The Upper Devonian play within Pennsylvania has been the predominant focus of most operators for many years. These sandstone and siltstone formations are regularly hydraulically fractured with a variety of fluids ranging from high concentration crosslinks, linear gels, polyacrylamide slick waters and even treated fresh water. These fluids, although economical, lack quality and can cause severe damage during the stimulation process. Whether it is leaving behind heavy residual damage or not supplying enough viscosity to carry proppant deep into the created fracture, these fluids do not offer the advantages of an all-inclusive system.
Recently, with the development of visco-elastic surfactants (VES's), a standalone, total package fluid is available at an economical cost. VES's offer high quality with no polymers, giving us a completely clean fluid without residual damage. They can be designed to supply a wide range of viscosities with excellent carrying properties to help ensure optimal proppant placement. With the fluid being surfactant based it is a good foaming agent, which provides exceptional water recovery and strong flowbacks.
Best of all, these fluids are all-inclusive, removing the need for additional additives. It consists of one on-the-fly additive that is compatible with extremely poor quality water that may have been reused. There is no need for additional clay controls, biocides, surfactants or iron controls, but in extreme cases, their additions do not create any compatibility issues. This allows VES's to deliver a high quality system at a competitive price.
This paper will take an in depth look at visco-elastic surfactants and their current applications in the Upper Devonian throughout Pennsylvania. It will highlight the treatment design, operational execution and production results from a variety of wells during the initial application of VES fluids.
For many years, the stimulation of Upper Devonian gas plays in Pennsylvania has been approached from the same standpoint, quick and dirty. Most operators have searched for the most efficient, cost effective way to stimulate multiple stages and put the well inline as soon as possible. From ball and baffle zonal isolation, reused waters, forced closure flowback, low cost fluid systems and marginal economic return, the Appalachian Basin has had few options for improved stimulation fluid applications. Because of this, there has been concern about the quality of treatments and elicited ongoing research by the service industry to improve current practices.
One major focus area has been fracturing fluids and developing cleaner fluid systems with reduced damage to formations of interest. Currently used guar gel and friction reducer systems can cause unwanted residual damage to the formation face and proppant pack, plugging off possible permeable pore throats. Even with the use of advanced breaker systems, large amounts of residuals can be left behind. Other major quality issues that must be considered include reused waters, large amounts of bacteria, sediments, and fines, which can be pumped into formation causing irreversible damage. All of these factors help support the need for a clean, versatile fluid system and initiated the use of visco-elastic surfactants (VES's) in Appalachian Basin.
Since the beginning of 2007, over 100 wells have been completed using VES's with great success in Pennsylvania. These wells have been located in a wide range of counties including Jefferson, Center, Clarion, Clearfield, Armstrong, Butler, Indiana and Westmoreland. Predominantly, the lower pressure sand/siltsone formations, found throughout the Upper Devonian, as in Table 1, have proven to be excellent candidates for the VES treatments. Their mineralogy, which contains large quantities of quartz and some clay, exampled in Table 2, has responded very well to this innovative treatment. As well as offering a cleaner fluid system, VES's have facilitated in greater fluid recovery, clay control, and bacteria control relative to the systems surfactant properties. With there being various visco-elastic surfactant systems available today, this paper will take a look into the system and its applications from a generalized standpoint in Pennsylvania.