Because of the narrow mud-weight window, Drilling Office integrated drilling software and VIRTUAL HYDRAULICS drilling fluid simulation software were used for tracing the well trajectory, performing torque and drag simulations, evaluating the rheology in terms of ECD management, and optimizing hole cleaning.

Demonstrate effective alternative to oil-based mud

An RSS was used to drill the well to minimize tortuosity. In consideration of the potential crude oil influx, a laboratory test was performed to determine the tolerable oil concentration for the 6 1/8-in section to help control rheology, ECD, and lubricant concentration. Based on the laboratory results, the ECD was controlled and held to less than 2.1 relative density. A computer simulation was used for determining the mud weight required to avoid tensile failure.

To maintain the ECD and enhance hole cleaning, fluid density was held constant, rheology was kept low, flow rate was held within a fixed range, weighted pill use was minimized, and low-gravity solids were kept at low values. Backreaming was not required for maintaining wellbore integrity.

Wintershall drilled the well—including its 3,281-ft lateral—to TD at 13,330-ft MD in 70 days. The drilling fluid system obtained excellent inhibition with no caving, swelling, or tight hole issues, even after the open hole was exposed for 33 days. In this underbalanced drilling application with oil influx to 8% contamination, the KLA-SHIELD system proved to be an excellent alternative to oil-based mud.

The low-viscosity pill helped to clean the bit, improving ROP after each pill run. Enhancing the KLA-SHIELD system with STARGLIDE lubricant and DRILZONE additive improved lubricity, resulting in an ROP increase to 22 ft/h [6.7 m/h] on average in the 6 1/8-in section. Running the casing was accomplished in 33.75 h.