沁南区域煤层气水平井瓜尔胶钻井液技术

针对沁南区域15号煤层水平井钻井采用清洁盐水和常规聚合物钻井液施工时的井壁坍塌和储层伤害等问题，在分析储层特征及钻井技术难点的基础上，研发了瓜尔胶钻井液和生物酶破胶液。通过优化瓜尔胶加量和评价瓜尔胶的耐盐性能，并复配其他处理剂，形成了瓜尔胶钻井液；通过优选生物酶种类、优化生物酶和助排剂的加量，形成了生物酶破胶液。室内试验表明，瓜尔胶钻井液具有良好的流变性和耐盐性能，可大幅提高煤岩抗压强度，在低温下易破胶，破胶后残渣小于300 mg/L，煤岩的渗透率恢复率达85%以上。沁南区域煤层气水平井应用瓜尔胶钻井液后，井壁稳定性良好；配合生物酶破胶液可以实现低温破胶，且单井日产能提高15%以上，具有较好的储层保护效果。研究结果表明，瓜尔胶钻井液可实现煤层长水平段钻井的顺利施工，完钻后可低温破胶，为易塌煤层气水平井钻井施工提供了一种新的储层保护方法。 

Guar Gum Drilling Fluid Technology for Coalbed Methane Horizontal Wells in Qinnan Area

Wellbore collapse and reservoir damage occurred when clean brine and conventional polymer drilling fluids were used in drilling horizontal wells of No. 15 coal seam in Qinnan Area. In view of this, according to reservoir characteristics and challenges encountered during drilling, a guar gum drilling fluid and a bio-enzyme gel breaking fluid were developed. Specifically, the guar gum drilling fluid was formed by optimizing the dosage of guar gum, evaluating the salt tolerance, and integrating with other treatment agents. And the bio-enzyme gel breaking fluid was produced by optimizing types and dosage of bio-enzyme and cleanup additive. The laboratory test showed that the guar gum drilling fluid had good rheological and salt tolerance properties. It could greatly improve the compressive strength of coal and rock, and easily achieve gel breaking at low temperatures, with residues after breaking less than 300 mg/L.The permeability recovery rate of coal rock was more than 85%. In terms of the application of the guar gum drilling fluid in coalbed methane (CBM) horizontal wells in Qinnan Area, the fluid showed positive wellbore stability. In addition, it not only achieved gel breaking at low temperatures but also improved the daily productivity of a single well by more than 15% after integrating with the bio-enzyme gel breaking fluid, which indicated a favorable reservoir protection effect. The research shows that the guar gum drilling fluid can ensure smooth drilling of long horizontal sections in coal seams and achieve gel breaking at low temperatures after drilling, which provides a new reservoir protection method for drilling horizontal wells in fragile coal seams.