Baroid’s latest clay-freeINNOVERT™ synthetic-base fluid (SBF), based on clay-free ACCOLADE® technology, has delivered exceptional performance on the first nine wells of a new contract with a major operator in ultra-deep water over 5,000 feet offshore West Africa. Based on a low viscosity n-alkane base fluid and built without using the regular organophilic colloidal additives used in conventional invert emulsion fluids, this state-of-the-art drilling fluid represents a quantum leap in deepwater drilling fluid performance.
The ultra-low fracture gradient of subsea formations in deep water offshore Angola places severe limitations on mud weight and equivalent circulating density (ECD). The difficulty of operating in this narrow mud weight/fracture gradient window is made worse by the impact of cold temperature on the drilling fluid in the riser, resulting in markedly increased rheological properties and ECDs. As a result, when using conventional drilling fluid systems, the pressure required establishing circulation in the well after static periods, or to run and cement casing strings in the well construction process, can be high enough to break down the formation with loss of drilling fluid downhole.
Originally introduced in the Gulf of Mexico to cut the high cost of SBF losses in deepwater drilling, while ensuring compliance fully with U.S. Environmental Protection Agency (EPA) regulations, ACCOLADE drilling fluid technology was transferred to West Africa and used to overcome new challenges via the development and introduction of the alkane-based INNOVERT SBF. The introduction of this system helped secure two new contracts with a major operator offshore Angola.
Endowed with a substantially lower tendency for cold temperature gelation, this fluid has helped achieve an ECD equal to 0.2-0.3 ppg above surface mud weight compared with the 0.4-0.6 ppg over mud weight typical of the conventional SBFs previously used by the operator concerned. Pressure fluctuations due to pipe movement and pump operation have been far lower and are virtually negligible in many cases. As a result, drilling fluid losses downhole have bee 60% lower compared with previous wells in the same block using conventional SBF. Offset wells averaged losses of over 2,000 bbl per well. The contingency liner string in the top-hole section of the original drilling programme has not been required.
Extensive ongoing development work during 2005 led to the achievement of zero per cent formation damage in return permeability tests conducted independently by the operator. Formulated with lower product concentrations and designed to minimize downhole losses, the new system requires far less material to be shipped to the rig than conventional systems, meaning fewer crane lifts, reduced transportation requirements and reduced worker exposure to safety hazards.
Customer testimonials on the fluids performance:
“Just to let you know how pleased operations are with the way the mud behaved during the recent [13 3/8”] casing operations. Lower pressures were seen and the much dreaded losses did not occur. The new system is meeting expectations.”
“No pressure spike when breaking circulation at the BOP after 5 days of logging [in 12 ¼” hole].”
“Your [Baroid’s] mud far exceeds the mud systems we have seen before.”
By Charles Cameron, Halliburton
