A Novel Approach to Determining Carrying Capacity Index Through Incorporation of Hole Size and Pipe Rotation

Abstract

Current API RP13D guidelines outline 3 methods for determining hole-cleaning efficiency based on wellbore angle. Method 1, used in low-angle wellbores (<30°) compares cuttings slip velocity with annular velocity to determine a transport ratio and cuttings concentration. Method 2, also used for low-angle wellbores (<30°) derives a carrying capacity index (CCI) based on bulk annular velocity, fluid density and power-law rheology. Method 3, used in high-angle wellbores (<30°) derives a transport index (TI) based on fluid rheology, density, and flow rate. TI is then plotted on an empirically derived chart (Luo et al., 1992, 1994) to determine maximum allowable rate of penetration (ROP) that should ensure efficient hole cleaning. Although these methods are considered recommended practices by API, Method 3 (TI) is based on an outdated study (Luo et al., 1992) with limited scope (one flow loop, one field test). Additionally, this method neglects the importance of drill pipe rotation and pipe eccentricity in cuttings transport efficiency, which has been proven to be a factor in other studies (Akhshik et al., 2015; Sanchez et al., 1997b). This paper highlights the shortcomings of current API standards and identifies what effects contributing factors such as pipe eccentricity and drill pipe rotation rates may have on cuttings transport efficiency. Further, this paper discusses the impact pipe-to-hole area ratio and wellbore flow area have on the effects of drill pipe rotation and flow channeling. Five horizontal wellbores were modeled using Siemens Star CCM+ Computational Fluid Dynamics (CFD) software, with bottom-eccentric 4 ½″ drill pipe placement, in annular diameters of 6¾″, 7 ⅞″, 8 ⅜″ 8 ½″ and 8 ⅝″. Additionally, one bottom-eccentric 5″ drill pipe in an 8 ¾" wellbore was modeled to compare identical pipe-to-hole area ratios with different flow areas. Simulations were run with drill pipe rotation speeds increasing from 0 to 180 RPM, in 30 RPM increments. In order to determine the impact fluid rheology has on flow channel development, both medium density oil-based muds and light density water-based muds were modeled and compared. Bulk annular flow velocity was set to 100 ft/min, to maximize the observable effects of drill pipe rotation. Bulk average velocity was calculated from cross sectional area, determining both annular velocity (velocity parallel to wellbore) and absolute velocity (fluid velocity magnitude regardless of direction). The resultant velocity profiles were used as the annular velocity component in API CCI and TI calculations and compared to bulk annular velocity. In addition to observing fluid velocity for CCI and TI calculations, changes in effective viscosity from the onset of pipe rotation was also analyzed to determine changes in wellbore parameters that may affect cuttings transport.

A Novel Automated Model for Evaluation of the Efficiency of Hole Cleaning Conditions during Drilling Operations

“…However, as the zenith angle increases, the reduc in the final settling velocity contributes less and less to the cleaning quality (Figure The sludge transport efficiency has to be corrected, because only the axial componen the final settling velocity is taken into account. It is therefore more difficult to predict cleaning quality in such cases [22]. When predicting and controlling well cleaning, formation of cutting layers has to be taken into account.…”

A Novel Efficient Borehole Cleaning Model for Optimizing Drilling Performance in Real Time

“…where the variable CCA represents the cuttings concentration in an annulus, and it is defined by Equation ( 4) [8,40].…”

A Novel Model for the Real-Time Evaluation of Hole-Cleaning Conditions with Case Studies

“…Rathgeber (2023) examined the impact of pipe eccentricity, drill pipe rotation rates, pipe-to-hole area ratio, and wellbore flow area on cutting transport efficiency. The author additionally examined the influence of the ratio between the area of the pipe and the hole, as well as the area of flow within the wellbore, on the rotation of the drill pipe and the occurrence of flow channeling [55]. Moreover, Tables 1 and 2 show a summary of major findings for other studies related to hole-cleaning chemistry and engineering.…”

“…An equivalent mud weight (EMW) that incorporates the cutting accumulation (CA) is presented by Equation ( 15), based on [2,55,86].…”