This engineered composite ball was recovered from a well in Canada. The lines engraved in the ball show that it seated firmly and remained intact.
Swellable packers, however, are just one piece of modular multizone completion design. While the industry as a whole has been slow to adopt modular completion technology, there is real money- and time-savings to be gained, given the increasing complexity of the reservoirs.
Customized approach
It is surprising how many operators still use the old “plug and shoot” approach to multizone wells: cement the liner, run in the gun to perforate the lowest zone, pull out, frac, run in to set a composite bridge plug above that zone, shoot a new zone, and so on.
A more effective approach is to eliminate most trips while ensuring that each zone is optimally isolated and fractured. The design of each zone’s completion should depend on the formation characteristics, hole condition, and whether or not the operator plans to open and close the zone in the future. The ZoneSelect system is designed to allow each zone completion to be customized independently on a single string of tubing.
Selecting the ideal configuration enables optimal diversion of the fracture stimulation ? without the expense of thru-tubing intervention ? and provides life-of-well zonal-isolation potential. Since its launch in late 2008, the system has been used to isolate more than 750 zones in the US and Canada.
To give engineers maximum design flexibility, the system includes four isolation methods and three frac distribution sleeves, all with mix-and-match interconnectivity.
Options for isolation include the Fraxsis swellable packer plus traditional hydraulically set packers, high-pressure inflatable packers, and cementation.
The most common sleeve option for controlling access to the frac zone is the single-shot: Sleeves are opened from the bottom up by successively larger balls: After a ball opens a particular sleeve, it lands above the previous sleeve and seals off the previous zone. After being opened, each sleeve remains open permanently. At the end of the frac job, the balls are produced out of the hole and the ball seats are milled out of the tubing. This inexpensive approach can be used for up to 16 zones (with the capability to do as many 22) where future zonal isolation is not anticipated.
The second approach a multishift sleeve, also good for up to 22 zones. The multishift sleeve works in the same ball-drop manner as the single-shot, but it also features a secondary open/close capability: A shifting tool run in on tubing can be used later to close or reopen sleeves to optimize production. A patented shock absorber built into the multishift system maintains the integrity of the sleeve as both a frac diverter and zonal-isolation device. Because the opened sleeve may later need to be shifted closed, damage from the ball hitting and knocking down the sleeve is a concern; the shock absorber helps eliminate this concern.
The third, less common, approach is the monobore frac sleeve. It is typically used when the isolation zone must be cemented to compensate for unconsolidated formations or for high temperatures that would degrade a packer. Cement precludes the use of ball-drop sleeves (single-shot or multishift) because the dart that cleans cement from the inside of the bore would trip the sleeves. The advantage of monobore is that there are no ball seats to mill out, and because there are no ball seats, zones can be treated in any sequence. The disadvantage is that running the shifting tool in and out for each zone takes rig time.
Customized multizone frac systems can substantially reduce the rig time normally required to isolate and stimulate multiple zones. For instance, in the heel of a horizontal well, the operator may choose to install a swellable packer to deal with a washed out well bore, plus a multishift frac system to shut off water production in the future. Closer to the toe where zonal isolation isn’t likely to be an issue, they may prefer a hydraulic packer and single-shot sleeve system.
Maintaining pressure
The Fraxsis annulus swellable packer incorporates patented metal reinforcement that enables it to hold up to 6,000 psi in lengths of only 7 ft (2.1 m).
One innovation that markedly enhances the effectiveness of the system is a new engineered composite ball, exclusive to Weatherford. These balls can hit the ball seat at very high flow rates without shattering, then seat firmly, hold 10,000 psi, and flow back out of the well without sticking. Standard balls often shatter on impact, and the only thing field personnel can do is drop another ball.
An option on all sleeves is the patented outer composite sleeve, which prevents damage to the seal surfaces of the sleeve from formation debris during run-in or from cement contamination. When the frac sleeve is shifted open, the pressure pulse from the fracture disintegrates the protective sleeve, made of the same materials as the composite bridge plugs.
Marcellus case history
A major operator in northeast Pennsylvania was planning to fracture nine zones in a Marcellus shale well 10,235 ft (3,121 m) deep. In the past they had employed the “plug and shoot” method but were now seeking a more streamlined approach to multizone stimulation. The first attempts involved conventional 10-ft (3-m) inflatable packers, but the operator had trouble getting these long packers down the hole.
For this well, they chose the 7-ft Fraxsis swellable packer and the ZoneSelect single-shot fracturing sleeve for all nine zones. They had no problems running in the string. And with every ball-drop, they could follow the pressure rise to see exactly when the ball hit, when the sleeve sheared open, and when the frac started. This was made possible by the resilience of the engineered composite ball ? and they had not been able to see this previously with conventional balls, where many zones required more than one ball-drop.
Each zone was fractured without any issues, and at the end, the cast-iron ball seats were milled out in an average of only 5 min/seat. Overall, the operator estimates that this modular system saved them two full days of rig time ? not including the time they had previously spent dealing with hang-ups caused by the 10-ft inflatable packers.
楊寶劍 是全球石油網的高級技術編輯，在石油技術資訊行業有八年的學識和經驗。他源源不斷地提供石油行業全球最新的技術創新、研發成果、現場應用情況等信息。如果你對“新技術新產品”的內容有任何問題或建議，請聯系楊寶劍編輯 +86 10-58236512 Email：allenyo@zhenweiexpo.com 歡迎您提供手中的最新技術文章！
發布信息
