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

Abstract

This paper presents the finds to date of a research project initiated to investigate drilled cuttings project initiated to investigate drilled cuttings transport in deviated wellbores. The research programme utilizes a simulated wellbore to study the programme utilizes 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 m 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 miniinum 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 regiine appear to have highest impcct 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 appears 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 predicted MTV from the computer model concurrently being developed and good agreement has been observed.Introduction. One of the primary functions of the drilling mud is the efficient transportation of cuttings to the surface, a function that depends largely on the fluid velocity and other parameters such as the fluid rheological properties, cuttings size, etc. properties, cuttings size, etc. However, over the years, it has been found that the well geometry can also have a strong influence on the hole cleaning efficiency and the question arises as to how to adjust the fluid properties and circulation rates to suit the fixed design parameters such as hole angle, pipe eccentricity, etc, in order to ensure optimum pipe eccentricity, etc, in order to ensure optimum hole cleaning efficiency.In the first major study published on cuttings transport, Piggot identified the parameters affecting mud carrying capacity. Williams et al subsequently reported on a series of laboratory and field experiments, and were the first to try and determine the minimum annular velocity necessary to remove cuttings from the hole. They invariably highlighted the various factors that affect the efficiency of cuttings transport which have also been reported by other researchers.