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When the invasion of drilling, completion and workover fluids is reduced to as low a level as possible, problems with mechanically unstable formations, differential sticking and lost circulation are also greatly reduced. If invasion never occurs, or is stopped by the rapid formation of a seal, then rock mechanics considerations tell us that this is a viable route to wellbore strengthening. A properly formulated ultra-low invasion fluid (ULIF) will also reduce formation damage and so improve the prospects for optimum well productivity.
We describe the technology used to produce a class of ULIF and review the benefits that limiting fluid and pressure invasion brings to rock integrity, drilling performance and well productivity.
The paper then focuses on case histories. Log data are used to demonstrate that the ULIF reduces wellbore instability and fluid invasion. Evidence of wellbore strengthening is presented and the economic benefits of using ULIF are discussed.