Oil and gas producers have succeeded in boosting production from horizontal wells in unconventional reservoirs over the last decade. This is attributed to advances in directional drilling, longer laterals, and multi-stage stimulation techniques. Additionally, changes in completion strategy, such as tightening stage spacing, also has been beneficial. An engineering study in the Haynesville and Bossier shales shows a 22% production increase (4.5 to 5.5 Bcfg) per well, as average stage spacing between perforations dropped from 272 ft to 150 ft between 2011 and 2013. Completion designs also have trended toward higher fluid and proppant volumes.
DEVELOPING COMPLETION SOLUTIONS
Similar to how horizontal drilling and hydraulic fracturing were combined to access previously uneconomical unconventional reservoirs, combining the efficiency of ball-drop technology with the accuracy of fracture placement, in cemented liner completions, provides producers with a method that reduces completion time/costs, improves operational efficiency and increases production.
Limited-entry ball-drop evolution
Packers Plus introduced its first limited-entry ball-drop system in 2004. The initial tool design included a cutter assembly and multiple shear-activated stimulation jets. The actuation ball would land in the cutter assembly and then travel along the treatment zone, opening each jet along the way. The system could be configured with multiple jets in-between each packer, or with one jet between each packer, creating multiple, individual entry points. The nozzles were designed to be adjusted and placed according to reservoir characteristics, thus enabling controlled injection of completion fluid along the entire length of each stage. The tool allowed operators to strategically place acid treatments for maximum benefit. The completion system was commissioned in several prolific carbonate formations.
As limited-entry ball-drop technology advanced, the cutter assembly was removed from the system, and the jet nozzles were activated directly, using an actuation ball pumped from the surface. Used for delivering both acid and proppant stimulation treatments, the versatility of limited-entry ball-drop completion technology was established.
QuickFRAC cemented liner completion system
The company recently launched a pilot program in the southern U.S. to design and test a new multi-stage completion system called QuickFRAC (QF). The QF system aims to expand on the efficiencies created by ball-drop technology, when combined with the accuracy of limited-entry fracture placement in cemented liner completions. The main focus of the new technology is to stimulate a high number of entry points in one treatment, remove the risk of wireline and coiled tubing runs, and eliminate the need to mill out tools/plugs prior to flow-back.
QF utilizes multiple sleeves during treatment and is triggered by using a single actuation ball. The entry point of each sleeve is reinforced to prevent erosion, and can be designed so that each sleeve has its own back-pressure. QF can be used to selectively stimulate the reservoir independently at each sleeve, providing multiple entry points in a stage. Using proprietary squeeze technology, the sleeves are designed to accommodate a high number of entry points in each stage. Additional efficiencies are realized by pairing the QF system with degradable ball technology. This enables operators to further reduce operational risk and eliminate mill-out requirements.
QuickPORT IV sleeve
A new QuickPORT IV sleeve (QP) is a simplified mechanical assembly with approximately 40% fewer components than earlier sleeve designs. The new QP sleeves are reinforced with tungsten carbide flow ports to prevent issues associated with perforation erosion, which helps facilitate fluid distribution to multiple entry points. Pumping rates can be achieved to place fractures in the proper predetermined positions to achieve optimal fracture length. In this design, stages are not over-displaced, increasing near-wellbore conductivity.
Premium liner hanger packer
The liner hanger packer uses premium sealing technology to pack-off the annulus and secure the completion liner in intermediate casing. The new-style hanging system uses a seal and hold-down slips that can withstand differential pressures up to 10,000 psi. The tool’s capabilities include:
?A balanced piston prevents pre-setting during run-in
?The ability to rotate, push/pull without early release of the setting tool
?A bonded element design allows for higher circulation rates and liner run-in speeds without damaging the element
?It provides reaming capabilities by handling a high level of torque
?Built-in redundancies of a float nut and secondary release option ensure reliable operations.
Testable toe sleeve
The hydraulically activated initiation sleeve enables multiple pressure tests up to maximum casing pressure before opening the sleeve for stimulation. Capabilities include:
?Pressure testing independent of stimulation operations, without time constraints
?Full compliance with North American casing integrity test requirements
?A redundancy feature that ensures full sleeve opening
?Adjustable activation and opening shear
?Ports that provide a flow area greater than the liner.
Application engineering function
To ensure a system solution that is optimized for a specific job, an engineering team calculates pump rates, friction factors and pressure drop, in addition to torque and drag for each completion. The comprehensive analysis, combined with the team’s technical expertise, ensures a successful QF installation and effective reservoir stimulation.
CASE STUDIES
The first QuickFRAC cemented completion system was installed as the first stage at the toe end in a 12,000-ft, MD, Mississippian well in Oklahoma. It also included five QuickPORT sleeves spaced approximately 45 ft apart, in addition to a hydraulically activated toe sleeve. The toe stage was activated for a diagnostic fracture injection test, two weeks before the rest of the wellbore was stimulated. Once pumping procedures were initiated, the five sleeves were opened with one degradable actuation ball followed by a slickwater treatment pumped at 100 bbl/min. The entire completion operation for the stage was finished in approximately 2 hr less than a typical completion using a PnP method. In addition to eliminating the need to run a perforating gun, the degradable ball technology reduced mill-out time prior to flow-back.
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