Offshore Hydraulic Fracturing Technique
Authors: Meese C.A. , Mullen M.E. , Barree R.D. 
Published: December 2007

Technology Today Series

This paper describes the "frac-and-pack" completion technique currently being used in the Gulf of Mexico, and elsewhere, for stimulation and sand control. The paper describes process applications and concerns that arise during implementation of the technique and discusses the completion procedure, treatment design, and execution.

Introduction

An innovative well-completion technique, frac and pack, recently has been introduced into Gulf of Mexico well-completion operations. The technique combines the stimulation advantages of hydraulic fracturing with the sand-control technique of gravel packing. The method involves a one-step fracturing and gravel-packing operation performed through conventional downhole gravel-packing hardware.

The technique is being used successfully to reduce skin damage effects and to improve the productivity of unconsolidated sandstone completions significantly by creating better communication between the wellbore and the reservoir. An example of the productivity improvement related to frac and pack is provided in the Conclusions and References. Successful fracturing of soft formations poses challenges different from fracturing of typical hard rock. The primary difference is the use of tip-screenout designs and very high sand concentrations to ensure adequate fracture conductivity between the reservoir and the wellbore. Many authors have described tip-screenout fracturing techniques.

Although new to the U.S. gulf coast area, hundreds of these treatments have been per formed during the last 2 years. Job sizes ranging from 10,000 to 200,000 lbm of proppant have been pumped successfully from stimulation vessels in the Gulf of Mex ico. Stimulation service companies are gearing up for an increase in demand for this service. The stimulation vessels are equipped with pumping output ratings to 4,000 hydraulic hp, pressure ratings to 15,000 psi, fluid-handling capabilities to 3,000 bbl, above-deck proppant-handling capabilities to more than 200,000 lbm, and blending capabilities to 30 bbl/min at more than 10,000 lbm/min.

Applications and Concerns

Many reasons exist for applying hydraulic fracturing techniques to friable or unconsolidated sandstone reservoirs. A propped hydraulic fracture can accelerate production from lower-permeability wells and increase recoverable reserves economically. Induced propped fractures also can be used to bypass deep formation damage or to increase vertical flow conformance in higher-permeability applications or laminated reservoirs.

The following conditions are candidates for Gulf of Mexico frac-and-pack applications.Reservoirs with significant wellbore damage that historically respond poorly to matrix stimulation techniques. An induced hydraulic fracture can bypass damage and connect the wellbore to the reservoir efficiently, there by reducing skin effects.Poorly consolidated reservoirs that may have fines and sand migration problems. An induced hydraulic fracture can alleviate fines movement by providing a larger high-permeability flow area, which will reduce near-wellbore fluid velocities. Reduced fines migration leads to better cumulative production.Low-resistivity, laminated sand/shale sequences where the connection of the sand lenses to the wellbore through perforations may be limited. An induced hydraulic fracture can provide an effective vertical connection. Sands once thought to be uneconomical in the offshore environment are now becoming attractive because of this new completion method.Low-permeability reservoirs that require a conductive fracture to improve the overall productivity of the zone.

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