№ 10 (October 2006)
New Schlumberger Technologies Heighten Frac Treatment Efficiency
Three new technologies from Schlumberger are substantially improving the effectiveness, environmental friendliness and treatment time performance in hydraulic fracturing worldwide.
By Salvador Ayala
They are playing an especially important role in Russia, where a high percentage of wells need fracturing and climate and logistical difficulties pose stiff technical and economic challenges.
The technologies are all part of the Surface Efficiency Program the company has initiated for fracturing services. These three innovations include:
• Fiber technology to enhance proppant distribution.
• A reduced-guar, crosslinked fracturing fluid system that is water based and hydrocarbon free.
• A continuous mixing and hydration unit for “dry on the fly” mixing of polymer fluid.
The challenges prominent in the Russian market have been major drivers of these innovations. The technologies themselves were developed in Russia, or their development received strong guidance from Schlumberger Russian product development centers, field services experts and Russian customers.
Fiber System Enables Reservoir-Tailored Proppant Transport and Placement
When fluid viscosity falls below the critical threshold required to suspend proppant during hydraulic fracturing operations, a significant adverse impact on productivity can result as proppant settles and reduces fracture geometry and hence production.
The FiberFRAC* fracturing fluid technology decouples proppant transport from fluid viscosity. This newly developed system creates a fiber-based network within the fracturing fluid, providing a mechanical means to transport, suspend and place the proppant. Because proppant transport no longer relies on fracturing fluid viscosities, it can be tailored to reservoir conditions to optimize fracture geometry.
If needed, fracture height growth can be controlled through use of a low-viscosity fluid – even at high temperatures – while maintaining the necessary proppant transport. Furthermore, in crosslinked polymer treatments, the retained proppant pack permeability can be significantly increased because less polymer loading is required. Laboratory testing has shown that decreasing polymer loading by 40 percent can increase retained permeability by 24 percent. Additionally, laboratory tests and field applications have demonstrated that the fibers do not adversely affect retained proppant pack permeability or fracture conductivity.
Extensive field applications of this technology have shown significant production increases, in some cases up to 60 percent, compared with production performance following conventional treatments in offset wells.
In a recent case study, a major North American producer compared the performance of a well fractured using this new fiber technology with the performance of an offset well conventionally fractured. The treatments were performed within four days of each other and the wells continuously monitored for optimal direct comparison.
Treatment of the conventionally fractured well consisted of around 250,000 lb of proppant pumped at 35 b/min. Polymer fluid was injected at 30 lb/1,000 gal with no fiber added. Post-treatment well production was 0.3 mmcf/d of gas and 360 b/d of water at 750 psi wellhead flowing pressure. A considerable pressure drop at the final treatment stage suggested excess fracture height growth in high-water-saturation zones.
Treatment of the well receiving the fiber technology application consisted of 205,000 lb of proppant pumped at 35 b/min. Post-treatment well production was 2.2 mmcf/d of gas and 30 b/d of water at 5,000 psi wellhead flowing pressure. This represented more than a sevenfold increase in gas production and much lower water production compared with the offset well. No pressure drop was observed during treatment, leading the operator and Schlumberger to infer that the fiber application helped maintain the stimulation treatment within the zone of interest.
Environmentally Friendly Crosslinker Technology Meets Special Siberian NeedsThe CleanGEL YF 100-RGD* crosslinked, water-based fracturing fluid system was first used in Siberia. This fluid can be easily customized for specific projects and is specially formulated for extremely cold working environments.
Because it is hydrocarbon free, the fluid eliminates environmental and cold-weather handling concerns associated with diesel-fuel slurries. It also employs an environmentally friendly surfactant. Delayed crosslinking allows easier fluid placement. The fluid hydrates quickly and maximizes the use of dry additives. The reduced polymer, guar and additive requirements of the fluid result in cleaner, more conductive fractures; easier handling and faster cleanup. Pre-job preparation, including batch mixing and the blending of chemicals and crosslinker solutions, is also minimized. Combined, all of these efficiencies lead to shorter treatments and lower costs.
Not long ago, the screen-out rate for frac treatments in Western Siberia was running at 25 percent. With the introduction of this fluid system, that rate has fallen to 10 percent and resulted in fewer coiled-tubing cleanouts, major cost savings and earlier production.
Russian-Designed Unit Continuously Mixes Polymer on Site and on DemandThe GelSTREAK* gel continuous mixing and hydration unit is designed to reduce the equipment footprint of fracturing jobs as well as enable the use of environmentally friendly fluid systems. The large amounts and varieties of materials used in fracturing require a unit capable of mixing fluid continuously and on-demand. This remotely controllable unit is capable of adding dry polymer on the fly with highly precise hydration while adjusting the guar concentration as required by job design. The unit can handle the latest generation of dry guar-based systems, and all field storage of chemicals is eliminated. Use of this unit typically cuts treatment time by a whole day through eliminating the sequence of prior mixing and moving the mixture to tanks then pumps. The inevitable waste of batch mixing is also avoided. This unit was designed and is now exclusively built in Russia, incorporating a specially modified 6-by-6, all-wheel-drive Russian chassis for efficient, reliable mobility under even extreme road conditions.
Meeting these mobility requirements is likewise essential for the on-site monitoring and control units deployed in blending and directing the overall fracturing treatment. The PodSTREAK* unit is a smaller, highly mobile version of the Schlumberger POD* programmable optimum density blender. With its reduced size and footprint, this smaller unit is specially scaled for the economic and technical needs of frac jobs prevalent in mature provinces such as Western Siberia; West Texas, USA; and Alberta, Canada. Recently, a special 6-by-6 version of this blending unit has been developed for the Russian market. In all, the efficiencies achieved in Western Siberia resulting from the crosslinker and treatment delivery innovations described herein have led to a 250 percent increase in the job completion rate over a recent eight-month period and a substantial reduction in the winter treatment backlog. In addition, there has been a 10 percent reduction in product cost and an average time savings of 10 hours per treatment stage. These achievements together translate into added value for the customer.
* Mark of Schlumberger