Owing to the high depletion and narrow drilling windows characteristic of many wells in the South China Sea, the risks of severe losses increase exponentially. Mud density, sufficient to maintain well control, typically exceeds the fracture gradient of the clastic and coal formations. Thus, operators face a dilemma in balancing the need for mud weight to remain below the fracture gradient to avoid losses, while also providing sufficient density to block influxes into the well.
This paper describes the development and application of a process that essentially stabilized troublesome zones and enabled the wells to be drilled with mud weights higher than the maximum density. The authors will describe the drilling process that stabilizes microfractures in the formations and mitigates many of the issues associated with wellbore instability. The presentation of a case history will illustrate the historical mud weights and properties used to drill offset wells, and the corresponding hole stability problems. The comparative analysis demonstrates how the use of a higher mud weight eliminated well influxes while simultaneously achieving zero mud losses to the formation.
Furthermore, the technology delivered additional wellbore strength to weak formations, allowing the drilling operation to be completed as per plan. Accordingly, the operator significantly reduced the wellbore stability challenges associated with lost circulation, stuck pipe and well instability, thereby facilitating easier logging and delivering a quality, and less costly, producing well.