It is a great challenge to divert acid into untreated zones in a thick, heterogeneous, and high permeability sandstone formation. The heterogeneity can be created by hydraulic fracturing, acidizing, or the nature of the reservoir. Common diverting agents do not work well in these situations. In high permeability porous media, foam has the tendency to segregate, gaseous phase will occupy smaller pores while the aqueous phase occupies the larger pores1 . Due to the relative permeability effect, the higher permeability streaks becomes the preferable path for acid treatment fluids2 . Therefore, limited effective diversion can be achieved by foam. Other diverting agents rely on particulate matter or polymer solution to plug off thief zones temporarily. However, the invasion of the undissolved particles and polymer residue can cause further formation damage.

Owing to its rheological properties, and its lack of solids, Visco-Elastic-Surfactant diverting agents (VESDA) have been proven to be effective for acid diversion in carbonate formations3 , where large flow channels are generated due to acid-rock reaction. This current study extends the application into diversion in high permeability, highly heterogeneous sandstone formations. Throughout this paper, the term VESDA is used to refer to the VES diverting agent. Laboratory tests have shown that VES is capable of increasing the flow resistance in the high permeability rock (simulated by a proppant pack) and will divert treatment fluid into the low permeability sandstone matrix. The process was more efficient if multiple stages of alternating VES and acid were used. Field case histories in Gulf of Mexico are also presented in this study to demonstrate the effectiveness of the VES material for acid diversion in the highly permeable and heterogeneous sandstone reservoirs.

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