HOUSTON TX.–Since drilling operations first began, operators have sought to reduce costs and the nonproductive time (NPT) associated with downhole tool failures. Yet, many bottom-hole assembly issues are caused by debris accumulated during the drilling cycle which can be challenging as operators strive to keep the bit on-bottom and drill ahead for the longest possible time.
For economic reasons, drillers routinely reuse oil-based drilling fluids from previous wells. However, surface drilling waste management equipment–such as shakers, centrifuges, desanders and ditch magnets–not always succeed in removing debris carried in the circulating fluid system. The debris buildup in rotary steerable systems (RSS) and directional BHAs can compromise steering capability and the accuracy of logging-while-drilling and measurement-while-drilling tools.
In addition, the use of standard filtering systems, can result in the small internal filters on directional drilling equipment becoming clogged. This often requires the operator to pull out of the hole to repair or replace equipment, leading to NPT.
Traditionally a wellbore cleanout run is performed to validate cleanliness and remove debris prior to well completion. However, interception and removal of both ferrous and nonferrous debris can now be done while drilling, with the added benefit of preventing the debris from damaging the drilling BHA.
The industry’s focus on improving drilling efficiencies and well economics in recent years has driven a change from a traditional debris management model; dedicated precompletion cleanout runs are now less favored as operators look to shorten the time required to deliver a well to production. Drawing on 25 years of lessons learned and technological expertise, a new strategy has been introduced that utilizes a range of drilling tools developed specifically to intercept debris and reduce the number of trips. The aim was to extend the service life of BHA equipment on each run to achieve more footage drilled before pulling out of the hole.
The strategy required engineering two new broad-application debris management technologies that can be used separately, or in tandem, to maximize debris capture from the well: a work string filter system and an open-hole magnet.
Double-Screen Filter
Introduced last year, the double-screen filter is designed to protect equipment from debris trapped in the circulating system. Applicable in any drilling environment and mud type, the slick sub tool is incorporated in the drill string and positioned directly above the BHA, where it captures and retains all fluid-borne nonferrous debris in the drill string before it can compromise BHA components using an impeller, modulator or pulsar.
The filter features a variable-slot size and a double (one inside the other) screen configuration engineered to reduce high fluid velocity, which causes premature filter erosion and failure in traditional filter sub designs. The chamber capacity for debris is larger than other filter subs to extend the operating envelope before the chamber is full. The double-screen design provides a highly robust solution, with the debris contained in a large total flow area.
The tool has run for more than 1,700 hours on the same screen with no erosion, a marked improvement over conventional single-filter designs, where the single screen can erode quickly as a result of high fluid velocity, often failing in 100-150 hours. The internal filter is resistant to erosion and causes minimal pressure loss in the circulating system. A contingency 400-psi central bypass allows wireline access without requiring prior recovery of top-sub components. When the drilling cycle is complete, the filter is pulled out with the drill string, allowing the operator to empty and examine the captured material at surface prior to rerunning the tool.
Flow dynamic software was used to determine an optimal design, while the 3/16-inch filter slots vary in length to harmonize the flow path along the entire screen length, which is approximately 50 inches. In applications to date, it has not been necessary to pull the tool early because of a full chamber. In the event the chamber does fill up, flow is diverted internally past the screens, coming out in the central bore and down through the drill pipe.
The filter has been deployed for 36 directional drilling operations in the U.S. land market, as well as in global markets, including the Middle East, Argentina and Canada. The tool has thus far logged more than 12,000 pumping hours and drilled more than 550,000 feet with no failures.
In field trials in Argentina, the same 4 ¾-inch work string filter was run consecutively in seven extended-reach wells in an offshore shale formation, capturing more than 10 pounds of fluid-borne circulation debris with no replacement screens. Deploying the tool extended the run life of the BHA components, including RSS equipment, eliminating NPT. The operator ran the filter for 1,950 total hours and drilled more than 56,893 feet without having to pull out of the hole for a premature BHA failure.
