Advancement in High Performance Water Based Mud (HPWBM) coupled with a deeper understanding of shale and chemical interaction has taken a leap in recent years enabling the drilling of challenging wells whilst replacing Synthetic Based Mud (SBM) as the preferred technical option. The exceptional inhibition properties, versatility to chemical manipulation and stability, as well as being an environmentally beneficial alternative to SBM, HPWBM has proven to be a robust solution for drilling the challenging Muderong shale and highly depleted reservoir sands in the field.
Through a detailed field wide offset review focusing on wellbore stability and shale reactivity relationship observations, time dependent shale reactivity and an engineered bridging package was the basis of a successful fluid formulation and selection which then resulted in a flawless execution of the challenging well. Various testing of shale cuttings from the field paired with an offset review was key to understanding the extent of shale reactivity in relation to the type of shale being drilled and cause of shale instability in the area. These results were imperative in providing technical justification to utilise HPWBM for drilling through the Muderong shale. Applying detailed reservoir drilling fluid analysis to the overburden drilling fluids design and incorporating previous offset fluid design learnings, provided a robust and versatile drilling fluid system.
This paper will review the steps undertaken to validate the selection of HPWBM over SBM through detailed analysis of wellbore stability, shale reactivity, permeability assessment, pore throat sizing and pore pressure transmission. It will present the misnomer of comingling the wellbore stability requirement, primarily mud weight, with shale reactivity in the field as well as the relation between the plateauing of shale reactivity curves to near well wellbore swelling. Extensive laboratory testing was performed to formulate and demonstrate the efficacy of the bridging package in addressing differential sticking, losses and wellbore strengthening in highly depleted sands. In addition, this paper will also present actual field results on stability of the fluid properties along with resultant torque and drag throughout drilling of a directional well with no requirement for lubricants.
This paper should be of interest to all engineers and technologists who are involved in shale reactivity analysis, well design, drilling fluids design, selection and interaction as well as highly depleted reservoir sand drilling.