Propagation of Cross-linkers Used in In-Situ Gelled Acids in Carbonate Reservoirs

Nasr-El-Din, H.A.; Taylor, K.C.; Al-Hajji, H.H.

doi:10.2523/75257-ms

Cited by 35 publications

(12 citation statements)

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“…17,18 Based on laboratory data, the effectiveness of in-situ gelled acid in diversion was recently questioned. 2,3 Foam diversion is a readily accepted technique, however there are concerns when the foam has a short half-life.…”

Section: Foam Versus In-situ Gelled Acidmentioning

confidence: 99%

Enhancement of Stimulation Treatment of Water Injection Wells Using a New Polymer-Free Diversion System

Safwat

Nasr‐El‐Din

Dossary

et al. 2002

Abu Dhabi International Petroleum Exhibition and Conference

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractVertical seawater injectors for a carbonate reservoir in Saudi Arabia have an injection zone (open hole) of approximately 200 ft. This reservoir has drastic permeability variations. Acid stimulation without proper diversion normally results in undesirable stimulation of the high permeability streaks. Therefore, acid diversion plays a key role in improving both the post-acid, well-injectivity and injection profile.Various diverting agents have been used to improve the acid distribution during acid injection, including wellbore gels, foams and in-situ gelled acids. The use of polymers is an excellent means of diversion. 1,2 However, evaluation of polymeric systems has demonstrated formation damage due to residual polymer, which is considered unacceptable, especially for water injection wells. 3 Conventional foams have also been tested with good success.In the present study, the use of a polymer-free viscoelastic surfactant (VES) as a diverter system is investigated and compared with in-situ gelled acid and foams. The VES is a twocomponent system, and in the presence of salts, the surfactant molecules associate to form rod-like micelles. These micelles can entangle with each other and form a three dimensional network, responsible for the high viscosity of the system. 4,5 This non-damaging "surfactant gel" can be broken completely by injecting mutual solvent or injection water. This added advantage eliminates the need to flow back the well following acid treatments.Laboratory studies demonstrated up to 2-fold increase in viscosity and nearly 20-fold increase in foam stability compared to foams containing polymers. The properties of VES solutions are independent of the salinity and pH of the mixing water.Bullheading the acid enables the operator to pump these treatments at high rates, which are needed in some cases. Pumping pressure, post-acid injectivity history and injection flow profile of several seawater injectors indicate good stimulation results and better acid diversion across the whole target zone.This paper presents the first application worldwide on the use of VES technology in water injection wells. A total of six stimulation treatments were performed using this technology, one treatment using coiled tubing (CT) and five by bullheading.The VES technology provides a solution for heterogeneous carbonate reservoirs, and eliminates formation damage induced by the polymers present in the conventional diversion systems. Stimulation using the VES system on six wells resulted in an injection increase of more that 45,000 bbl of water per day, much higher than similar treatments where conventional foams were used.

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Section: Foam Versus In-situ Gelled Acidmentioning

confidence: 99%

Enhancement of Stimulation Treatment of Water Injection Wells Using a New Polymer-Free Diversion System

Safwat

Nasr‐El‐Din

Dossary

et al. 2002

Abu Dhabi International Petroleum Exhibition and Conference

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“…The solution will vaporize as a mixture of acid and alcohol; this vaporization of acid/alcohol blend occurs in the gas phase of produced fluids. 3 The use of mutual solvent accelerates breaking both viscoelastic fluids, its use is recommended especially in dry gas wells in which the content of liquid hydrocarbons can be minimal. Because of the low content of liquid hydrocarbons, emulsion tests with the native condensate are not required.…”

Section: Acid Fracturing Challenges In Veracruz Wellsmentioning

confidence: 99%

Nondamaging Viscoelastic Surfactant-Based Fluids Used for Acid Fracturing Treatments in Veracruz Basin, Mexico

