Novel Wellbore Strengthening Enables Drilling of Exploration Well in a Highly Depleted Formation

Abstract

Abstract Operators all over the world are still facing the challenge of having to drill through highly pressure depleted formations in order to drill to lower lying hydrocarbon bearing zones especially in terms of wellbore stability and loss circulation. Stability of boreholes in these scenarios requires a careful consideration of in-situ stresses, rock strength, pore pressure, wellbore fluid pressure and drilling fluid characteristics. Managing lost circulation with stability offormations is one of the most difficult scenarios that needs proper engineering. Before a depleted zone can be cased-off, it has to be successfully drilled. Drilling through highly depleted sands can result in problems such as lost circulation, differential sticking, difficult logging and/or not being able to reach the well objective depth, wellbore instability resulting in significant and expensive non-productive time (NPT) and costly remediation process, in addition to the loss of costly mineral oil-based mud used for drilling. Remedies such as squeezes, cement plugs, expandable liner and casing while drilling can be costly solutions and are not always successful. Key factors in the successful drilling of study wells included special drilling fluid design, rock mechanics study, pro-active use of bore hole strengthening technology, integration of supplier and operator expertise, and excellent communication between all parties involved. The study showed that enhanced formation strength can allow sufficient tolerance to overbalance pressure leading to the use of higher mud weight due to the widening of mud weight window especially when an exploration objective is to be drilled below depleted formations. This paper presents the result of the use of a novel system used in improving the formation strength characteristics in a depleted environment.