Research And Application Of Anti-collapse Drilling Fluid In Complex Coal Seam

In the view of the difficult problems of wellbore stability during the drilling process in the Kirkia block of Tuha oilfield and Dibi block of Tarim oilfield,the fabric structure and physical and chemical properties of the coal seam are analyzed.The main reasons of the borehole instability of the coal slime interbed are analyzed from the aspects of physics,chemistry and mechanics.One is under pressure,the water enters the coal-rock and changes stresses.Another one is the water wedge effect makes the coal loose and damage the structure.And the water discharge into the coal slime,cracks in the coal seam is formed,the strength and elastic modulus of coal are reduced at the same time.Based on the principle of multi synergy wellbore stability,a multi cooperative anti-collapse drilling fluid technology is proposed,which includes plugging consolidation-reasonable density-inhibiting hydration-reasonable technological measures.The optimized formula of BH-WEI organic salt drilling Fluid was obtained by indoor optimization experiment:water+0.5%Na₂CO₃+3%Bentonite+0.1%Positive glue+1.5%KLS-?+0.1%BZ-BBJ+3%BZ-YFT+2%BZ-YRH+2%BZ-DFT+4%Fine calcium+5%BZ-YJZ-I+Barite.The system has outstanding inhibition and plugging performance,good rheological property at high density.High temperature and high pressure filtration at130/3.5MPa are less than before.The optimized BH-WEI fomate drilling system was used as the main formula,and the field test was carried out in the Kirkia 283 well and Dibei 1 well.During the drilling process,there is no complicated case such as wall failure,and the drilling period is lower than the adjacent well.The drilling cycle had been shortened and significant economic benefits had been achieved in oilfield.This technology has a broad application prospects.