Wells drilled in the direction of minimum stress are potentially more favorable for reservoir development and optimal production. In such a situation, hydraulic fractures grow transversely to the wellbore axis, allowing placement of multiple fractures without the overlapping fractures. However, wells that have been drilled in the minimum horizontal stress direction typically encounter drilling-related problems such as stuck pipe, wellbore breakout and lost circulation. These problems can result in increased well costs due to significant periods of non-productive time and in the worst case, loss of the well.
To address this, wellbore strengthening techniques can be applied to bridge or plug fractures and increase near-wellbore stability via hoop stresses. Designing drilling fluids from a wellbore strengthening point of view has proved successful at managing problems associated with wells that have high overbalance pressure and low formation strength. As more challenging wells are drilled, though, overbalance pressures are exceeding the wellbore strengthening capabilities of existing fluid designs. These high-overbalance pressures significantly increase the risks associated with drilling in the minimum stress direction.
This paper describes an improved, environmentally acceptable, customized high-performance system that can be used in water-based and oil-based mud systems, enabling wells to be drilled with more than 4500 psi overbalance pressure and mud weights beyond 145 pcf. This newly designed system helps the operator increase operational efficiency by:
Minimizing the risk of differential sticking
Reducing downhole losses
Improving wellbore stability
Reducing torque and drag through enhanced lubricity
Laboratory data is presented outlining the design of the new system and field case studies show how this new, improved bridging system reduces the risks associated with drilling in the minimum stress direction through highly depleted reservoirs or reservoir sections where multiple targets may be separated by high-pressure zones that require higher mud weights.