Study On Oil - Based Drilling Fluid System And Its Application In Shallow Horizontal Wells In Western

For shallow long horizontal well drilling in the western Sichuan, and sandstone and mudstone interlaced lead to borehole instability, high cost and other problems, we summarized the application results of the imitation oil-based drilling fluid which had been used and made out the property requirement of the drilling fluid for horizontal well. Then, we optimized the system formula and studied the inhibitive mechanism of the main treating agents. Finally, the optimized drilling fluid formula was applied in field.Polyamine was chosen as the main inhibitor and methyl glucoside(MEG) as lubricant, filtration reducer and the second inhibitor. In the laboratory research, we picked up the best inhibitor NH-1with the evaluation method for polyamine and the dosage was0.8-1%. Besides, we studied the relationship between MEG and inhibition, lubrication, filtration and the dosage of it was3-5%, compared with8-12%in ex-formula, the cost was greatly reduced. Finally, the best formula of imitation oil-based drilling fluid was made out by optimizing other treating agents.The inhibitive mechanisms of the main treating agents were studied. By particle size testing, the distribution curve moved to the right side after adding polyamine, which means bentonite particles get bigger and hydration dispersion is inhibited. By zeta potential testing, small dosage of polyamine will reduce the zeta potential of bentonite particles, decreasing hydration repulsion and inhibiting expansion. Besides, wet X ray diffraction showed that small dosage of polyamine reduced interlayer distance, indicating that polyamine can effectively inhibit hydration in a small dosage.We also studied the MEG adsorption on bentonite with UV spectrophotometry and found that MEG adsorbs to equilibrium in a short time and inorganic salt can improve the adsorption ability of MEG. Besides, MEG is physical adsorption and the saturate adsorption is1.273g per bentonite at the temperature of70℃.The optimized drilling fluid was applied in horizontal wells, the imitation oil-based system showed good performance in rheology, filtration, lubrication and other aspects in horizontal well drilling in the western Sichuan by testing samples from field. This combination of polyamine and MEG shows great advantage, inhibiting hydration expansion in horizontal borehole well and preventing well collapse. This drilling fluid meets the needs of long horizontal well construction and there were no complex underpit circumstances in field application.