In recent times, the oil industry has shown increasing awareness towards maintaining optimum well productivity through better HP-HT drilling/completion fluids design. However, the mechanisms of drilling fluid filtration and impact on productivity performance are not well understood, especially in an HP-HT environment.

In open hole completions the productivity losses are critical because the near-wellbore damage is not by-passed by perforations.

Furthermore, a satisfactory model for field applications to simulate the near-wellbore damage in terms of well flow performance from laboratory core test analysis still is not available.

In this paper, the results of in-depth experimental research into rheology, filtration and formation damage phenomena and the relationships between them. The experimental data combined with data analysis of static and dynamic filtration models provided the database for the semi-empirical mechanistic models that were developed. These models have been combined and incorporated into a design and evaluation tool - the productivity tool, for predicting the effect of HP-HT drilling fluid filtration on formation productivity.

A number of results have been presented to illustrate how the new tool can be used to evaluate the damage factor of a given fluid, specify the invaded zone skin as well as the depth of invasion, two key parameters that are useful and relevant to optimum fluid selection and management in addition to well test data interpretation.

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