No abstract

The viscoelastic surfactants (VES)-based acid diverters are frequently used to divert acid flow from highpermeability layers into low-permeability for enhanced overall productivity of the treated well. In general, an optimum VES-based system possesses advantages of decrease in absorption loss, damage of reservoir, and improved adaptability of active agents to high salinity. Herein, we report the synthesis of three new zwitterionic gemini surfactants (1-3) and previously known amidosulfobutaine (C 18 AMP3SB) has been accomplished for the investigation of diverting acid performance. The synthesis of these surfactants was achieved by the amidation of the acid chlorides of commercially available fatty acids with 3-(dimethylamino)-1-propylamine followed by subsequent reactions with appropriate sultone or ethyl 4-bromobutanoate. The synthesized surfactants were well characterized by spectroscopic methods including IR and NMR spectroscopy. The thermogravimetric analysis (TGA) results suggested that surfactants (1-3) and C 18 AMP3SB possess excellent thermal stability, with no appreciable loss of mass up to 300 C. The viscosity measurements of the neat surfactants (1-3) and C 18 AMP3SB were performed under various temperatures, in the presence of different concentration of calcium chloride salt with the aid shear viscosimetry. The analysis revealed that the viscosity of neat C 18 AMP3SB increases with increase in concentration of CaCl 2 . With 10% CaCl 2 solution, the viscosity was increased from 7.5 to 33.55 cPs, whereas in 20% CaCl 2 the viscosity reached to 102 cPs with rise in temperature from ambient to 90 C. Moreover, the viscosity of neat surfactants (1-3) did not exhibit any appreciable viscosity change under the experimental conditions. However, the mixture of surfactants (1-3) each in combination with C 18 AMP3SB (1:1) displayed significant upsurge in the viscosity, up to more than 10 folds.

Resin coated proppants are widely used in fracturing applications. They serve two purposes namely to increase the strength of proppant material to withstand closure stresses and to mitigate any proppant flowback. Typically, resins used for proppant coatings are made up of hydrophobic polymers and are inherently incompatible with the aqueous fracturing fluid. To avoid any slugging issues due to this incompatibility, the coated resins are typically semi-cured. The coating process needs to be undertaken during proppant manufacturing and adds to the overall cost of the proppants used. In this paper we showcase the development of novel insitu generated hybrid materials that enhance the proppant strength. Moreover, the resins used for proppant coating are introduced as a water external emulsion, thus making them compatible with the aqueous fracturing fluids. We show that by using a solid resin based emulsion system as proppant coating material we could introduce this system on-the-fly along with the fracturing fluid without facing any incompatibility issues between the hydrophobic resin and the aqueous fracturing fluid. We further show that by using tactoid based filler materials suspended with the emulsified resin we could tremendously enhance the overall mechanical strength of the proppants. The solid resin above the temperatures of 60°C melts and starts to intercalate into the layered tactoid fillers. The process of intercalation is driven by mechanical shear as the fracturing fluid is pumped downhole, as well as by thermodynamics of intercalation. Specific structural modifications were utilized to increase the entropy of the layered tactoids, facilitating the intercalation of resin. Increased intercalation of the resin inside confined spaces of the tactoid overcame the Van der Waals forces that hold the tactoid layers together. As the tactoid layers separated they formed an exfoliated structure of high aspect ratio filler with nanoscale dimensions of around 1nm thickness. The high aspect ratio nanofillers uniformly dispersed in the resin matrix ensured effective load transfer from the matrix thereby tremendous increase in the overall mechanical strength of the resin coated proppants. We studied the mechanical properties by evaluating the compression strength of the resin nanocomposite coated proppants in comparison with the pristine resin coated and uncoated proppants. The mechanical strength enhancements in the nanocomposite coated proppants were clearly evident from this study. Structural evaluation of nanocomposites showed uniform dispersion of the fillers in epoxy matrix could be achieved whilst generating the nanofillers insitu. The viscoelastic properties of the nanocomposite based coating were also investigated and showed better mechanical behavior over those of pristine resin coatings. Novelty of this paper of newly developed proppant coating nanocomposite material is in situ generation of the nano fillers and on the fly deployment of the resin coating material along with fracturing fluid due to enhanced compatibility.

