Overview：

FLATPRO is a second generation "flat rheology" synthetic based drilling fluid system suitable for deep water and ultra-deep water drilling operations. It has been developed based on the complementary mechanism of viscosity-temperature properties of temperature-sensitive polymer and modified clay. It has excellent low temperature stability, with stable rheological properties at a wide range of temperatures (2~180℃). It offers the benefits of low ECD and low formation impairment. It has been successfully used in the South China Sea for deep water wells, ultra-deep water wells and deep water extended reach wells. It has successfully overcome the technical challenges from narrow drilling window, hole cleaning, high ECD and the difficulty of tripping. As a result, it has significantly reduced operational downtime or NPT.

Applicability：

Temperature: 2~220 ℃；Density: 0.95~2.20 g/cm3

Characteristics：

Improved rheology at low temperatures;Stable rheological properties under large temperature variations；Small variation of ECD, only 0.03 g/cm3 ~ 0.04 g/cm3 ；Low biotoxicity.

Background:

An ultra deep well in Yongle Block, South China Sea, with water depth of 2619m, mud line temperature of 1.9 ℃, and bottom hole temperature of 107℃, is operated with deep-water  rheological drilling fluid  FLAT-PRO oil-based drilling fluid.

Challenge:

1. The fluidity of low temperature drilling fluid becomes worse, and the rheological stability under large temperature difference;

2. The operation window is narrow, the minimum is only 0.09g/cm3; deliver equivalent circulating density (ECD) benefits, while minimizing any weight fluctuation risk。

3. The water depth is 2619m, and the super long riser requires good suspension of drilling fluid to solid phase for large environmental control

4. Multiple faults are encountered during drilling, which is prone to leakage and affects downhole safety and subsequent operations

Solution:

1. It has good rheological property at low temperature and is stable in a wide temperature range of 0-180 ℃;

2. Deep water oil has good viscosity temperature characteristics, and ECD of the system changes little;

3. The flow pattern regulator, emulsifier and organic soil are synergetic, the system shear changes little with temperature, and the low viscosity anti settling stabilization technology ensures good suspension of solid phase;

4. The leakage prevention and pressure bearing measures are appropriate. Pressure bearing plugging agents such as MOSTRH and MOSHIELD greatly improve the pressure bearing performance of the system.

Job results:

1.The technical problems such as poor low-temperature rheology in deep water, gas hydrate hazard, wellbore instability and leakage have been successfully solved, and the "zero" accident rate has been achieved;

2.The rheological property is stable during drilling, the ECD change of the whole well is only 0.03g/cm3, the returned drilling cuttings are formed, the sand production is good, the whole well is directly tripped, and there is no sand setting

3.The construction of deep-water extended reach wells continued, and the operation quality was highly praised by the operators. "The oil chemical constant rheological drilling fluid has achieved constant rheological performance control under the worst seabed temperature and the most severe drilling conditions, and its rheological change trend is just like its name" David Triolo, Haskey drilling manager, highly praised the FLAT-PRO system