Drilling Fluid Sweeps: Their Evaluation, Timing, and Applications

Abstract

Drilling fluid sweeps are commonly run in the field to help clean the borehole of cuttings that have not been removed with normal fluid circulation. Typically, these sweeps are used in vertical and deviated drilling operations. In high angle or extended reach wells, their use can be helpful in removing cuttings that have accumulated in sections where hole cleaning is not optimized. Sweep types usually fall into the following categories:High-viscosityHigh-densityLow-viscosityCombinations of any 2 of the aboveTandem (one type followed by another) Their effectiveness in the field is often quite spotty, often due to the application of a certain sweep type in the wrong drilling situation. Heretofore, there has been lacking a rigorous method of evaluating the effectiveness of sweeps at the rig site. Usually sweeps have been evaluated in the field based on observed or perceived quantities of cuttings coming over the shakers, a methodology that can be very subjective. In this paper, a rigorous method of evaluating drilling fluids sweep efficiency is proposed. Here, information from pressure-while-drilling (PWD) tools and measured drilling fluid and sweep fluid properties is used to determine a mathematical prediction of "cuttings out". In short, the method relies on the difference between "mass in" and "mass out". Examples from field applications are given to illustrate the usefulness of this methodology. With a more rigorous evaluation of drilling fluid sweep efficiency in hand, users can objectively determine the type and frequency of application of drilling fluid sweeps and rig time spent circulating out ineffective sweeps can be minimized. Introduction Drilling fluid sweeps are usually applied in wells to augment hole cleaning, especially in high-angle or extended-reach wells where efficient hole cleaning is more difficult to maintain than in vertical or near-vertical wells. In the deviated wells, the drilled cuttings can accumulate on the lower side of the hole at angles greater than 35–40° from vertical. If left unattended, this accumulation can become severe enough to lead to hole pack-offs, stuck pipe, and other unwanted incidents of non-productive time. Drilling fluid sweeps are formulated to achieve certain properties that provide additional lift to cuttings in vertical and near-vertical wellbores. In high-angle wells, drilling fluid sweeps can be used to scour the top layers of drilled cuttings accumulation and to displace lighter-density areas of the annulus where drilled cuttings accumulation is thought to occur. There is not much information pertaining to use of drilling fluid sweeps that is available in the literature, a sign that this particular area of investigation has not received much attention among drilling fluids researchers. In a recent paper1, the authors described various types of sweeps and provided field evidence to support improved cleaning with changes in downhole measurements of annular pressure (PWD). In addition, the authors made extensive use of computer modeling to gauge drilling fluid sweep performance. A common problem associated with this approach involves the inherent assumptions implicit in the modeling process. It would be much better to use actual drilling and drilling fluid parameters to gauge hole cleaning improvement with use of drilling fluid sweeps. The use of drilling fluid sweeps having a density higher than the drilling fluid system itself to improve cuttings transport is the subject of a U.S. Patent2. In this patent, small volumes of drilling fluid commonly weighted up with specially-sized barite particles were used in deviated wellbores, and the changes in ECD and hole cleaning efficiency were described. Again, any advantages using these sweeps in removing cuttings from the wellbore were only qualitatively described and / or modeled.

Review of Hole Cleaning in Complex Structural Wells

“…Some field applications were also conducted, and made some achievements [28,29]. However, the flow behavior, hydraulics, and cuttings-transport efficiency of fiber sweeps is less known, and some experiments [8][9][10] about fiber sweep were conducted.…”

Stability and Flow Behavior of Fiber-Containing Drilling Sweeps

“…Considering these factors, the easiest and most economical procedures to improve hole cleaning involve increasing annular velocity preferably into the turbulent flow regime or using sweeps of higher density or viscosity than the drilling fluid. Sweeps are commonly categorized as i) high-viscosity; ii) high-density; iii) low-viscosity; iv) combination; and v) tandem sweeps (Hemphill, 2002). Sweeps provide a number of benefits such as reducing cuttings beds -thus decreasing annular pressure loss -and reducing torque and drag at the surface.…”

Fiber Sweeps for Hole Cleaning

“…In highly inclined and horizontal wells, drilling-fluid sweeps can be applied to reduce cuttings-bed thickness. Conventional drillingfluid sweeps are classified into high-viscosity sweeps, high-density sweeps, low-viscosity sweeps, combination sweeps, and tandem sweeps (Hemphill and Rojas 2002).…”