A novel concept for cleanup prediction during sampling is proposed. This concept shifts focus to the early phase of cleanup, allowing for early predictions of pumpout time or produced volume using optical fluid analysis logs versus given contamination targets. The early phase of cleanup potentially provides a great deal of information to be used in prediction of cleanup, because this phase is strongly affected by both the local flow pattern and the contamination transport and deals with a larger range of optical density variation.
A new approach to cleanup prediction is based on a truly 3D model of flow and contamination transport to the probe production area at the wellbore wall covered by mudcake. This model better captures the initial phase of cleanup than the conventional spherical flow model, which incorporates axisymmetrical contamination transport to a small production sphere located at the wellbore axis.
The new model provides the signature of 3D contamination transport on cleanup dynamics, which is controlled by the ratio of invasion depth to wellbore radius. The analysis of new problem solutions reveals new details of cleanup evolution. In particular, the transition from a predominantly circumferential regime of cleanup to a predominantly vertical cleanup has a distinctive signature that can be used in cleanup progress monitoring and the reconstruction of initial invasion depth.
Examples of sampling job data processing that support the new concept are provided. They indicate that decent estimates of pumpout volumes can be obtained 3 to 5 times earlier using the new approach.