Artola

Alvarado

Huidobro

et al. 2004

SPE International Symposium and Exhibition on Formation Damage Control

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFor the last eight years acid fracturing stimulation has been performed in the Veracruz basin to increase gas production in naturally fractured carbonate formations. Several techniques have been proved to enhance the results of these jobs, including the diverting technique and the application of nondamaging viscoelastic fluids technology specifically a selfdiverting viscoelastic based acid system and a polymer-free viscoelastic surfactant gel for fracture initiation and propagation. This paper presents the results of successful acid fracturing treatments recently performed using nondamaging viscoelastic surfactant-based fluids to increase gas production from naturally fractured carbonate formations.Most of the wells drilled and completed in the carbonate formations of cretaceous age in Veracruz basin do not flow naturally because of low matrix permeability and drilling/completion fluids damage. Therefore, acid fracturing treatments are necessary to produce these wells at economical rates.The objective of these treatments is to increase gas production by creating a deeply etched fracture that will bypass the damaged zone and connect to the network of natural fractures and/or fissures. The etched fracture length affects well performance in low-permeability reservoirs; increased fracture length should result in greater production response. The use of nondamaging viscoelastic fluids is necessary to obtain longer effective etched fractures. Combining this with the properties of a viscoelastic diverting acid will significantly increase fracture conductivity as well as the effective stimulation of all perforated intervals.The fluids were combined by using a pumping technique that consists of alternating stages of nonreactive fluids, reactive fluids and diverter fluid to reduce wormhole creation at the nearwellbore area and increase etched fracture length.Four field cases are presented in this paper. In three, multiple intervals were treated, resulting in longer etched fractures as deduced from after-treatment production response and radioactive tracer logs. In the fourth case, not all the intervals were effectively stimulated because diversion was not used.

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“…This is especially true in tight formations. [15][16][17] Currently, visco-elastic surfactants have been used in many oil field applications. 18 -22 The main advantage of these systems is that they are polymer-free.…”

Section: Previous Stimulation Acidsmentioning

confidence: 99%

Acid Fracturing HT/HP Gas Wells Using a Novel Surfactant Based Fluid System

Nasr‐El‐Din

Saad

Al-Muntasheri

et al. 2003

Proceedings of SPE Annual Technical Conference and Exhibition

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During acid fracturing of carbonate reservoirs, the acid dissolves the rock, creating wormholes which increase fluid loss. Excessive fluid loss lowers the net pressure in the fracture limiting fracture extension, and adversely affects the conductivity of the fracture. To overcome this problem, multiple stages of polymer pads are usually pumped in acid fracturing treatments to reduce leak-off. In addition, synthetic polymers are commonly added to the acid to produce gelled or in-situ gelled acids. The objective of adding these polymers is to reduce leak-off, by increasing the viscosity of the acid. This in turn reduces the rate of mass transfer of the acid to the rock surface. However, several studies have shown that these polymers can cause formation damage. Moreover, the crosslinker can precipitate in the formation causing further damage. Efficient mixing of synthetic polymers in the field is also a concern, especially when the polymers are present in a solid form.To overcome problems associated with polymeric fluids, polymer-free fluids were used for the first time to acid fracture several vertical wells in a deep gas reservoir in Saudi Arabia. The acid fracture treatments consisted of several stages including: viscous pads, emulsified acid, in-situ acid and an inhibited acid. A visco-elastic surfactant system replaced the polymers used in the pad and the leak-off control acid (28 wt% HCl). Calcium chloride produced from acid reactions with the carbonate rock viscosifies the acid in-situ, reducing leak-off volume. ResultsThe pressure response to acid f racture treatments clearly indicates that the surfactant-based system is very effective in controlling acid leak-off during the treatment in wells with a bottom hole temperature of nearly 260 o F. Good leak-off control did help in maintaining a constant pumping rate throughout the treatment. Significant increases in both gas production and flowing wellhead pressures were achieved utilizing this new system. In addition, pumping operations were simplified by continuous mixing of the fluids. The nondamaging nature of the system enhanced production rates above expectations.

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Propagation of Cross-linkers Used in In-Situ Gelled Acids in Carbonate Reservoirs

Cited by 35 publications

References 0 publications

Enhancement of Stimulation Treatment of Water Injection Wells Using a New Polymer-Free Diversion System

Enhancement of Stimulation Treatment of Water Injection Wells Using a New Polymer-Free Diversion System

Nondamaging Viscoelastic Surfactant-Based Fluids Used for Acid Fracturing Treatments in Veracruz Basin, Mexico

Acid Fracturing HT/HP Gas Wells Using a Novel Surfactant Based Fluid System

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