Thomas Welton - Anionic Surfactant Gel Treatment Fluid

Document created by Thomas Welton on Feb 10, 2017
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  Publication Details (including relevant citation   information):

  Welton, Thomas Donovan, Bryant, Jason, Funkhouser, Gary P. -

  Abstract: Abstract Typical viscoelastic   surfactant gels used for gravel packing and hydraulic fracturing   have relied upon cationic, amphoteric, or zwitterionic   surfactants as their primary gelling agent, complicating the   stimulation of some wells due to wettability or formation fluid   compatibility issues. This paper describes an anionic   viscoelastic surfactant developed for fracturing and gravel   packing applications. The performance of the gel as a function of   temperature, salt type and concentration, and cosurfactant will   be presented along with the chemical structure/activity   relationship. Rheological measurements demonstrate that fluids   made with the new anionic surfactant have effective performance   over a range of conditions encountered in treating wells.   Introduction Surfactant-gelled fluids have been used for fracture   acidizing, matrix acidizing, gravel packing, frac packing, and   hydraulic fracturing since the mid-1970s.1-4 One of the perceived   benefits of these fluids is that they are considered less   damaging than polymer-based fluids. The fluid's rheology is   heavily influenced by temperature, counter ions (salts),   co-surfactants, and contamination. Because the processing of   surfactants does not yield micron-sized impurities often observed   in guar gum, and the molecular weights of surfactant molecules   are much smaller than guar molecules, surfactant gels do not form   a filter cake, and thus have higher leakoff rates into the   reservoir. Surfactant gels typically lose their viscosity by   contact with hydrocarbons or by dilution with formation fluids.   However, this often also results in an undesirable emulsion being   formed. Another potential problem of some cationic surfactant   gels is that they may adversely alter the wettability of   sandstone formations. Current gel-forming surfactants are   predominantly cationic (such as a quaternary amine) or   amphoteric/zwitterionic (such as betaine). A new class of anionic   surfactants has been discovered to form surfactant gels.5-8   Methyl ester sulfonates (MES) have been commercially available   since the mid-1960s; however, their ability to form surfactant   gels was not discovered until recently. To date, the only known   oilfield uses of MES are antisludging, dispersing, and   demulsification.8, 9 MES is prepared by the addition of sulfur   trioxide to the a-carbon of a methyl ester and subsequently   neutralized with a base (Fig. 1). There are three drivers for   commercialization of MES. First, it is less expensive than   a-olefin sulfonate. Second, it is derived from renewable   resources such as palm kernel oil. Finally, it has a better   environmental profile than many surfactant gels because it is   biodegradable and exhibits low aquatic toxicity.10 Rheology   Preliminary rheological studies were performed on three   laboratory samples prepared as follows: Sample 1   Mixing water   with an MES surfactant B in an amount of approximately 5% by   weight of the sample with approximately 5% sodium chloride, with   the final sample pH not adjusted. Sample 2   Sample 1 in alkali   form, with the pH adjusted to approximately 10 using sodium   hydroxide. Sample 3   Sample 1 in acidic form, with the pH   adjusted to approximately 4 using hydrochloric acid. Once the   samples were prepared, rheological responses of each fluid were   measured using a Haake RheoStress RS150 stress-controlled   rheometer fitted with a 60-mm diameter, 2  cone and plate. The   temperature was held constant at 77 F. A constant frequency (1   Hz) oscillatory stress sweep was performed over a broad stress   range to obtain the storage modulus (G'), loss modulus (G''), and   phase angle (d). Results are shown in Figs. 2, 3, and 4 for the   unadjusted, alkaline, and acidic samples, respectively. In the   linear viscoelastic limit, the storage modulus of the sample   where the pH was unadjusted is about 20 Pa. Significantly higher   degrees of elasticity were observed for the two samples that had   the pH adjusted, because the storage moduli for the alkali and   acidic solutions were approximately 38 Pa and 55 Pa,   respectively.

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