Foam rheology characterization as a tool for predicting pressures while drilling offshore wells in UBD conditions

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Foam rheology characterization as a tool for predicting pressures while drilling offshore wells in UBD conditions

Martins, A.L. / Lourenco, A.M.F. / Sa, C.H.M. / Silva, V. jun.

The use of foam is a highly attractive alternative for drilling depleted, loss circulation or gas zones. Due to its complexity, a foamed system requires special attention while designing field operations. This paper summarizes an extensive experimental program developed at PETROBRAS R&D Center facilities, coupled with a set of real scale tests under foam circulation conditions and numerical simulations, aiming the development of a comprehensive and useful model for predicting bore hole pressures while drilling under-balanced or near balance with foams. The lab work steps include foaming agent selection, rheology lab equipment development and/or adaptation, definition of test procedure and matrix, besides discussion and analysis of results. After about 60 rheology tests performed in several lab and pilot scale equipment, correlations were proposed to predict rheological parameters as functions of foam quality. Based on the experimental data, a set of correlations was developed to predict foam rheological properties as functions of base fluid rheological properties and foam quality. The next step was to evaluate the lab results by comparing pressure predictions with experimental data obtained by circulating different quality foams in a real scale vertical well located at PETROBRAS Training Center. The proper fitting of the proposed model and the experimental results supported its implementation in PETROBRAS lightweight fluid drilling software.