Gelled acid systems based upon gelation of hydrochloric acid (HCl) are widely used in in both matrix acidizing and fracture acidizing treatments to prevent acidizing fluid leak-off into high permeable zones of a reservoir. The gelled up fluid system helps retard the acid reaction to allow deeper acid penetration for hydrocarbon productivity enhancement. The in-situ gelation is typically achieved by using crosslinked polymers with the acid. Conventional in-situ crosslinked gelled acid systems are made up of polyacrylamide gelling agent, iron based crosslinker and a breaker chemical in addition to other additives, with the acid as the base fluid. However, the polymer-based systems can lead to damaging the formation due to a variety of reasons including unbroken polymer residue. Additionally, the iron-based crosslinker systems can lead to scaling, precipitation and or sludge formation after the acid reacts with the formation, resulting in formation damage and lowering of hydrocarbon productivity. In this paper we showcase a new nanoparticles based gelled acid system that overcomes the inherent challenges faced by conventional in-situ crosslinked gelled acid systems. The new system can work in 5 to 20 % HCl up to 300°F. The new system does not contain any polymer or iron based crosslinker that can potentially damage the formation. It comprises nanoparticles, a gelation activator, acidizing treatment additives along with HCl. The new in-situ gelled acid system has low viscosity at surface making it easy to pump. It gels up at elevated temperatures and pH of 1 to 4, which helps with diverting the tail end acid to tighter or damaged zones of the formation. We demonstrate that the viscosification and eventual gelation of the new system can be achieved as the acid reacts with a carbonate formation and the pH rises above 1. As the acid further reacts and continues to spend there by increasing the pH beyond 4, the gel demonstrates reduction of viscosity. This assists in a better cleanup post the acidizing treatment. Various experimental techniques were used to showcase the development of the nanoparticle based acid diversion fluid. Static and dynamic gelation studies as a function of time, temperature and pH are reported. The gelation performance of the new system was evaluated at temperatures up to 300°F and discussed in the paper. Comparative performance of different types of gelation activators on the gelation profile of the nanoparticles is evaluated. It is also shown that the gelation and viscosity reduction is entirely a pH dependent phenomenon and does not require any additional breaker chemistry, and therefore provides more control over the system performance. The novelty of the new gelled acid system is that it is based upon nanoparticles making it less prone to formation damage as compared to a crosslinked polymer based system.

Gelled acid systems based upon gelation of hydrochloric acid (HCl) are extensively used in both matrix acidizing and fracture acidizing treatments to prevent acidizing fluid leak-off. The gelled-up fluid system helps retard the acid reaction to allow deeper wormhole propagation. Conventional in-situ crosslinked gelled acid systems consist of a polyacrylamide polymer, a crosslinker (such as iron-based crosslinker), a chemical breaker, other additives, along with acid. However, these systems can lead to damaging the formation due to several reasons including unbroken polymer residue or scaling, resulting in lowering of hydrocarbon productivity. To mitigate these drawbacks, we have developed a self-breaking, formation damage-free, novel nanoparticles based gelled acid system to replace the polymer based gelled acid system. The new gelled acid system is based on, surface modified nanoparticles to make them compatible in acidic environment, a gelation activator, acidizing treatment additives along with HCl to overcome the challenges the conventional systems face. The new system can work with up to 28& of HCl up to 300°F with low viscosity at surface, making it easy to be pump. As the acid spends due to reaction with the formation the pH of the fluid transitions from acidic to basic pH. The gelation phenomenon of the new system is controlled by the increasing pH. As the pH increases beyond pH 1 gelation of the nanoparticles occurs thus gelling up the acidic fluid. As the pH further continues to rise beyond pH 4 the nanoparticles lose their capability to gel up and the fluid viscosity decreases to pre-gelation level, facilitating easy post treatment flow back. A systematic experimental protocol was followed to develop the new system that is documented in this paper. It is shown that the gelation properties are pH dependent phenomenon providing the critical control over the gelation time and avoiding any premature gelation during pumping the treatment. The effectiveness of the system by not damaging the formation was investigated using regain permeability studies. The new system showed excellent regain permeability. The obtained data confirmed several advantages of the new system over conventional polymer based gelled acid systems. Gelation experiments were performed to gather a better understanding of the gelation mechanism and also to get effective control on the gelation and break properties. The uniqueness about the new system is that, it is formation damage free without the need to use polymers or iron based cross-linkers that may lead to potential damage mechanisms.