Acid Fracturing of Power Water Injectors: A New Field Application Using Polymer-free Fluids

Samuel

2003

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TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractDifferent acid systems have been used to stimulate production and injection wells for more than a century. Several chemicals are added to the acid to enhance the efficiency of the acidizing treatments, including various types of surfactants.Surfactants play a key role in many well treatments because of their unique properties. Surfactants are used to reduce surface tension, change wettability, mobilize residual oil, and disperse corrosion inhibitors. They are also used as anti-sludge agents, emulsifiers in acid-oil emulsions, and demulsifiers. This wide spectrum of applications is due to the ability of surfactants to adsorb on various surfaces and associate in the bulk of solutions and form micellar structures. The properties of surfactants depend on the size of the head, tail length, and configuration of the tail, surface charges, ionic strength and temperature.Recent advances in surfactant technology have introduced a new class of surfactants with special characteristics useful in oilfield applications. This new class of surfactant has the ability to form viscoelastic systems, which can be used to increase viscosity of the treating fluids, without causing formation damage. These surfactants have been used in Saudi Arabian fields to enhance diversion during matrix acid stimulation, reduce leak-off during acid fracturing and to minimize losses (well control) during workover. The system proved successful to provide fracture extensions in acid fracturing applications of low temperature seawater injectors and high temperature gas wells. These surfactant systems are non-damaging and do not require sized solids to control losses, which eliminates the need for remedial acid treatments.

Section: Spe 84898mentioning

confidence: 99%

Application of a New Class of Surfactants in Stimulation Treatments

Samuel

2003

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“…Surfactantbased acids are extensively used in acid fracturing operations (Al-Muhareb et al 2003;Nasr-El-Din et al 2003b). Viscoelastic surfactants have the main advantage of being polymer-free and also require minimum amount of additives.…”

Section: Introductionmentioning

confidence: 99%

Influence of Acid-Fracture Fluid Properties on Acid-Etched Surfaces and Resulting Fracture Conductivity

Pournik

Gomaa

SPE International Symposium and Exhibition on Formation Damage Control

2010

While experimental studies have shown acid type significantly influences resulting fracture conductivity, there has been limited work on how fluid properties relate to etched fracture faces and hence the resulting conductivity. The effects of acid solutions injected into hydraulic fractures created in carbonate formations can be assessed at the laboratory scale in acid fracture conductivity tests that mimic the conditions in an actual acid fracture treatment.Many different acid systems are currently applied in acid fracturing treatments with various degrees of success. However, there is no clear understanding of the mechanisms that lead to success of a treatment. It is clear that acid properties influence and shape the success of an acid fracturing treatment. In order to develop a better methodology for design of acid fracturing treatments, the effect of acid fluid properties on the resulting conductivity and etching must be determined. A series of acid fracture conductivity tests was conducted using four commonly used acid fracturing fluids-gelled, in-situ gelled, emulsified, surfactant-based acid. Detailed rheological properties were measured in order to explain trends noted with conductivity data.Acid system influences the degree of etching and the etching pattern due to differences in chemical and physical properties of acid systems. Under our experimental conditions, viscoelastic acid generated the greatest degree of etching and best etching pattern. Majority of experiments showed differences in conductivity among acid systems tested with most optimal acid system depending on the closure stress. While viscoelastic acid generated the highest conductivity at low closure stress, emulsified acid resulted in the largest retained conductivity at higher loads for our experimental conditions. Furthermore, effluent analysis on both the leakoff and fracture flow showed that most of the fracture face etching is the result of leaked acid into the formation with minimal etching from the fracture flow acid.

“…In the recent decade, viscoelastic surfactants have been widely and successfully used in acidizing Zeiler et al 2004), acid fracturing Al-Muhareb et al 2003;Artola et al 2004;Bustos et al 2007;Fontana et al 2007;Bulat et al 2008), and hydraulic fracturing jobs (Samuel et al 1997). Usually, polymer-based acid systems will cause high friction pressures and formation damage because of residue precipitation, breakers are needed to enhance polymer degradation and make the flow back easier, and the cleanup time is lengthy.…”

Section: Introductionmentioning

confidence: 99%

Hydrolysis Effect on the Properties of a New Class of Viscoelastic Surfactant-Based Acid and Damage Caused by the Hydrolysis Products

Wang

et al. 2013

All Days

Viscoelastic surfactants (VES) have been widely used in acidizing and acid fracturing. They are used as diversion agents during matrix acid treatments and leakoff control agents during acid fracturing. At high temperatures, viscoelastic surfactants hydrolyze, resulting in phase separation after a certain time. Their viscosities significantly decrease and it is much easier for them to flow back and this causes much less damage to the formation.In this study, 4 to 8 wt% of a new VES-acid system were tested at temperature up to 250°F over hydrolysis times of 0 to 6 hours. Then the solutions were neutralized by calcium carbonate until pH reached 4.5. An HP/HT rheometer was used to measure the viscosity of the spent acids. Mass spectrometry (MS) was conducted to analyze the hydrolysis products of the VES. Coreflood tests were also conducted on Indiana limestone to determine the effect of the hydrolysis products on the permeability of these cores. Temperature was set at 250°F and flow rate at 2.5 cm 3 /s.The viscosities of all VES-acid systems remained high at the beginning of hydrolysis, which was good for acid diversion. After that, the VES acid systems experienced significant viscosity reduction because of phase separation; it became much easier for the spent acid to flow back. Coreflood experiments showed little damage caused to the Indiana limestone. MS results indicated that hydrolysis was achieved through the peptide bond. Fatty acids formed the top oil layer and amine-based molecules formed the aqueous phase. This paper will summarize and discuss the details of viscosity changes of the acid systems of this kind of viscoelastic surfactant, the damage caused by the hydrolysis products, and how this kind of viscoelastic surfactant can be used to improve the treatments.