高密度无土相油基钻井液

High Density Clay-free Oil Based Drilling Fluid

高密度油基钻井液高温下重晶石易沉降,导致体系稳定性变差,传统方法采用高浓度有机土来解决,但其会引起钻井液黏度过高,造成ECD升高而引发井漏等复杂情况。针对以上问题,研发了一种具有强电稳定性能、增黏效果的小粒径乳化剂DEMUL,并开发了一种高密度无黏土相油基钻井液体系,通过加入DEMUL、苯乙烯-丁烯/丁二烯-苯乙烯嵌段共聚物(SEBS)与提切剂的协同作用,达到提高高密度油基钻井液的稳定性能,且配方简单、处理剂加量少。研究结果表明,该钻井液在200℃下老化160 h也能保持良好的流变性能,160℃恒温静置336 h后沉降因子为0.5074,表现出良好的稳定性,且具有良好的抑制性能和极压润滑性能。该钻井液体系在川渝页岩气某高密度水平井进行了应用,钻井过程中该体系流变性能稳定,携砂性能良好,抑制性能强,未出现井下复杂情况。

Barite in oil based drilling fluids at elevated temperatures is easy to sag,resulting in poor stability of the muds.Conventionally this is solved by adding more organophilic clay.High clay content in the mud results in high mud viscosity and high ECD,causing mud losses to happen.To deal with this problem,a small particle size emulsifier DEMUL with high electric stability and viscosifying property has been developed to formulate a high density clay-free oil based drilling fluid.The drilling fluid was treated with DEMUL,SEBS(a styrene-butene/butadiene-styrene block copolymer)and a gellant,the synergy of these additives helps improve the stability of the oil based drilling fluid.This drilling fluid has simple formulation,and each additive is added at a low concentration.Laboratory experiment showed that the oil based drilling fluid still retained good rheology after aging at 200℃for 160 h.After standing still at 160°C for 336 h,the settling factor of the drilling fluid was 0.5074,indicating that the drilling fluid had good stability.Furthermore,this drilling fluid also has good inhibitive capacity and extreme-pressure lubricity.This drilling fluid has been used in drilling the horizontal section of a high pressure shale gas well in Chuanyu area.During the whole drilling operation,the drilling fluid showed stable rheology,good sand carrying capacity and high inhibitive capacity,and no downhole trouble has ever been encountered.