超低渗透钻井液提高地层承压能力机理研究

通过超低渗透钻井液高温高压条件下侵入岩石深度实验、侵入岩石深度实验后的岩心清除泥饼前后岩心承压能力实验、提高裂缝承压能力实验、钻井液中加入零滤失井眼稳定剂前后岩心滤失量随时间变化关系实验,以及超低渗透钻井液在滤液进入岩心浅层后封堵孔隙的电子显微照片分析可知,超低渗透钻井液提高地层承压能力机理是利用特殊聚合物处理剂,在井壁岩石表面浓集形成胶束,依靠聚合物胶束或胶粒界面吸力及其可变形性,封堵岩石表面较大范围的孔喉,在井壁岩石表面形成致密超低渗透封堵膜,有效封堵不同渗透性地层和微裂缝泥页岩地层.超低渗透钻井液在井壁表层能快速形成渗透率为零的封堵层,在井壁的外围形成保护层,钻井液及其滤液完全隔离不会渗透到地层深处,可实现接近零滤失.零滤失井眼稳定剂通过在井壁表面形成超低渗透膜及增强内泥饼封堵强度大幅度提高了岩心承压能力,这样在现场应用中就能提高漏失压力和破裂压力梯度,扩大安全密度窗口.

Mechanism study on Ultra-low Invasion Drilling Fluid for improvement of formation pressure-bearing ability

In order to know how the ultra-low invasion fluid improve formation pressure-bearing ability,a quantity of tests were performed such as the test of invading depth of fluid at the high-temperature and high-pressure,the test of pressure bearing ability of rock before and after the cake formed during the fluid invading into the rock being cleared,the test of improving fracture pressure-bearing ability,the test of core filtration before and after the fluid being added into zero loss wellbore stable agent and analyzing the electron microphoto of filtrate plugging into shallow layer of core.The results from these tests indicated the ultra-low invasion fluid can improve formation pressure-bearing ability by using particular polymer additives,which can gather on the surface of holewall rock to make micellar.The micellar or colloidal particle produced can plug many pore throats and form ultra-low invading plugging membrane on the surface of core by means of interfacial attraction and deformable properties,so various permeable formation and fractured shale are plugged.Meanwhile,the ultra-low invasion fluid can quickly generate blocking layer with zero permeability in shallow holewall and produce protecting layer in outer holewall.Thus the fluid and filtrate can not invade the deep formation so that the fluid filtrate is close to zero.Zero filtrate wellbore stable additives greatly improve the pressure bearing capability of core by forming ultra-low permeable membrane on the holewall,therefore,the loss pressure and fracture pressure gradient can be enhanced,and the safe density window can be amplified.