鄂尔多斯盆地深部煤层井壁失稳机理及钻井液对策

Mechanisms of Borehole Wall Instability of Deep Coal Seam in Ordos Basin and Drilling Fluid Countermeasures

针对鄂尔多斯盆地深部煤层井壁失稳问题,从岩心矿物组分、微观结构、理化性能和力学性质等角度揭示了纳林1井区本溪组8#煤储层井壁失稳机理,发现煤岩的割理裂缝结构及碳质泥岩的易水化分散矿物含量高是导致井壁失稳的主要原因。结合“多元协同”井壁稳定理论,提出“封堵性+抑制性+润滑性”的三效协同防塌钻井液技术对策。通过优选关键抑制剂、封堵剂和润滑剂,形成了适用于纳林1井区本溪组的防塌钻井液体系,并从基本性能、封堵性、抑制性和压力传递能力等角度进行了综合评价。该防塌钻井液流变性能良好,API滤失量仅为2.4 mL,高温高压滤失量仅为7.5 mL;抑制能力强,滚动回收率大于90%,16 h线性膨胀率小于5%;封堵性能优良,400μm开度裂缝的承压能力达到5 MPa。现场应用表明,新研制的防塌钻井液能有效抑制纳林1井区深部煤层坍塌,应用井段井径扩大率降低,机械钻速提高,无井下复杂事故发生,该套体系能够满足现场煤岩气钻井的需要,具有较好的推广应用前景。

In response to the problem of wellbore instability in deep coal seams in the Ordos Basin,the mechanism of wellbore instability in the 8#coal reservoir of the Benxi Formation in the Nalin 1 block was revealed from the perspectives of mineral analysis,microstructure analysis,physical-chemical properties and mechanical properties.Combined with the multiple synergy wellbore stability theory,a three-effect synergistic anti-sloughing drilling fluid technology strategy of plugging performance-inhibitive capacity-lubricity was proposed.By optimizing the key inhibitor,plugging agent and lubricant,an anti-sloughing drilling fluid system suitable for Benxi Formation in Nalin 1 block was formed.A comprehensive evaluation was conducted from the perspectives of basic performance,plugging property,inhibitory property,and pressure transmission ability.The laboratory test results show that the anti-sloughing drilling fluid formulation system had good rheological properties.The drilling fluid had API filtration rate of 2.4 mL,HTHP filtration rate of 7.5 mL,strong inhibitory ability.The percent recovery of shale cuttings was greater than 90%,16 h linear swelling rate was less than 5%.The drilling fluid had excellent sealing performance.Plugging of 400μm fractures with the drilling fluid renders the formation in which these fractures exist a pressure bearing capacity of 5 MPa.Field application has shown that the newly developed anti-collapse drilling fluid can effectively suppress the collapse of deep coal seams in the Nalin 1 well area,reduce the diameter expansion rate,increase the mechanical drilling rate,and prevent complex downhole accidents.It can meet the needs of coal and rock gas drilling on site and has good prospects for promotion and application.