High-Performance Oil-Based Drilling Fluid Technology for Horizontal Wells in the Madong Oilfield, Junggar Basin

The build-up section and horizontal section drilling in horizontal wells of the Madong Oilfield, Junggar Basin was challenged by problems such as pipe-string sticking during trip operations, wellbore instability, and low ROP caused by the hydration of mudstone, abnormal pressure, and an abundance of glutenites. Therefore, high-performance oil-based drilling fluid was accordingly investigated. Based on the reservoir characteristics of the Madong Oilfield and the drilling requirements of the medium-long horizontal sections, XZ high-performance oil-based drilling fluid was hereby formulated, and indoor laboratory experiments were carried out to evaluate its weighting, temperature resistance, shear strength improving, sealing/pressure-bearing, anti-pollution and anti-freezing performances. The results showed that this oil-based drilling fluid system exhibited stable rheological properties and an adjustable shear force between the density of 1.35–2.01 kg/L. The new fluid exhibited good thermal and freezing stability, low temperature resistance of up to –24 ℃, and high temperature resistance of up to 180 ℃. The emulsification stability was good, and the demulsification voltage was generally above 1 000 V. The anti-pollution ability was strong, the anti-cuttings pollution concentration was ≥20.0%, the anti-formation water pollution concentration was ≥20.0%, and the anti-cement pollution concentration was ≥10.0%. Further, the new drilling fluid system had strong sealing ability. When using sand discs with a diameter of 120 and 150 μm for pressure-bearing sealing, the pressure-resistance of both discs could reach 15 MPa. This system was applied in 4 of the wells in the Madong Oilfield. After the application of the new fluid, perfect borehole stability was achieved, the hole enlargement rate of the build-up section was only 3.55%, the trip operation was completed smoothly, and the average ROP was 79.0% higher than that of the same horizon drilled with water-based drilling fluid. A remarkable drilling speed-up effect was observed. The research results showed that the application of XZ high-performance oil-based drilling fluid can solve the technical problems in the development of the glutenite reservoirs in the Madong Oilfield and satisfy the needs of safe and fast drilling in the long horizontal section of this oilfield.