A New Approach to Improve Cuttings Transport in Horizontal and Inclined Wells

Abstract

With increasing measured depths and horizontal displacements in extended reach (ERD) wells, good hole cleaning remains one of the major concerns in the oil and gas industry. While the methods currently used to increase cuttings transport capacity seek to increase the drag force applied to drilled cuttings, they are unable to significantly increase the cuttings transport capacity in horizontal and inclined wellbores because the gravitational force causes the cuttings to settle to the bottom side of the borehole. The proposed technology works to counteract the gravitational force while simultaneously increasing the drag force by attaching gas bubbles to drilled cutting particles with chemical surfactants. The gas bubbles will pull the cuttings upward because of their buoyancy in the drilling mud thereby counteracting the gravity force. Furthermore, the gas bubble/cutting aggregation will have a larger surface area than the cutting alone, resulting in an increase in the drag force. In addition to the theory behind this technology, this paper also focuses on laboratory development. Laboratory experiments were conducted to determine the effects of chemical surfactants, pH, and cutting particle size on the attachment of air bubbles to cutting particles. Two types of chemical surfactants, one to attach air bubbles to cutting particles and another to strengthen the air bubble, were necessary for attachment to occur. The corresponding chemical solution, with a pH range of 9 to 11, resulted in the optimal attachment of air bubbles to drilled cuttings up to 1.4mm in diameter that can be floated to the top of the fluid. Thereafter, experiments were conducted on a laboratory-scale flow loop with a horizontal test section. While conducting the flow loop experiments in the base solution without chemical surfactants, no cuttings were moved along the horizontal section. However, with the use of straight chain chemical surfactants up to 30% of the cuttings were carried completely across the horizontal tube by air bubbles and many other cuttings were carried partially across the horizontal tube. Further experiments showed that the use of certain branched chemical surfactants can greatly increase (about 58% of the cuttings were transported) the strength of attachment between air bubble and drilling cuttings compared to straight chain surfactants. These results show that this technology has the potential to make a "step-wise" improvement of cuttings transport capacity in horizontal and inclined wells. Introduction As the need for directional and horizontal wells increased, the interest in cuttings transport problems has shifted from vertical to inclined and horizontal geometries in the last 20 years. With increasing measured depths and horizontal displacements in extended reach (ERD) wells, good hole cleaning remains one of the major factors affecting cost, time, and quality of directional, horizontal, extended reach, and multilateral oil and gas wells. It has been recognized for many years that removal of cuttings from the wellbore during drilling of highly inclined and horizontal wells presents special problems. Poor hole cleaning can result in expensive drilling problems such as stuck pipe, lost circulation, slow drilling, high torque and drag, lost control of density, poor cement jobs, etc. If the situation is not handled properly, these problems can ultimately lead to the loss of a well. A single stuck pipe incident may cost over one million dollars. Combined stuck pipe costs for industry, was reported in the range of 100 to 500 million US dollars per year1. In attempts to avoid such problems, drilling operators often include such practices as "washing and reaming" wherein the drilling fluid is circulated and the drill string is rotated as the bit is introduced into the wellbore, and "back reaming" wherein the drilling fluid is circulated and the drill string is rotated as the bit is withdrawn from the wellbore. Other operations such as "wiper trips" or "pumping out of the hole" are often performed to attempt to control the amount of cuttings accumulated in the wellbore. All these operations require time and can significantly increase the cost of drilling a highly inclined or horizontal well. As a result, the search for more effective methods to improve directional and horizontal borehole cleaning is of great concern in the oil and gas industry.

Numerical modeling and simulation of drilling cutting transport in horizontal wells

“…Some of affective parameters on wellbore cleaning have been studied by some researchers experimentally (Tomren et al 1986;Yu et al 2004;Ford et al 1990;Hareland et al 1993;Okrajni and Azar 1986;Sifferman and Becker 1992;Hussaini and Azar 1983) and by modeling approach (Nguyen and Rahman 1998;Wazed 2002;Akhshik et al 2015;Zhu et al 2013). Tomren et al (1986) published the results of experimental studies with various drilling fluids in plastic pipe lines with inclination angle from 0° to 90°.…”

“…Although various affecting parameters on hole cleaning have been reported by some researchers during past decades (Tomren et al 1986;Yu et al 2004;Ford et al 1990;Hareland et al 1993;Okrajni and Azar 1986;Sifferman and Becker 1992;Hussaini and Azar 1983;Nguyen and Rahman 1998;Wazed 2002;Akhshik et al 2015;Zhu et al 2013), a comprehensive investigation of drilling fluid, cutting density, deposit ratio, string stress on the hole cleaning especially in horizontal wells has not been fully studied. Highlighting the contribution of the article, in this study various affecting parameters on hole cleaning in horizontal well by CFD simulator have been investigated and the results are verified with experimental data in literature.…”

Horizontal Drilling Well Proposal in West Qurna Oil Field (Iraqi Oil Field)

“…A new mathematical method for estimating the minimum fluid transport velocity for system with the inclination between 55° to 90°was developed by [4]. A study on improving cuttings transport capacity of drilling fluid in a horizontal wellbore by attaching air bubbles to the surface of drilled cuttings by using chemical surfactants was performed by [5]. The effects of hydraulic factors on cuttings transport and hole cleaning and analyzed data using experimental facilities in a 70 cm 5 m long flow using water and water solutions of Carboxy Methyl Cellulose (CMC) was studied by [6] .…”

Estimation of "Very-Difficult-to-Identify" Data for Hole Cleaning, Cuttings Transport and Pressure Drop Estimation in Directional and Horizontal Drilling

“…Becker, Azar and Okrajni (1991) conducted experimental study comparing the effects of fluid rheological parameters (fluid yield point (YP), plastic viscosity (PV), YP/PV ratio, power law exponent, consistency index, etc.) Yu et al (2004) proposed a new approach to improve the cuttings transport capacity of drilling fluid in horizontal and inclined wells by attaching gas bubbles to the surface of drilled cuttings using chemical surfactants. They pointed out that turbulent flow improved cuttings transport for highly-inclined wellbores, and the effects of fluid rheology dominated at low inclinations.…”