No abstract

This paper was prepared for presentation at the 1999 SPE International Symposium on Oilfield Chemistry held in Houston, Texas, 16-19 February 1999.

This paper presents a new zeta potential altering system that is based on an inner salt developed to enhance the water flowback recovery on borate and slick-water frac jobs. The system also aids in the control of fines. The mechanism of this system is to modify the zeta potential on particles such as frac sand from -50 mV, or coal from -28 mV, to more neutral values. This modification helps increase the potential for particle agglomeration and changes in the sand pack in the fracture to increase fluid recovery and production.Results from lab studies have shown that the flow rate ratio for a 2% KCl solution through sand packs (treated/not treated) increased up to 45% when treated with 6.0 gal of chemical per 1,000 lb of frac sand. Similar results were obtained on conductivity tests using ceramic proppant, improving conductivity from 7,150 mD-ft to 11,387 mD-ft at 2,000 psi closure stress.This new system does not interfere with fracturing fluid rheological profiles for borate systems and improves friction reducing characteristics in slick-water systems.The system was tested in the field on a slick-water job, where the additive was mixed in the blender tub.

Flowback aids have been long reported in the literature as being beneficial to enhance clean-up after stimulation treatments, and in particular hydraulic fracturing. The goal is for the flowback aids to allow the piston like flowback and return of fluids from the reservoir resulting in minimal losses to the formation and no memory effect that hampers back production. Microemulsions have also been reported in the literature and a review (including patent landscape) creates somewhat of a myth around their exact mechanism of performance and benefit to the application.The present work was concerned with the development of flowback aids based on micro-/nanoemulsion technology for enhanced gas and oil recovery after fracturing application. The goal was to formulate microemulsion concentrates which form nanoemulsions when diluted into fracturing fluids and provide strong surface and interfacial tension reduction to minimize reservoir damage.Microemulsions have been formulated with various possible surfactants and oil systems. The performance of the different formulations has been evaluated with different test methods, adopted from literature and industry best practice in order to screen for most promising microemulsion systems and compared to their aqueous equivalents to determine the performance benefits offered by emulsified packages. High throughput experimentation and robotic formulation was utilized to screen several thousand formulations from nearly 50 different surfactant packages. This allowed for incredible synergistic properties to be discovered very quickly and efficiently. The development of a new class of microemulsion package that is made up of almost 100% renewable and environmentally friendly components has made a large step change towards the state of the art of this class of flowback aids.Regain permeability and core flow testing was performed on the best performing microemulsion formulations to determine the effect of field application. The result of this work was that microemulsions do offer some benefits over individual surfactants, not so much in surface tension modification but very much on the non-emulsification of crude oil and water and multiphase flow in porous media -so often seen as the primary damage mechanism in oil well fracturing.

Guar gum and its derivatives are the most frequently used thickening agents in hydraulic fracturing. They account for possibly 90% of all gelled fracturing fluids. Carboxymethylcellulose (CMC) has little use today in hydraulic-fracturing applications. Due to uncertainity in guar availability, CMC is being recommended as an effective polymer alternative in hydraulic-fracturing applications. In order to evaluate this option, a comparative study was conducted between guar and CMC performance as gelling agents in hydraulic fracturing. CMC can be an effective alternative to guar and as this study illustrates can minimize formation and proppant pack damage. Furthermore, the critical overlap concentration, C* was determined as an indicator of crosslinkability at low polymers concentration for both guar and CMC. This study was also conducted in order to evaluate the effect of several breakers (ammonium persulfate, sodium persulfate and enzymes) on linear polymer and crosslinked gel systems degradation. Viscosity, particle size distribution and regain conductivity were measured as a function of breaker type and concentration. Design schedules of hybrid fracturing jobs performed with CMC and guar in similar completion conditions in the Permian Basin were reported.