Hydraulic Fracturing

Hydraulic fracturing is a necessary enabler to exploit oil and gas from moderate and tight reservoirs. Numerous novel technologies and state-of-the-art procedures have been applied recently. These include drilling technologies, completions assemblies, stimulation fluids, fracturing proppant, and pumping sequences. The goal of these approaches is to improve the efficiency of hydraulic fracturing, increase reservoir contact with the wellbore, expedite cleanup, and enhance well productivity.

Among the tools and techniques being used to exploit hydrocarbons efficiently are real-time geomechanics to avoid wellbore instability, multistage openhole or plug-and-perforate (PAP) completions to induce multiple independent fractures, high-strength proppants to overcome fluid damage and sustain conductivity during the depletion stages as stresses rapidly increase, clean fluids to ensure permeability stays high and fractures clean up quickly during production while enabling proppant transport and fracture propagation, and pump-stage pulsing to induce open channels to enhance fracture conductivity further.

The widely used resin-coated proppants that prevent proppant flowback during production but contribute to lower conductivity are being replaced by irregularly shaped proppants with grains that bond to one another, thereby preventing proppant movement while providing high conductivity. Initiating and propagating independent hydraulic fractures is challenging in an openhole completion because fractures tend to cross zonal-isolation boundaries, particularly during acid fracturing.

Swellable-packer assemblies, which are much longer than conventional mechanical packers and can assume the shape of the hole, have addressed this challenge somewhat successfully. Swellable packers compress the rock at a much lower pressure than mechanical packers, thereby eliminating rock cracking and the creation of unintentional fractures.

Completing and stimulating wells with PAP technology has gathered attention because zonal-isolation problems are readily solved and multiple independent fractures are generated easily. The challenge is to know and accurately perforate the sweet spots and drill out the plugs efficiently after the treatment. To stimulate long intervals with high heterogeneity and variations in reservoir properties, fluid additives such as chemical and fiber diverters are being improved continuously to achieve near-equal distribution of acid throughout the stimulated interval.

The challenge of breaking down very tight and high-stress formations without reaching tubing pressure limitations and compromising integrity remains, and several processes—including higher completion grading, the use of chemicals and progressive propellant pretreatments, and enhanced perforation techniques—are being investigated.

Improvement in well-stimulation and hydraulic-fracturing processes is dynamic. The USD-30-billion industry contributes to a giant share of the total world energy market. It is truly a great sign and encouragement to see that the industry has the talents needed to optimize the technology.

Additional Reading

SPE 170743 Minimizing Overflush Volumes at the End of Fracture-Stimulation Stages—An Eagle Ford Case Study by Wadhah Al-Tailji, StrataGen, et al.

OTC 24975 Numerical Analysis on the Interaction Between Two Zipper Frac Wells Using the Continuum Damage Method by Xinpu Shen, Halliburton

SPE 163975 Evolving Khuff Formation Gas-Well Completions in Saudi Arabia: Technology as a Function of Reservoir Characteristics Improves Production by Zillur Rahim, Saudi Aramco, et al.

IPTC 16580 Rock Mechanical Properties of Shale Gas Reservoirs and Their Influences on Hydraulic Fractures by Qinghui Li, China University of Petroleum, Beijing, et al.

Zillur Rahim, SPE, is a senior petroleum engineering consultant with Saudi Aramco’s Gas Reservoir Management Department. He is responsible for hydraulic-fracturing and well-completions technologies in the Saudi Arabian nonassociated-gas reservoirs. An active member of SPE, Rahim has authored more than 90 technical papers and has participated as co-chairperson, session chairperson, technical committee member, discussion leader, and workshop coordinator for various international SPE events. He also serves on the JPT Editorial Committee. Rahim holds a BS degree from the Institut Algérien du Pétrole, Boumerdes, Algeria, and MS and PhD degrees from Texas A&M University, all in petroleum engineering.

Hydraulic Fracturing

Zillur Rahim, SPE, Senior Petroleum Engineering Consultant, Saudi Aramco

01 March 2015

Volume: 67 | Issue: 3