Evaluation and Field Application of Weighting Agents for Ultra-High Density Oil Base Drilling Fluids

The pressure coefficient of the Paleogene, Cretaceous and Jurassic systems in the south rim of the Junggar Basin is in a range of 2.40-2.65 g/cm³. An ultra-high density oil base drilling fluid with excellent performance is in urgent need to ensure safe drilling in this area. Using environmental scanning electron microscope and laser particle size analyzer, the micro morphology and particle size distribution of the common barite, micronized manganese ore and micronized barite were analyzed. The principles of reducing the viscosity of drilling fluids with micronized weighting agents are also analyzed. A mixture of different weighting agents in optimum ratio for formulating ultra-high density oil base drilling fluids was made through laboratory experiment, that is, common barite: micronized manganese ore = 7∶3. An ultra-high density oil base drilling fluid was formulated and its high temperature settling stability and water contamination resistance were evaluated. The experimental results showed that the ultra-high density oil base drilling fluid has good high temperature settling stability; after standing for 24 h at a constant temperature, the difference between the density of the top and the density of the bottom of the oil base drilling fluid was 0.01-0.02 g/cm³. After standing for 120 h at a constant temperature, the difference between the density of the top and the density of the bottom of the oil base drilling fluid was 0.10-0.14 g/cm³. The oil base drilling fluid is resistant to the contamination of 15% water invasion. Field operation showed that a 2.65 g/cm³ ultra-high density oil base drilling fluid manifested itself good performance in the whole drilling process, with no troubles encountered downhole.