Design of drilling fluids is crucial to extended reach drilling (ERD) with the challenges including borehole stability, hole cleaning, lubricity and equivalent circulating density (ECD) management. Normally, oil-based drilling fluids would be the best choice for an extended reach well with a horizontal displacement of 8000m. However, the Liuhua Oilfield is located in the South China Sea, an environmentally sensitive area. It is necessary to develop the high performance water-based drilling fluids which offer the performance to match oil-based drilling fluids.

The integrated design proposal of water-based drilling fluids for the well Liuhua 11-1-B3 ERW4 with a horizontal displacement of 8000m (26247ft) is discussed in this paper, including design criteria, the formulations and the parameters of performance of the drilling fluids in each interval of the well. The more attention is paid to the 12 1/4-in. open hole section, where a kind of high performance water-based mud (HPWBM) is prepared. The two newly developed chemical additives, an amine polymer and an aluminum complex, are added in the KCl/polymer drilling fluid which was successfully used in the extended reach wells with a horizontal displacement of 6000m in this oilfield. In addition, a membrane-forming agent is added in this mud system and an optimized combination of lubricants was used to improve the lubricity of the drilling fluid.

Numerous experiments were conducted to evaluate the various properties of this novel water-based drilling fluid. The experimental results indicate that it has excellent rheological properties, very low filtration rate, good lubricity and strongly inhibitive character to shale, which are very close to the commonly used oil-based drilling fluids.

The results of risk analysis show that the design proposal of this water-based drilling fluid is feasible and can meet the drilling requirements of ERD with a horizontal displacement of 8000m open hole section in this area with less pollution of the sea and without increasing more cost.

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