling process. Major interval. The failure mechanism of this section is analyzed from the aspects of core clay mineral composition, microstructure, rock mechanics performance, and dispersive and swelling properties of cuttings. The results show that the stratum of the Anjihaihe Formation and the Zibiquunzi Formation have the clay content (30%), the mixed layer (57%) and the mixed layer ratio (55%), which are caused by the nonuniform hydration swelling instability The main reasons are as follows: the heat recovery rate and linear expansion rate of cuttings show that the formation has high dispersion and high expansion characteristics, which can easily lead to the collapsing of wellbore and the deterioration of drilling fluid performance; the core compressive strength is low; after water-base drilling fluid is soaked, Cracking or cracking, oil-based drilling fluid soak compressive strength decreased, indicating that the core of the compressive strength is also the cause of formation instability; In addition, the formation of high pore pressure, drilling fluid safety density narrow window, drilling fluid density control is also caused by improper The formation instability (loss and collapse) of the important reasons.