Toward Zero Damage: New Fluid Points the Way

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIt is well known that increasing the ionic strength of aqueous solutions containing certain categories of anionic surfactant can produce interesting behaviors. The molecules of some surfactants cluster together forming spherical micelles. However, a select few surfactants, with particular molecular structure, undergo a remarkable transition from spherical micelles to larger, anisometric aggregates. The size, flexibility and extent of interaction of these aggregates all have an influence on the rheological properties of such solutions, producing very substantial viscosities at low shear rates.Conversely, when these surfactant solutions encounter other chemical species, particularly relatively non-polar materials, like alcohols, glycols and hydrocarbons, this affects the shape and structure of the micelles. As a result, the phase behavior is altered and the solution undergoes a dramatic reduction in viscosity.Proper selection of a surfactant allows its application in several oil field treatments such as reservoir gravel packing, frac-packing, fracturing, brine thickening, non-damaging temporary plugs and also for reservoir flooding and water shut-off.The main advantage of these solutions, compared to conventional polymer systems, is the potential for reduced formation and proppant pack damage. However, there are many other advantages. These fluids exhibit unexpectedly low high-shear viscosities resulting in low friction pressures, even in small tubular. In addition, due to the very low viscosity of the broken fluid, faster load recovery of injected fluids is possible. A final benefit offered by these systems is operational simplicity at the well site, since there is no need to "pre-gel" tanks ahead of the treatment. This paper describes the chemistry involved to develop these viscous solutions and their applications in different treatments in the field.

Recent Advances in Viscoelastic Surfactants for Improved Production From Hydrocarbon Reservoirs

“…It is considered to be more environmentally friendly than other surfactant gels because it is derived from renewable resources such as palm kernel oil, is biodegradable, and is less toxic. Several fracturing treatments were performed in South America with an environmentally friendly anionic surfactant (EHAC) at 4 vol% (Di Lullo et al 2001) and were reported to improve production in three case studies.…”

“…These are elongated rodlike micelles that are long and flexible and can entangle in solution, imparting viscoelastic properties to the fluid. Detailed structural, chemical, and behavioral characteristics of wormlike micelles have been recently reviewed in the chemical literature (Dreiss 2007). The review provides an extensive list of surfactant systems that have been reported to form wormlike micelles and the corresponding methods used to characterize these fluids, such as cryo-transmission electron microscopy (cryo-TEM), rheology, static light scattering, and small-angle neutron scattering.…”

“…The inverse of the crossover frequency of G 0 and G 00 is the relaxation time s R . This model has been applied to a large number of viscoelastic-micelle solutions and is generally considered a good indication that wormlike micelles are present (Dreiss 2007). Under steady shear flow, wormlike micelles exhibit a lowshear Newtonian plateau, which is characterized by a zero-shear viscosity: g 0 ¼ G 0 s R : However, when the critical shear rate _ c c is exceeded, the wormlike-micelle solution undergoes strong shear thinning.…”

Lessons Learned and Guidelines for Matrix Acidizing With Viscoelastic Surfactant Diversion in Carbonate Formations

“…Hydrocarbons (diesel, oil, or condensate) and mutual solvents (ethylene glycol monobutly ether) act as breakers when they come in contact with viscoelastic surfactants. 7,8 Laboratory testing has proven that a lower concentration of viscoelastic surfactant can provide the required viscosity to achieve effective diversion. A lower concentration of viscoelastic surfactant will facilitate cleanup at lower bottomhole temperatures without a breaker and obviously make it a more cost effective material.…”

“…The entanglement of these micelles results in a 3-D structure, which produces substantial viscosity to the spent acid, especially at low shear rates. 7,8 …”