While neither of the examples below are tight gas, these technologies are often used in tight-gas wells. Operators often encounter problems when attempting to isolate and fracture multiple pay zones using conventional openhole completion and stimulation methods. In many cases, conventional completion methods cannot be used because they allow only partial treatment of a zone. Using these methods, operators typically can perform only three or four fracture stages per well, per day.
A RapidStageTM pinpoint stimulation/completion system employs sliding-sleeve technology, a swellable isolation system, and an expandable liner hanger (ELH) system to accurately place several individual stimulation treatments, without additional intervention. Using this completion system helps reduce the total time and cost required to complete multiple intervals. This technique has been used to treat more than 850 stages/zones in 120 well completions, with up to nine zone completions in a single day. A series of progressively larger balls is dropped into the well throughout the multistage pumping operation to selectively access different pay zones, up to 10, in a single installation. As each of the balls falls on tapered baffles in the sleeves, the sleeves open in sequence, sealing off the previously treated zones below, thereby allowing the pumping of treatments into the zone. The ball-drop procedure allows a totally interventionless completion. Once opened, a shifting tool is used to close and reopen the stimulation sleeves to allow restimulation or workover, at a later date.
Bakken Shale, North Dakota
The Bakken shale is a low-permeability shale play in North Dakota and Montana. Conventional completions consist of treating a typical 6,000-ft to 12,000-ft lateral borehole as one large fracture stimulation stage. The RapidStage horizontal interventionless completion system was installed in two wells in a Bakken field. Well 1 was divided into four stages using SwellPacker® isolation systems to isolate drop-ball-actuated sliding sleeves to allow interventionless stimulation and VersaFlex® ELH system to tie into the parent casing. Well 2 was divided into six stages using the same procedure. Both wells were fracture stimulated by dropping balls to activate the sliding sleeves. The efficiency of the drop-ball method allowed stimulation of all the stages in a single day, resulting in lower well-completion costs. The interventionless completions also increased production in these wells, compared to conventionally completed offset wells: the highest three-month production from Well 1 was 158% of the average production for three offset wells, and the highest three-month production for Well 2 was 175% of the average production rate of the three offset wells.
James Lime, East Texas
A conventional completion in the James Lime, a naturally fractured carbonate reservoir in east Texas and north Louisiana, consists of a drilling a 2,000-ft lateral underbalanced, and stimulating the entire lateral in a single treatment, first with a large acid treatment, followed by a large sand treatment. An IOC operator needed to stimulate five naturally fractured intervals in a horizontal wellbore with multiple pay zones. Normal cementing completion methods would restrict production and were not an option. The operator chose the RapidStage system to provide isolation between the formation and the upper wellbore and a means to tieback to the surface. The completion process included the Swellpacker® system to isolate the annular area between zones.The well was fracture stimulated by means of acid and sand fracs pumped into each stage. The job was pumped continuously by pumping different sized balls to open the sliding sleeves and divert the treatment into each new zone. A wellhead problem forced a shutdown between stages four and five. A positive pressure response was recorded when breaking down each zone, indicating that the Swellpacker systems were isolating each stage, as intended. Using this service, the five zones were successfully stimulated in 20 hr, using 1.3 million lbm of proppant and 2.1 million gal of gel. This completion method lowered the overall completion costs and improved the completion-cycle time while allowing the natural fractures, a major source of production, to remain open, rather than closed off by cement (conventional completion). The RapidStage system provided an economical completion of multizone wellbores that involved minimal, or no intervention.
SPE 115476 "Completion System Allows for Interventionless Stimulation Treatments in Horizontal Wells with Multiple Shale Pay Zones"
Greg Vargus, Matt Howell, Ron Hinkie, James Williford, and Tim Bozeman, SPE, Halliburton