Comprehensive Experimental Investigation of Drilled Cuttings Transport In Inclined Wells Including the Effects of Rotation and Eccentricity

Abstract

ABSTRACT This paper presents the findings to date of a research project initiated to investigate drilled cuttings transport in deviated wellbores. The research programme utilises a simulated wellbore to study the mechanisms of cuttings transport in deviated wells. The cuttings transport column, has been designed to allow easy variation of well geometry in terms of annular size, deviation angle and pipe eccentricity. The column is also equipped with a variable speed motor/gear system for the simulation of drillpipe rotation. This study has investigated the influence of a range of variables such as hole angle, fluid rheology, cuttings size, drillpipe eccentricity, circulation rate, annular size, and pipe rotation on cuttings transport efficiency using the concept of Minimum Transport Velocity (MTV). This concept presumes that a hole can be efficiently cleaned by either maintaining cuttings rolling or in suspension, if the annular velocity is equal to or greater than a minimum transport velocity for that operational condition. Thus, the lower the minimum transport velocity the easier it is to efficiently clean the hole. The results so far have shown that depending on the level of eccentricity and annular size, fluid rheology as well as flow regime appear to have highest impact on the MTV. With low viscosity circulating fluid, turbulent flow regime seems to predominate for concentric pipes with suspension and rolling attained at low MTV. The use of high viscosity fluids appeared to improve the cuttings transport further especially at highly deviated angles. The transport efficiency is further enhanced by pipe rotation at various levels of eccentricity. Smaller cuttings appeared to be easier to remove than larger ones. There is however a small exception to this when larger cuttings were found to be much easier to remove at low angles with the use of high viscosity fluids. The experimental results have been compared with the predicted MTV from the computer model concurrently being developed and good agreement has been observed.