页岩气井钻井液井眼强化技术

页岩气地层有着易表面水化剥落掉块、微裂缝发育、脆性好而裂缝易压裂等理化特性，目前，页岩气开发中常用的油基和合成基钻井液体系，起到了很好的防塌防卡效果。但随着开发的深入和地层特性的变化，如钻遇破碎带、裂缝异常发育的地层，采用油基体系仍然会出现大量掉块和严重井塌。为了解决易破碎性地层又垮又漏的复杂情况，需要及时有效地强化已形成的井眼。在钻井液中引入井眼强化剂YH11和BT100，室内实验对加入2种处理剂的钻井液进行了评价，研究出了一套适用于页岩气钻井液的井眼强化技术。该钻井液密度可调范围大，现场可控制在低密度范围1.14~1.50 g·cm-3，该体系抑制能力强，在防漏方面实现了低密度钻进，并且该钻井液体系具有良好的成膜封堵效果，解决了井壁稳定和承压能力低的矛盾，减少了井下复杂情况，确保了井下安全，进一步促进了机械钻速的提高。室内实验和现场应用都表明，井眼强化剂能及时胶结破碎性地带和封堵微裂缝而使井壁变得更致密，大大降低井壁的孔隙度和渗透性，有效阻止液柱压力向井壁孔隙的传递和阻止滤液的深度侵入，减少井壁支撑力的损失，获得防塌和防漏的双重效果。 

Borehole Wall Strengthening with Drilling Fluids in Shale Gas Drilling

Formations drilled in shale gas drilling are full of micro fractures and are brittle, and are therefore easy to hydrate and slough. Oil base drilling fluids and synthetic base drilling fluids have been commonly used in shale gas drilling, and are effective in preventing borehole wall sloughing and pipe sticking. However, when drilling into a broken belt or into formations with abnormally developed fractures, large amount of sloughing and severe borehole wall collapse still happen even oil base drilling fluids are used. To address borehole wall collapse and mud losses when drilling broken formations, the borehole wall should be strengthened promptly and effectively. A drilling fluid treated with two borehole wall strengthening agents, YH11 and BT100, was tested for its capacity to strengthening borehole wall. The test results showed that this drilling fluid formulation is suitable for shale gas drilling. The density of this drilling fluid is adjustable in a range of 1.14-1.50 g/cm3. It has strong inhibitive capacity, and is capable of preventing mud losses by drilling at low densities. Good filming and sealing performance of the drilling fluid helps resolve the problem of stabilizing formations with low pressure bearing capacity. Minimizing of downhole troubles and downhole safety insurance help enhance rate of penetration. Both laboratory experiment and field application showed that YH11 and BT100 are able to strengthen borehole wall by promptly cementing the broken formations and plugging the fractures. Cementing and plugging of the formations with YH11 and BT100 greatly reduce the porosity and permeability of the formations, effectively restraining the transfer of hydraulic pressure of mud column into the pores of formation and the invasion of mud filtrates into the depth of formation, hence minimizing loss of pressure supporting the borehole wall. The use of YH11 and BT100 has double effects of preventing borehole wall collapse and mud losses.