Recent Advances in Viscoelastic Surfactants for Improved Production from Hydrocarbon Reservoirs

Abstract

Viscoelastic surfactants (VES) are used in upstream oil and gas applications, particularly hydraulic fracturing and matrix acidizing. A description of surfactant types is introduced along with a theoretical description of how they assemble into micelles, what sizes and shapes of micelles can be formed under different conditions, and finally how specific structures can lead to bulk viscoelastic solution properties. This theoretical discussion leads into a description of the specific VES systems that have been used over the last twenty years or so in improved oil recovery for upstream applications.VES-based fluids have been used most extensively for hydraulic fracturing. They are preferred over conventional polymer-based fracturing fluid systems because they are essentially solids-free systems which have demonstrated less damage to the reservoir rock formation. Important advancements in VES have been made by introducing "pseudo-crosslinking agents" such as nanoparticles to enhance the viscosity. Fracturing fluid systems based on VES have also been improved recently by developing internal breakers to lower their viscosity in order to flow back the well. The flexibility of VES-based fluids has been demonstrated by their application as foamed fluids as well as their incorporation with brine systems such as produced water.A second key area that has benefited from VES-based systems is matrix acidizing carbonated-based reservoirs. The viscosity of these VES-based fluids is mostly controlled by pH where, at low pH (low viscosity), the acid system flows easily and invades pore spaces in the formation. During acidizing, the acid is spent, and the pH and viscosity increase. Because the spent acid has higher viscosity, fresh acid is diverted to low permeability un-contacted zones and penetrates the rocks to form wormholes. A number of experimental studies and field applications to these effects have been performed and will be described here.In order for VES-based fluids to play a more prominent role in the field, inherent limitations such as cost, applicable temperature range, and leak-off characteristics will need to continue to be addressed. If we can efficiently and economically overcome these issues, VES-based fluids offer the industry an excellent clean, non-damaging alternative to conventional polymer-based fluids.

A systematic rheological study of alkyl amine surfactants for fluid mobility control in hydrocarbon reservoirs

“…Employed in this study, a classical qualitative model called Israelachvili's packing parameter, ''P,'' characterizes the micellar morphology where thermodynamics and free energy conditions of the system provoke micellar structural transformations (Collura et al 2001;Hull et al 2015;Raghavan 2009). This model's packing parameter value, ''P'' in Eq.…”

“…Depending on internal and external parameters, the morphology can transition from one division to another. When the micelles organize into cylindrical aggregates or entangle wormlike structures, the solution transforms into a viscoelastic state (Hull et al 2015;Koehler et al 2000).…”

Gemini Surfactant with Unsaturated Long Tails for Viscoelastic Surfactant (VES) Fracturing Fluid Used in Tight Reservoirs

“… 30 Compared to the conventional single-chain surfactants, gemini surfactants, 31 , 32 a class of superior surfactants comprising two amphiphilic moieties linked by a spacer group, could satisfy the request of proppant transportation for fracturing fluid more easily. 15 , 26 There are better reductions of flow resistance 33 and heat/shear resistance 34 , 35 in the VES fracturing fluid prepared with gemini cationic surfactants. The contour length of micelles proposed by Magid 36 is a crucial parameter positive to the micellar morphology 36 and the capability of proppant transportation, following eq 1 : 37 where L is the contour length of micelles, ϕ is the volume fraction of surfactant, E c is the end-cap energy of micelles, k is the rate constant, and T is the absolute temperature.…”

“… 15 − 18 Nevertheless, the poor thermal stability of VES fluid leads to a significant viscosity reduction in high-temperature environments, 19 , 20 which limits the proppant transportation capability severely. 21 , 22 To obtain the effective transport of proppant at high temperatures, a high dosage (usually 3–5 wt %) of surfactant is generally required in VES, 23 − 26 which results in the high cost for the immense surfactant consumption and restricts the extensive application of VES fracturing fluids. 6 Therefore, it is necessary to develop novel VES fracturing fluids with low surfactant concentrations that have the favorable performance at high temperatures.…”

Effects of Rheological Behavior of Viscoelastic Surfactants on Formation Damage in Carbonate Rocks

“…VES result in a rapid viscosity built up due to the entanglement of these rod‐like micelles. VES are being used in the petroleum industry for matrix stimulation and enhanced oil recovery (EOR) (Adejare and Nasralla, ; Aoudia et al, ; Hull et al, ; Kamal et al, ; Yu et al, ). Matrix stimulation is often needed in limestone and dolomite reservoirs to generate wormholes.…”