Abstract
Hydraulic fracturing operations target enhancing the productivity of tight formations through viscous fluid injection to break down the formation and transport proppant. Crosslinked polymers are usually used for desired viscoelasticity of the fracturing fluid; however, viscoelastic surfactants (VES) became a possible replacement due to their less damaging impact. To design a fracturing fluid with exceptional rheological and thermal stability, we investigated mixing zwitterionic VES with carboxymethyl cellulose (CMC), hydroxyethylcellulose (HEC), or a poly diallyl dimethylammonium chloride (DADMAC) polymers. As a base fluid, calcium chloride (CaCl2) solution was prepared with either distilled water or seawater before adding a polymer and the VES. A Chandler high-pressure, high-temperature (HPHT) viscometer was used to conduct the viscosity measurements at a shear rate of 100 1/s. It has been found that adding 1% CMC polymer to 9% (v/v) VES increases the viscosity more compared to 10% (v/v) VES at reservoir temperatures of 143.3 °C. On the other hand, adding only 1.0% of HEC to 9% (v/v) VES doubled the viscosity and proved more effective than adding CMC. HEC, nevertheless, reduced the system stability at high temperatures (i.e., 148.9 °C). Adding DADMAC polymer (DP) to VES increased the system viscosity and maintained high stability at high temperatures despite being exposed to saltwater. CaCl2 concentration was also shown to affect rheology at different temperatures. The improved viscosity through the newly designed polymer can reduce chemical costs (i.e., reducing VES load), making it more efficient in hydraulic fracturing operations.
Highlights
Hydraulic fracturing operations are applied to enhance the recovery of hydrocarbons from low permeability formations
We investigate the influence of different polymer additives on the viscosity of the viscoelastic surfactants (VES) fluid depending on their charge and functional groups while maintaining the high-temperature stability and good compatibility of the fluid at high salinity
Polymer selection was based on their compatibility and type where carboxymethyl cellulose (CMC) is anionic, and hydroxyethyl cellulose (HEC) is neutral; they are both based on cellulose while diallyl dimethylammonium chloride (DADMAC) is a cationic polymer
Summary
Hydraulic fracturing operations are applied to enhance the recovery of hydrocarbons from low permeability formations. VES fracturing fluids are characterized as micelles or vesicles based on the shape of surfactant aggregation in water. The VES has a very low molecular weight in comparison to crosslinked polymers It generates viscosity and forms worm-like micelles or vesicles in response to physical interactions and loses this viscosity when the physical interaction changes. The aggregation size in vesicle-based VES is much larger than worm-like micelles, which results in a large surface area. It does not continuously lose and reform shape, making it more stable [16]. The micelles become warm-like, forming a stable network structure which results in viscosity increase; it is known as a viscoelastic surfactant (VES). MggCCl2l2aannddCCaaCCl2l2sshhoowweedd aannininccrereaaseseininsosloulutitoinonelealsatsictiictyitymmoroertehtahnaNn aNCal,CKl,CKl,Caln, danNdHN4HCl4C[1l4[]1. 4F]o. rFVorEVS EmSicmelilcaerllianr CinaBCra2Barn2danCdaCCla2Cblr2inbersin, aeds,daidngdiMnggOMogrOZonrOZnnaOnonpaanrotpicalersticinlecsreianscerdeatsheedrmthaelrsmtaablilsittaybailnitdy vainscdovsiitsycoastivtyaraitedvasrhieedarsshpeeaerdssp[e2e3d]s. [23]
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