Abstract: The application range of oil-based drilling fluids is extensive.To reduce the cost of oil-based drilling fluids,a new low-cost formulation with a low oil-water ratio and low soil content was developed.This was achieved by selecting affordable oil-based base fluids,developing new single-dose high-efficiency emulsifiers,reducing the oil-water ratio,and decreasing the addition of organic soil.The performance of the new formulation was evaluated in the laboratory.According to experimental results,the oil-water ratio of the drilling fluid can be adjusted within the range of 65:35 to 85:15.The organic matter content is limited to 2.0% or lower,with a density of 1.4 to 2.2 g/cm³ and temperature resistance up to 200 ℃.The demulsification voltage is greater than 800 v,high temperature and high pressure fluid loss is less than 3 mL,and the unit cost of oil-based drilling fluid is reduced by over 15% compared to the fluid prepared with No.3 white oil.This fluid is suitable for -25 ℃ conditions and can meet construction needs during winter in the Liaohe Oilfield.The low-cost,low oil-water ratio,low-soil oil-based drilling fluid has been successfully applied in shale oil and tight oil formations in Liaohe Oilfield.Field application results demonstrate its stable performance,good plugging and anti-collapse capabilities,excellent emulsification stability,good low-temperature resistance,and significantly reduced unilateral cost.These research findings contribute to the expansion of the application scale of oil-based drilling fluid and can meet the technical requirements for the low-cost,safe,and efficient development of unconventional oil and gas reservoirs.

Key words: low cost, base solution, low oil-water ratio, low soil content, oil-based drilling fluid, low temperature resistance, Liaohe Oilfield, tight oil and gas reservoir