煤系“三气”共采条件下的井壁稳定钻井液技术

Drilling Fluid Technology for Stabilizing Borehole in Coproduction of “Three Gases” in Coal Measures

煤系"三气"共采要求钻井液能同时解决煤层、致密砂岩和页岩地层的井壁稳定难题。在分析煤岩和页岩矿物组成的基础上,研究了正电性处理剂对煤岩表面Zeta电位的影响规律,优选出了能有效增加与页岩(煤岩)的接触角、降低钻井液表面张力的表面活性剂复配配方,并从流变性、滤失性、电性、润湿性、抑制性、储层保护和抗污染性能等方面对水基钻井液体系进行了综合评价。结果表明:有机正电胶和阳离子型表面活性剂均能降低毕节龙潭组煤岩的负电性;季铵盐类表面活性剂和有机硅表面活性剂均能将秀山龙马溪组页岩和毕节龙潭组煤岩由表面水润湿转变为油润湿;表面活性剂优化组合和无机正电胶(MMH-1)溶液能够有效阻缓页岩和煤岩的孔隙压力传递。所提出的MMH-1钻井液体系黏度适中,API滤失量仅为7 mL,对煤岩和页岩水化的抑制性强;储层伤害程度低,对煤储层的渗透率伤害率仅为10%,能将基浆煤岩气测渗透率降低率降低3.6%;抗污染能力强,能抗3%NaCl、1%CaCl_2和5%凹凸棒土(模拟钻屑);生物毒性低,对环境友好,满足煤系"三气"共采条件下的井壁稳定要求。

Coproduction of“three gases”in coal measures requires drilling fluid to have the ability to maintain the stability of coal beds,dense sandstones and shales penetrated by the well.The patterns in which positively charged additives affect the Zeta potential of the surface of coal are studied based on the analyses made to the mineral composition of coal and shales.Laboratory experiments have been done to find a compounded surfactants that are able to effectively enlarge the contact angle of shale/coal,and to reduce the surface tension of the drilling fluid.Comprehensive evaluation was done to the properties of the drilling fluid,such as rheology,filtration,electrical property,wetting property,inhibitive capacity,reservoir protection and contamination resistance performance etc.Evaluation of these properties showed that positively charged organic gel and cationic surfactants effectively neutralize the electronegativity of the coal in Longtan formation in Bijie County.Quaternary ammonium salt surfactants and organosilicon surfactants all are able to change the Longmaxi shale and Longtan coal from water wetting to oil wetting.The optimized mixture of surfactants and mixed metal hydroxide(MMH-1)solution are able to effectively retard pore pressure transmission in shales and in coal.An MMH-drilling fluid with moderate viscosity and API filter loss of only 7 mL showed strong ability to inhibit the hydration of coal and shales.This MMH-1 drilling fluid also showed very weak damage to reservoir permeability;permeability impairment caused by the drilling fluid was only 10%.Gas permeability reduction by base mud can be reduced by 3.6%using the MMH-1 drilling fluid.MMH-1 drilling fluid is resistant to contamination;in laboratory experiment the MMH-1 drilling fluid was able to resist contamination by 3%NaCl,1%CaCl2 and 5%attapulgite(to simulate drilled cuttings).MMH-1 drilling fluid is of low bio-toxicity and is environmentally friendly.All these advantages enable the MMH-1 drilling fluid to satisfy the needs for borehole stabilization in“three gases”coproduction from coal measures.