(85b) Gel Influence On Transient Pressure In Annular Flows

Formation of a gel structure is essential for good drilling fluid performance.  It is necessary for proper hole cleaning and for suspension of weight materials and cuttings removal from the hole.  However, the formation of a microstructure also results in transient pressure spikes when the gel structure is broken down, such as during pump initiation and tripping pipe, which can be severe and limiting in operations like managed pressure drilling (MPD).  There is a general understanding as how to the breakdown and resulting over-pressure are influenced by mechanical (annular size, pump speeds) and chemical (hydrophilic and organophilic clay interactions, emulsion droplets interaction, colloidal/fines loading) controls.  The future success of critical operations such as MPD depends on a better understanding of how the gel structure breakdown occurs and modeling which allows incorporation into existing well design programs.

This paper presents new models for evaluation of gel breakdown in a variety of drilling fluids.  This model allows for the recognition of mechanical effects observed in the breakdown and for potential modeling of multiple modes of microstructural bond breakage.  By comparison of the decay constants included in this model, differences between mud types can be illuminated.  The effects on transient pressures predicted with the inclusion of this model are also presented.