Drill-Cutting Removal in a Horizontal Wellbore for Cementing

Abstract

Abstract For effective zonal isolation, drill cuttings and gelled, dehydrated drilling fluid (GDDF) should be removed from the wellbore before a cement job, but such removal can be a challenge when the wellbore is deviated and the casing is not centered. This paper discusses simulated wellbore experiments that investigated the effect of different factors on the removal of drill cuttings and GDDF from a horizontal well bore. The parameters studied included eccentricity, flow rate, hole size, casing size, fluids pumped as flush/spacer, and pipe movement. The results showed that below a certain flow rate, the drill cuttings and GDDF could not be dislodged from the wellbore. In field applications, this flow rate must be known so that job designers can selectively design flushes that will effectively dislodge the drill cuttings and GDDF. As expected, eccentricity also alters the velocity profile in the narrow side of the annulus, and geometry was also a factor in removal efficiency. The experimental setup, procedure, and results are discussed in detail. Flow rates needed to dislodge the drill cuttings and GDDF are also discussed, A numerical analysis of the fluid flow in wide and narrow annuli was also performed. Introduction Cement operators should always use the following guidelines to obtain a successful cementing job.Remove the drill cuttings.Remove the gelled and partially dehydrated drilling fluid. In some cases. this fluid will have the consistency of a paste. Hereafter, it will be referred to as partially dehydrated paste (PDP).Design the cement slurry to meet properties such as pumping time, fluid loss, gas migration, etc. In addition, design the density, rheology, and other placement parameters so that the cement slurry will displace the fluid ahead of it and seal the entire annulus. The cement formulation should also provide zonal isolation over the life of the well. The removal of drill cuttings and PDP are influenced by the following:–properties of drilling fluid, fluid loss, plastic viscosity etc, a temperature, pressure, differential pressure across the formation–shutdown period–drilling fluid formulation–wellbore details–casing/drillpipe size–hole size–standoff/eccentricity–pore pressure–fracture gradient For successful PDP removal, the downhole forces in both the narrow and wide sides of the annulus must exceed the yield stress of the PDP under downhole conditions. The force exerted could depend on the following factors:–flow rate of fluid–standoff/eccentricity–properties of fluid–pipe movement–wellbore geometry–scratchers Although the general effect of these parameters on a cement job is well known, the designer must quantify the effect of each factor to optimize the design of each individual well. For a wellbore with a certain drilling fluid, geometry and standoff, it may be difficult to generate needed forces by hydraulic means only. In such cases, ways to reduce the downhole forces should be explored. P. 347