A Novel Stimulation Technique for Horizontal Openhole Wells in Carbonate Reservoirs—A Case Study in Kuwait

Liu, Hai; Coston, Chad Philip; Yassin, Mohamed Ibrahim; Uddin, Shahab; Al-Dhafeeri, Fahad M.

doi:10.2118/105127-pa

Cited by 7 publications

(1 citation statement)

References 11 publications

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“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Yan

Wang

et al. 2012

SPE Journal

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Carboxybetaine viscoelastic surfactants have been applied in acid diversion and fracturing treatments in which high temperatures and low pH are usually involved. These surfactants are subjected to hydrolysis under such conditions because of the existence of a peptide group (-CO-NH-) in their molecules, leading to changes in the rheological properties of the acid. The objective of this paper is to study the impact of hydrolysis at high temperatures on the apparent viscosity of carboxybetaine viscoelastic surfactantbased acids, and propose the mechanism of viscosity changes by molecular dynamics (MD) simulations.Surfactant-acid solutions with different compositions (surfactant concentration varied from 4 to 8 wt%) were incubated at 190 F for 1 to 6 hours. Solutions were then partially spent by CaCO 3 until the sample pH was 4.5, and the apparent viscosity was measured using a high-temperature/high-pressure (HT/HP) viscometer. To understand the mechanism for viscosity changes on the molecular level, MD simulations were carried out on spent surfactant-acid aqueous systems using the Materials Studio 5.0 Package.It was found that short-time hydrolysis at high temperatures (for example, 1 to 2 hours at 190 F) led to a significant increase in surfactant-acid viscosity. However, after incubation for 3 hours, phase separation occurred and the acid lost its viscosity. Simulation results showed that viscosity changes of amido-carboxybetaine surfactant acid by hydrolysis at high temperatures may be caused by different micellar structures formed by carboxybetaine and fatty acid soap, its hydrolysis product. The optimum molar ratio of amido-carboxybetaine and fatty acid soap to form wormlike micelles was found to be nearly 3:1 from our simulations.Our results indicate that hydrolysis at high temperatures has a great impact on surfactant-acid rheological properties. Short time viscosity build-up and effective gel breakdown can be achieved if surfactant-acid treatments are carefully designed; otherwise, unexpected viscosity reduction and phase separation may occur, which will affect the outcome of acid treatments.

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Section: Introductionmentioning

confidence: 99%

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

Yan

Wang

et al. 2012

SPE Journal

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Combination of Chemical Diverters and Degradable Fiber Technology Enhances the Success of Stimulation in Complex Carbonate Environments

et al. 2009

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Due to damage caused by drilling and completion operations, most wells in the Jurassic carbonate reservoirs in North Kuwait require acid stimulation after perforating to either recover or enhance the well productivity. To date, production responses after stimulation treatments have been mixed, depending on the formation, the type of treatment and the volume and the chemistry of stimulation fluids. Additionally post-stimulation production logging surveys in many wells typically have shown poor stimulation efficiency with only a short perforation interval contributing to a majority of the production. Thus, it becomes crucial to develop general engineering guidelines and address treatment diversion issues for future stimulation work. This paper presents an engineering process for optimizing matrix stimulation and acid fracturing treatments according to laboratory tests and well performance evaluation in more than 20 wells in the deep Jurassic carbonate reservoirs in Kuwait. The paper also introduces a new stimulation technique that combines chemical diversion (viscoelastic surfactant based diverting acids) and degradable fiber technology to enhance leakoff control and diversion capability of the chemical solution into the complex naturally fractured carbonate formations. The technique improves leakoff control into large natural fractures, dominant wormholes and high permeability zones, and results in deeper acid penetration and more effective vertical coverage. The degradable fibers completely decompose with time and temperature after the treatment has been pumped. Field results have shown significant improvement of post-stimulation production after the general engineering guidelines were implemented. Application of this new stimulation technique has been evaluated through the production surveys and performance before and after the treatment. Initial results on the first well showed an eightfold increase in the productivity index. Background The North Kuwait Jurassic Fields include Sabriyah (SA), Raudhatain (RA), Northerwest Raudhatain (NWRA), Umm Niqqa (UN), Bahrah (BH) and Dhabi (DA) (see Fig. 1). Target reservoirs include the Jurassic carbonates of Middle Marrat (MM) and Najmah/Sargelu (NJ/SG) formations with TVD of 14,000–15,000 ft. Reservoir pressure and temperature are about 11,000 psi and 275°F respectively. The area is structurally very complex with NW-SE and NE-SW trending faults that tend to create different compartments. The depositional setting ranges from deep to shallow marine, including a supratidal environment (sabkha), and adds further complexity to the field development. The Jurassic carbonates (limestones and dolomites) and evaporites are highly heterogeneous both laterally and vertically, have a variety of pore types and are characterized by low porosity (range 0–22%, average 1.8–3%) and permeability (range 0–119md, average 1–2 md). Fractures appear to play a major role in production based on well performance studies. The MM formation is generally considered as pure with >90% of calcite and trace amount of silts and clays, whereas NJ/SG formation is generally considered as dirty with a high content of insoluble mineral, i.e. quartz, silts and clays, etc. Table 1 shows X-Ray Diffraction analysis on core samples from six wells. Reservoir fluids are critical in nature (both gas condensate and volatile oil) and are not distributed uniformly across the project area.

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

Yan

Nasr‐El‐Din

2011

All Days

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Carboxybetaine visco-elastic surfactants have been applied in acid diversion, matrix acidizing and fracturing treatments, in which high temperatures and low pH are usually involved. Amido-carboxybetaine surfactants are subject to hydrolysis under such conditions due to the existence of a peptide bond (-CO-NH-) in their molecules, leading to alteration of the rheological properties of the acid. The objective of this paper is to study the impact of hydrolysis at high temperatures on the apparent viscosity of carboxybetaine visco-elastic surfactant-based acids, and determine the mechanism of viscosity alterations by molecular dynamics (MD) simulations. Surfactant-acid solutions with different compositions (surfactant concentration varied from 4 to 8 wt%) were incubated at 190°F for 1 to 6 hours. Solutions were then partially spent by CaCO3 until the sample pH was 4.5, and the apparent viscosity was measured using a HT/HP viscometer. To determine the mechanism for viscosity alteration on molecular level, MD simulations were carried out on spent surfactant-acid aqueous systems using the Materials Studio 5.0 Package. It was found that short time hydrolysis at high temperatures (for example, 1 to 2 hours at 190°F) led to a significant increase in surfactant-acid viscosity. However, after long time incubation, phase separation occurred and the acid lost its viscosity. Simulation results showed that the viscosity alteration of amido-carboxybetaine surfactant-acid by hydrolysis at high temperatures may be due to different micellar structures formed by carboxybetaine and fatty acid soap, its hydrolysis product. The optimum molar ratio of amido-carboxybetaine and fatty acid soap was found to be nearly 3:1 from our simulations. Our results indicate that hydrolysis at high temperatures has great impact on surfactant-acid rheological properties. Short time viscosity build-up and effective gel break-down can be achieved if surfactant-acid treatments are carefully designed; otherwise, unexpected viscosity reduction and phase separation may occur, which will affect the outcome of acid treatments.

show abstract

A Novel Stimulation Technique for Horizontal Openhole Wells in Carbonate Reservoirs—A Case Study in Kuwait

Cited by 7 publications

References 11 publications

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

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

Combination of Chemical Diverters and Degradable Fiber Technology Enhances the Success of Stimulation in Complex Carbonate Environments

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

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