First Application of the Synthetic-Based Drilling Fluid BIODRILL S in Block Kenli of Bohai Oilfield

Drilling operation in the Block Kenli 9-1 of the Bohai Oilfield has long been faced with high risks of borehole wall collapse resulted from complex formation lithologies, fault zones, shales that are easy to hydrate and disperse, as well as sandstones in which tight hole problem is frequently encountered. To deal with the borehole wall collapse problem a BIODRILL S synthetic based drilling fluid has been formulated. The BIODRILL S synthetic based drilling fluid is formulated with a base oil which is synthetic oil of choice, a composite plugging additive PF-MOSHIELD, as well as other drilling fluid additives, taking into account the formation lithology and environmental protection requirement. The BIODRILL S drilling fluid has good rheology , and is resistant to 26% calcium contamination and 15% cuttings contamination. Furthermore, it has excellent plugging capacity, settling stability and lubricity. The HTHP filter loss tested on a sand plate tester is 3.2 mL. The sag index of the mud after standing for 7 d is 0.53, and the extreme coefficient of friction is 0.082. BIODRILL S was first used in the Block Kenli 9-1. The application showed that: 1) the BIODRILLS can be used to solve the shale hydration problem and the tight hole problem in the sandstone formation encountered previously in this block; the drilled cuttings produced in drilling the formations in and above the third section are intact, with sizes distributed between 4 cm and 7 cm. 2) Hole cleaning is well done with the BIODRILL S drilling fluid, the ratio of YP/PV is greater than 0.59 Pa/mPa∙s, the φ₆ and the φ₃ reading are all greater than 9, and the drilling fluid has good shear thinning property. All these properties result in good hole cleaning and the prevention of the occurrence of cuttings bed. 3) The drilling fluid has excellent lubricity, making possible the direct tripping (out of hole) through the high angle (55°, 70° and 67°) well sections.