Cleanup of an extended reach horizontal well with maximum reservoir contact is challenging especially when a large amount of mud is lost into the reservoir formation. During the well cleanup operation, not only the existing completion fluid needs to be unloaded from the wellbore, but also the drilling fluid that invaded into the formation needs to be back-flowed to minimize formation damage and regain well's capacity.

This paper describes the successful application of a mechanistic wellbore model coupled with a near wellbore dynamic reservoir simulation model to history match clean-up operation of a maximum reservoir contact (MRC) well. The coupled model was simulated for a sequence of events starting from mud loss during a stuck liner incident, followed by subsequent well cleanup using coiled tubing unit (CTU) with nitrogen to recover large amount of drilling mud invaded into the pay zone, to PLT run along the long lateral for assessing flow profile. The PLT flow profile was used to calibrate the reservoir model in terms of skin factor, matrix and relative permeability.

Given the transient flow nature of well unloading operation, the coupled model is best suited to simulate oil and mud movement from reservoir through porous media, into the wellbore together with nitrogen, and then being lifted to the surface with the changes in PVT properties (density, viscosity, solution GOR). The coupled transient multi-phase flow model is able to achieve good history match on mud invasion into the wellbore reservoir region, thus providing good insight on the key operational and reservoir parameters influencing cleanup efficiency. The tuned model predicts the total cumulative liquid, oil and water phase volumes with fair accuracy. This study shows the importance of transient dynamic simulation in history matching and predicting well cleanup and the recovery of the invaded mud from the formation. The key benefit from the study is that the model is a very useful tool for designing the most economical and efficient cleanup operation in terms of total operational/rig time, injectant selection and the volume, as well as the operating parameters.