A former fracture engineer for five years, Jeffers once saw almost all completions started in this basin as strictly PNP operations. This completion methodology was not bulletproof, though. “We just weren’t getting it done,” he said. “On a 10-stage well, we would spend a week to two weeks on a well. We went from PNP to openhole completions and compared the results to see if they were better or worse. We got better results.”
Completions have gotten more difficult over the last half-decade, and lateral lengths have grown significantly longer, with stage counts increasing and well cycles significantly decreasing, said Mark Morris, Baker Hughes operations manager, northeast US, summarizing significant changes he has seen take place.
Operators and service companies are applying a panoply of advanced tools and technologies in the Appalachian basin. Companies showcasing technologies and tools include Magnum Hunter Resources, which operates an 18-well pad (Stalder pad) that will serve as the base for a robotic rig (Schramm T500XD); an openhole 20-stage fracturing system from Packers Plus Energy Services (StackFRAC HD), plus a StackFRAC case study; two software applications from Halliburton (ShaleXpert and TightGasXpert), plus wireline and perforating tools (monoconductor tension device [MCTD]); advanced drilling fluids from Newpark (synthetic-based CyberPhase and diesel or mineral oil-based OptiPhase); lateral drilling advances from Schlumberger subsidiary PathFinder (PowerDrive Archer high-build rotary steerable system [RSS]), including a Marcellus shale case study; and the introduction of advanced drillbits from Baker Hughes (Talon 3-D Vector-Accurate polycrystalline diamond compact [PDC] bits), its invert emulsion system (NEXT-DRILL), and its AutoTrak Curve RSS.
Shifting from cemented completions to openhole techniques
Not only are changes prevalent for drilling technologies and fluids technologies, completion methodologies show anything but the status quo. It is apparent more openhole completions are now evident in the Appalachian basin, said Jeffers from Packers Plus.
He added that for under-pressured shale plays he is seeing much in the way of nitrogen fracturing. “Just 100% nitrogen – no chemicals, no sand. We’re pumping 1 MMcf per stage at 100,000 cf per minute,” Jeffers said.
Multistage fracturing system a success
The Packers Plus StackFRAC HD multistage fracturing system has increased reservoir access in Kentucky.
Estimates of natural gas are high in the Devonian shale, but this has been tempered by low recovery rates averaging 10%.
An operator working in the Devonian shale wanted to prove out a multistage completion technology as he prepared for drilling and completing longer laterals in the area. Extending the reach of openhole laterals was necessary to meet the operator’s objectives of optimizing production and lowering costs.
It became necessary to find a multistage completions system capable of handling additional stages to cover the length of the extended-reach laterals.
The operator used a Packers Plus StackFRAC HD multistage fracturing system, as it allowed for more stages in a single system. As a result, it is now running the system exclusively vs. the standard system. The well design was for a TD of 6,325 ft and a lateral length of 3,435 ft, and the average length between the stages was approximately 200 ft.
All 18 stages were fractured and completed in one day. These were gas fractures using 500 Mcf of nitrogen per stage.
Ongoing completions discovery
According to Baker Hughes, traditional completion methods consisting of cemented long strings and composite plugs also are being deployed in the Appalachian basin. This is primarily driven by pad size and water management challenges.
Over the past several years, operators and service companies have worked to optimize the PNP completion method with a combination of composite fracture plugs, coiled tubing (CT) and wireline perforating systems, and CT conveyed milling services. During this completion process, the liner is run to TD in the horizontal well and cemented in place. To gain access to the formation to begin fracturing, the first stage has typically been perforated using tubing-conveyed perforating guns and then fractured. To complete the next stage, a composite fracture plug and perforating gun assembly is run to the desired depth; the plug is set to isolate the zone; the guns are fired to connect the well to the formation; the guns are retrieved; a ball is dropped; and the stage is fractured. This process is repeated 20 or more times until the entire lateral is fractured. Then a CT milling assembly, including a downhole motor and specialized mills, is run in the well to remove the composite plugs and fracture balls, removing flow obstructions and enabling full production.
CCPP or openhole?
In the Marcellus shale, Packers Plus has reported using openhole systems to maximize assets where challenges like low porosity and permeability have demanded cost-intensive completion solutions.
“When compared to openhole completions, some will contend that cemented casing plug-and-perf (CCPP) methodology is more cost-intensive due to the additional time and equipment. This results in an inefficient and time-consuming process. Production using this method also can be limited, as cementing a wellbore can reduce or eliminate communication with natural fractures and fissures that might contribute to overall production.
Packers Plus has developed openhole, multistage systems so operators can take advantage of natural fractures and obtain maximum contact with the formation. These openhole completions allow for production from the entire length of the wellbore, as opposed to CCPP, which restricts production to perforations only, according to Packers Plus product information.
Openhole systems maximize assets in the Marcellus shale
A comparison study was done in the Marcellus to measure production of 17 wells completed with Packers Plus StackFRAC HD systems compared to surrounding offset wells in the field completed using the CCPP method (SPE paper 155095). The two study areas were in Washington County, Pa., and Susquehanna County, Pa., and cumulative production was compared at six, 12, and 24 months.
In both study areas, the wells completed with StackFRAC HD systems outperformed the CCPP completed wells producing from 43% to 84% higher in Washington County and up to 37% in Susquehanna County compared to the offset CCPP average. In addition to higher production, the StackFRAC HD systems also provided improved efficiency and cost savings compared to the CCPP method. The system’s completed wells were stimulated in less than a day compared to approximately two to three days required for the CCPP wells. This efficiency also reduced equipment and personnel costs.
Schlumberger’s Wutherich brings a different perspective to the table. “By far, the vast majority of shale wells being targeted in Appalachia are being completed with horizontal wells that are cased and cemented,” he said, adding hydraulic fracturing on such well completions uses the PNP-ft technique in which several stages of three to seven clusters of perforations spaced 40 ft to 100 ft apart are fractured simultaneously. “Most often operators are using slickwater type fracturing treatments or a hybrid-style treatment with slick water followed by a more viscous linear or crosslinked gel depending on the specific reservoir properties,” Wutherich said.
Wutherich added that due to the relaxed nature of the Appalachian basin, the magnitudes if the principal horizontal stresses are very close to one another. This can lead to the creation of a complex fracture network when hydraulic stresses are applied, as opposed to more bi-wing type hydraulic fractures that may be found in more tectonically active basins. “It is believed that this complexity is further enhanced by using very close cluster spacing, which is why a cased-hole completion is used.”
One emerging trend, referred to as the super-frac technique, uses reduced cluster spacing. Fracture stage lengths are decreased, while the spacing between perforation clusters also is decreased.
“By effectively increasing the number of fracturing stages performed on the well, operators can ensure that the entire lateral is better stimulated,” Wutherich said. “But this results in significantly higher costs and time required to complete the well.”