Viscoelastic surfactants (VES) are important gelling agents in well stimulation treatments. Proper job design requires that the additives create the desired viscosity for effective proppant or gravel pack sand transport. Post-stimulation production enhancement partially relies on the thoroughness of gelling agent destruction or removal, known as "breaking" the gel. VES gels are non-damaging and do not create a filter cake, and thus are prone to high leak-off. The leak-off fluid potentially has a high zero-shear viscosity and can be challenging to remove from the formation. We propose a breaker system that comprises a monomer and radical initiator that will travel into to the formation with the VES gel. The resulting polymer will disrupt the worm-like micelles of the VES, creating spherical micelles and reducing the viscosity of the fluid. The breaker system presented here is operable at 200 °F. Rheology measurements show that the VES fluid with monomer and initiator has reduced viscosity and becomes less shear-thinning. Optical transmission and backscattering measurements show that the presence of breaker does not greatly accelerate proppant settling. The reduced viscosity would not adversely affect proppant transport. Core flow experiments compared retained permeability of cores treated with VES and VES with reacted monomer and initiator. The core flushed with broken fluid possessed a retained permeability of 79%, while the unmodified VES left only 44% retained permeability.
Ejofodomi, Efejera (Schlumberger) | Sethi, Richa (Schlumberger) | Aktas, Elcin (Schlumberger) | Padgett, Julie (Schlumberger) | Mackay, Bruce (Schlumberger) | Mirakyan, Andrey (Schlumberger) | McCrackin, Ben (Manti Tarka Permian) | Douglas, Chris (Manti Tarka Permian)
This paper was prepared for presentation at the Unconventional Resources Technology Conference held in Houston, Texas, USA, 23-25 July 2018. The URTeC Technical Program Committee accepted this presentation on the basis of information contained in an abstract submitted by the author(s). The contents of this paper have not been reviewed by URTeC and URTeC does not warrant the accuracy, reliability, or timeliness of any information herein. All information is the responsibility of, and, is subject to corrections by the author(s). Any person or entity that relies on any information obtained from this paper does so at their own risk. The information herein does not necessarily reflect any position of URTeC. Any reproduction, distribution, or storage of any part of this paper by anyone other than the author without the written consent of URTeC is prohibited.
The modern horizontal multistage well is a main contributor to the recent transformation of North American oil and gas production. The large fracturing stage volume that defines unconventional wells, crossed against the increasing numbers of stages and laterals per pad, has dramatically increased the demand for fracturing materials such as sand, friction reducers, and gelling agents, and most especially water. At the same time, operators face increasing accumulations of produced water, which presents as water cut from more mature assets. It is therefore natural to propose using produced water as mixwater for fracturing fluids in new completions, but in practice this plan has met with two major barriers: first, regulatory and logistical hurdles concerning the storage, handling, and potential environmental impacts of the volume of produced water required to complete a modern well (millions of gallons per lateral), and second, technology gaps in the applied chemistry of completion fluids, particularly in crosslinked gels.
This paper reports the completion of a two-lateral well in the Williston Basin where produced water, filtered but otherwise untreated, was used throughout the slickwater and crosslinked components of about sixty hydraulic fracturing stages.
Proppant was successfully placed in all perforated zones in the Bakken and Three Forks formations, using a “hybrid” design that employed seven million gallons of water (of which 2.2 million gallons were crosslinked). Production figures for the well are satisfactory, and this is discussed in the context of fluid-related completion quality. This paper will concentrate on the development and implementation of a metal crosslinked fracturing fluid that shows excellent stability at typical Bakken conditions. We will present a comparison to conventional guar-borate systems.
The promise of this approach has many potential benefits. First, completion costs are decreased as freshwater sourcing and produced water disposal charges cancel each other. Second, far fewer truck trips are necessary to transport water. Third, the industry no longer requires fresh water sources or disposal wells where this technique is employed.
Zhang, Bin (Verenium Corporation) | Davenport, Adrienne H. (Verenium Corporation) | Whipple, Lawrence (Verenium Corporation) | Urbina, Hugo (Verenium Corporation) | Barrett, Kenneth (Verenium Corporation) | Wall, Mark (Verenium Corporation) | Hutchins, Richard (Schlumberger Technology Corporation) | Mirakyan, Andrey (Schlumberger Technology Corporation)
Enzyme breakers have been previously used for hydrolyzing guar gels at temperatures below 150°F. There is an industry-wide demand for enzyme breakers that can function under higher-temperature (200-250°F) and extreme pH (=10.5) conditions. To meet this demand, efforts have been made to develop an exceptionally thermostable cellulase enzyme, referred to hereafter as mannanase, that was originally discovered in a hydrothermal vent sample. This mannanase exhibits well-differentiated performance under extreme downhole conditions encountered in gas shales and deeper oil/gas wells.
This superior mannanase can effectively break linear and borate crosslinked guar under broad ranges of temperature (80°F up to at least 225°F as seen by rheology, and up to 275°F using residual activity analysis) and pH (3.0 up to 10.5). The results of rheological tests show that only a small dose is required (100 ppm or less) to achieve the complete break. The enzymatic reaction can be triggered by the changes of temperature and pH during fracturing operations. This mannanase also exhibits a dose response that allows the operator to generate a desirable viscosity/time profile by adjusting enzyme dosage. Even in the presence of fluid additives, such as buffers, salts, stabilizers, and crosslinkers, this mannanase is active for effective viscosity reduction.
This mannanase breaker belongs to the glucanase family. It reduces gel viscosity by specifically targeting ß-1,4 glycosidic bonds between the mannose units in guar. The carbohydrate-profiling tests demonstrate that this enzyme effectively and efficiently breaks the long-guar polymers into small, soluble fragments that will eliminate gel rehealing. The conductivity tests demonstrate extensive cleaving of guar and removal of polymer residues that cause formation damage and reduce fracture conductivity.