Evaluating the effect of mud rheology and cuttings size on cuttings transportation in vertical wells

As drilling optimization becomes the major concern of the drilling engineer and the mud specialist, there is therefore need to properly evaluate key success factors that ultimately affects the success of drilling operations. This research work examined the effects of fluid rheology and cuttings size on cuttings transportation in vertical wells. To achieve that, an experiment was conducted on two samples of fresh oil-based mud (A and B) of different rheology and two drilled cuttings sample (A and B) of sizes 400µm and 1000µm obtained from Anieze North field after sieve analysis. The drilled cuttings samples(A and B) were comingled with the mud(A and B) and their rheology (viscosity, density, plastic viscosity, yield point and gel strength) and cuttings transport parameters (slip velocity, transport velocity, transport ratio and transport efficiency) were checked at different temperatures. The cuttings transport parameters generated with the test models (Moore, Chien et al, and Zeidler) reveal that drilled cuttings of smaller size are easily transported than those of larger size. It was also observed that temperature has remarkable effects on rheology and slip velocity. Hence, slip velocity increases with temperature, while rheological values decrease with temperature. As a recommendation arising from the results of this investigation, a lower cuttings size should be ensured in a low viscous fluid for an efficient hole-cleaning. Apart from the aforementioned factors for efficient transportation of drilled cuttings, drilling bit configuration which is major determinant of the size of cuttings should be properly examined before selection for any drilling operation. Keywords: Cuttings Size, Cuttings Transport, Mud Rheology, Slip Velocity, Temperature