The horizontal well of Jimsar shale oil with a long openhole wellbore adopts the two-casing-section structure，and the openhole wellbore of the second casing section is 4 000 m long，with a horizontal wellbore over 2 000 m. The used drilling fluids are oil-based，and wellbore collapse tends to occur when drilling the Badaowan and Jiucaiyuanzi Formations and leads to movement resistance，sticking of tools，lost circulation，etc. To overcome the wellbore collapse in complex formations，in accordance with the lithological characteristics of formations，the main factors affecting wellbore stability such as clay mineral composition and micro-fracture development were analyzed，the mechanisms of wellbore instability of such collapse-prone formations were clarified，and the anti-collapse theory of oil-based drilling fluids was developed，which features "multi-element cooperation and broad-spectrum plugging". Based on the proposed theory，the anti-collapse formulation of oil-based drilling fluids was improved by optimizing the materials such as asphalt products，ultra-fine calcium carbonates and nano-plugging agents. The laboratory tests show that the performance parameters of the drilling fluids meet the operation requirements and the plugging performance is excellent. Specifically，the drilling fluid density is 1.52-1.62 g/cm³；funnel viscosity，80-100 s；yield point，8-13 Pa；emulsion-breaking voltage，above 500 V；oil-water ratio，（80：20） to （85：15）；API fluid loss，≤ 1.5 mL；HTHP fluid loss at 120°C，≤ 2 mL. The presented anti-collapse system of oil-based drilling fluids has been successfully applied to Jimsar shale oil horizontal wells with a long openhole wellbore. The average borehole enlargement rate of the openhole wellbore and the rate of downhole complex issues were 3.03% and 0.55% respectively. The anti-collapse system effectively ensured the drilling safety of the build-up and horizontal wellbores.

The fracturing flowback fluid in Sulige Gasfield is characterized by large volume，complex composition and great difficulties in treatment. After being treated by simple processes of oxidation，flocculation and sedimentation，the fracturing flowback fluid still fails to meet the standard for direct discharge or recycle. Besides，the need for storage of the treated fluid makes the operating cost increase. Therefore，more processes such as reduction and adsorption are added，so that the treated fluid can meet the standard for repreparing new fracturing fluid. Experimental results show that the concentrations of boron，calcium and magnesium ions which impair the performance of fracturing fluid in the treated fluid are obviously reduced and the quality of treated fluid is obviously improved. The re-prepared fracturing fluid system has a viscosity of 150 mPa∙s，satisfactory compatibility and gel breaking performance，and an average damage rate of about 17%. All of these indicators meet the requirements in relevant standards. In addition，the recycle technology of fracturing flowback fluid has been successfully applied in Sulige Gasfield.