Use of Viscoelastic Surfactant-Based Diverting Agents for Acid Stimulation: Case Histories in GOM

Abstract

Viscoelastic-surfactant (VES)-based diverting products have been used successfully in matrix acidizing in the Gulf of Mexico (GOM) in recent years. The uses of VES diverters range from remedial matrix-acid or nonacid-cleanup treatments to use before gravel-or frac-packing operations to clean up long intervals after perforating. Success or failure of these treatments is often related to the efficiency of diverting agents, especially for acid treatments on wells with long, heterogeneous intervals or multiple-zone completions. A VES diverting agent is of particular interest to remedial treatments of frac-/gravel-packed wells, because damage to the near-wellbore area and completion should be minimized for optimum production. Laboratory studies and field applications have demonstrated the nondamaging properties of a VES fluid.This paper reviews the properties of the vesicular-type VES diverting fluid, reviews the operational considerations, and presents several case histories with VES diverting agents in the GOM. The bottomhole static temperatures (BHSTs) of these cases range from 140 to 290°F for both gas and oil wells. With an internal breaker system, the diverter does not require contact with formation fluid, brine, or acid to clean up and provide optimum production. In some cases, as many as four stages of diverters were pumped in the treatment, and successful diversion was observed for each stage. The paper outlines field-operational considerations and detailed fluid properties, which were tailored to specific well conditions and formation characteristics. Details and pressure responses of the treatments are discussed.

Viscosity-Reducing Agents (Breakers) for Viscoelastic Surfactant Gels for Well Stimulation

“…It has been shown through coreflood studies that external breakers do not efficiently reduce the viscosity of the VES gel formed in the cores. , Moreover, internal breakers have been shown to ensure the efficient cleaning of cores or proppants. ,,, Furthermore, VES gels take around 4–7 days to be cleaned up by bacteria . Lastly, internal breakers are necessary for gas wells that have minimal or no liquid hydrocarbons to reduce the viscosity of the VES gels. ,, …”

“…Wormlike micelles (WLMs) form with an increase in the concentration, and they become entangled with the continuous rise in the concentration. It is the entanglement of WLMs that gives VES gels their high viscosity. ,, In some reservoir applications, vesicles are formed . To transition from spherical micelles to WLMs and vesicles, the surfactant molecules need to be closely packed. ,, …”

“…As for the use of internal breakers, Zeiler et al reported the use of an internal breaker alongside a VES to treat four wells in the Gulf of Mexico. They used an internal breaker because laboratory results showed internal breakers brought about a better performance than external breakers, especially at low bottom hole static temperatures.…”

Modeling Flow of Chelating Agents during Stimulation of Carbonate Reservoirs

“…In such cases diverting agents should be used to stimulate the formation effectively. Mechanical and chemical diverters such as ball sealers, polymers, and surfactants have been used to redirect flow to low permeable zones (Zeiler et al 2006).…”

Impact of Hydrolysis at High Temperatures on the Apparent Viscosity of Carboxybetaine Viscoelastic Surfactant-Based Acid: Experimental and Molecular Dynamics Simulation Studies

“…In recent years, viscoelastic surfactants have been successfully applied in oilfield acid fracturing fluids (Al-Muhareb et al 2003;Artola et al 2004;Bustos et al 2007;Fontana et al 2007;Bulat et al 2008), fluidloss pills ) and matrix-acidizing fluids Al-Mutawa et al 2005;Zeiler et al 2006;Liu et al 2009;Nasr-El-Din et al 2009a, b). VES-based fluids were used in these applications because, first, they can serve as substitutes to polymers as fluid viscosifiers.…”