Abstract
With rising energy demand, operators in the Middle East are now focusing on developing unconventional resources. To optimize hydraulic fracture stimulation, most of these deep gas wells are required to be drilled laterally and in the direction of the minimum horizontal stress. However, this poses an increased risk of stuck pipe due to hole instability, differential sticking and skin damage due to high overbalance pressures, which makes drilling these wells challenging and costly. Another major challenge in the Middle East is lost circulation due to natural fractures in carbonate reservoirs. Lost circulation currently accounts for loss of approximately $850-900 million USD per year globally across the industry (Marinescu 2014).
This paper presents a case study where a holistic approach; combining geomechanics and drilling technologies were employed to address the drilling challenges specific to unconventional and naturally fractured reservoirs. Ultimately, this approach helped the client to mitigate stuck pipe issues, while proposing a physics/engineering-basedmethodology to reduce losses by sealing fractures, hence providing a roadmap to optimized drilling and mitigation of hazards with associated Non-Productive Time (NPT).
The paper demonstrates a holistic approach, combining wellbore stability analysis, managed pressure drilling (MPD) and proposes a novel physics/engineering-based methodology for addressing lost circulation challenges. A 1-D wellbore stability model is initially developed to determine the safe operating downhole pressure limits and to effectively assess the drilling risks associated with the planned wellbore orientation. By accurately determining the required bottomhole pressure to prevent wellbore stability problems, managed pressure drilling technology can be implemented to provide improved drilling hazard mitigation by enabling reduced overbalance pressures, constant bottomhole pressure, and faster reaction time by instantaneously adjusting downhole pressures. A bi-particulate bio-degradable system is used as a lost circulation material (LCM). The bigger size cylindrical particles flowing at a pre-defined rate will form a bridge or a plug across the fracture aperture, providing mechanical stability and the smaller spherical particles will seal the gaps in the bridge there by providing an effective sealing of the fracture opening.
From experience, implementing these methodologies and technologies in isolation has not provided satisfactory results. This indicates that a partnership which leverages the strengths of the individual disciplines from the early planning stages is necessary to effectively address the drilling challenges posed by unconventional and naturally fractured reservoirs. For the case study highlighted in this paper, the well was drilled to TD in a timely manner, while maintaining the integrity of the hole, hence confirming the viability of this approach. In addition, the physics and engineering design workflow for bi-particulate bio-degradable LCM demonstrates how it can be effectively deployed to mitigate lost circulation without skin damage to the formation
Drilling Fluid and Cement Slurry Design for Naturally Fractured Reservoirs