Gel Strength as Related to Carrying Capacity of Drilling Fluids

Abstract

This paper was presented by an SPE Program Committee following review of Information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the or SPE, their officers, or members. Papers presented at SPE meetings are subject to publication review by editorial Committees of the IADC and SPE. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Write Publications Manager, SPE, P.O. Box 833838, Richardson, TX 75083-3836 U.S.A. Telex, 730989 SPEDAL. Abstract It is known that the plastic Bingham model is inadequate to represent some types of drilling fluids, such as low solids and emulsions, especially at medium and low shear rates. Previous experiments on carrying capacity concluded that the average annular velocity and rheological properties affect the fluid transport more significantly than other parameters. Many of these experiments refer to the yield point of the Bingham model, calculated at high shear rates as the most important parameter. This experiment studies how the initial gel strength and plastic yield point affect the carrying capacity of the drilling fluids employing the transport ratio concept. For this purpose the terminal settling velocity of the drilled solids through quiescent fluids was experimentally determined. The results showed a better correlation with the initial gel strength than with the yield point. Also, the analysis of the results demonstrated that a gel strength of about 1.92 Pa (4.0 lbf/100 ft2) is necessary and substantial to obtain a transport ratio higher than 0.50 when the annular velocity is in the range of 0.41 m/s (80 ft/min) to 0.66 m/s (130 ft/min), using low solids and polymer drilling fluids. For any type of water based drilling fluids a gel strength in the range of 3.35 Pa (7 lbf/100 ft2) to 4.79 Pa (9.0 lbf/100 ft2) is sufficient to remove the cuttings at more than 0.50 of transport ratio, even when the annular velocity is about 0.25 m/s *50 ft/min). Introduction The transport of drilled solids from the bottom hole to the surface, throughout the annulus, is one of the main objectives of the drilling fluids. The terms removal velocity and transport ratio are often used to estimate the ability of a drilling fluid to transport drilled solids in a vertical well. The removal velocity is a mean value of the relative cuttings velocity which is equal to the difference between the average annular fluid velocity and the ave rage slip velocity of the cuttings. (1) Vr = Va − Vs The average annulus velocity is defined as a function of the flow rate and the dimensions of the annulus, while the slip velocity is defined as the average velocity at which the particles tend to settle in a fluid. This velocity depends on the size of the particle, its geometry, its density, and properties of the fluid, mainly rheological and density. The transport ratio is defined as follows: (2) Va Vr = Rt = = 1 − ( Vs Va ) The analysis of the equation (2) shows that the transport ratio increases when the slip velocity decreases or the annular velocity increases. If the slip velocity is equal to zero, then the transport ratio will be transported with the same annular velocity. Conversely, if the slip velocity is high the transport ratio will be low. In this case, note that the concentration of the solid in the annulus will increases.

Rheological and filtration property evaluations of the nano-based muds for drilling applications in low temperature environments

“…As indicated in the graph, the low gel strengths observed from the Mud-2 especially at high temperatures were caused by the presence of salt ions in the mud suspension reducing the hydration capacity of the clay mineral. With the addition of alumina nanoparticle as low as 0.05 wt%, significant improvements were observed on both 10-second and 10-minute gel strengths to the more acceptable range to provide good carrying ability, i.e., 5 Pa as suggested by Machado et al, 1990. An increasing trend was also observed as the concentration of alumina increases.…”

“…In the field, they represent the shear stress required to breakdown the gel structure of the mud to restart the flow. They are Machado and Aragao, 1990, suggested that a gel strength of about 5 Pa is sufficient to suspend cutting and provide good carrying capacity. Low and flat gels over time are always favourable as they indicate a constant rate of gelation.…”

Synergistic Effects of Ionic Characteristics of Surfactants on Aqueous Foam Stability, Gel Strength, and Rheology in the Presence of Neutral Polymer

“…However, excess values can cause pipe-sticking problems. Hence, optimization of the gel strength is essential for the design of a drilling fluid …”

A new method for determining the minimum gas injection rate required for hole cleaning in horizontal gas drilling

“…In drilling horizontal well with gas, the suspension of a cutting is mainly due to three forces: one acts downward due to gravity, another lifts upward due to buoyancy, and the third lifts upward again due to viscous friction around the particle in the vertical direction (Machado and Aragao, 1990).…”