ABSTRACT:

Drilling depleted zones has become a frequent and familiar scenario for numerous wells today. Wellbore instability and formation damage, which can be encountered during drilling of weak formations and depleted reservoirs, have become major concerns for operators who want cost-effective, safe and timely delivery of their prospects. With the drive to maximize returns in many fields and extract all available hydrocarbons from reservoirs, drilling depleted zones is costing the industry millions of dollars every year. It is generally agreed that the solution to these problems is a combination of drilling fluid optimization and good drilling practices. The design and optimization of drilling fluids for depleted zones needs to address the following problems which often are encountered while drilling such formations:

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    Wellbore stability

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    Natural and induced fractures

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    Matrix fluid loss

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    Differential sticking

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    Productivity optimization

Associated with each of these areas are traditional as well as novel laboratory methods that help determine the most effective fluid formulation and drilling practices for optimizing the drilling operation. This paper deals with the design of optimum fluids for depleted zone drilling and the testing protocol that is required to validate their performance prior to field application

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