The Development and Application of Novel Water-Based Drilling Fluid for Complex Pressure System Formation in the South China Sea

The Y oilfield reservoir is characterized by ultra-depleted and multiple pressure systems in each well section. If conventional PLUS/KCL drilling fluid used directional drilling, the following problems are found: rheological stability of not sufficient, resulting increased viscosity thickening after aging, single plugging material may cause loss-circulation when differential more than 26 MPa, poor protection effects. To solve above problems, based on formula, a system suitable for multi-pressure was formed optimizing addition treating agent to improve fluid, compound combination ability, particle size distribution temporary effect. laboratory test evaluation showed that optimized had fine capacity, intrusion depth only 4.1 cm natural core at 120 °C/35 MPa/12 h, effectively reducing risk loss-circulation. permeability recovery rate cutting off polluted end 90%, indicating effect good. performance stable, cuttings rolling over 90%. Field application without any or wellbore instability, production all wells over-matched, solving problem ensuring safety damage under systems.