Abstract

Continuing high prices for oil and gas have increased the opportunity for producers to maximize the value of their assets. Under current market conditions, reservoirs previously considered marginal can yield an acceptable return on investment and are increasingly considered for well completion. Many lower-permeability formations require fracture stimulation during the completion phase to deliver economic rates. In the latter part of 2004, a new stimulation technique was introduced to the industry, providing well operators a method to achieve multiple-zone fracture stimulation while controlling stimulation costs. By the end of 2004, this new process had been evaluated by operators in the USA, Canada, and Australia with very positive results.

This new process offers the opportunity to perforate and stimulate multiple pay zones with a single well intervention, often within 1 day. The technique employs a hydraulic jetting assembly on coiled tubing (CT) to erode perforations, after which the treating fluid is injected through the annulus between CT and casing. At the completion of the fracture stage, a small-volume slurry of high proppant concentration is placed in the wellbore to provide isolation of the just-stimulated zone from subsequent targets. This sequence (perforate, stimulate, isolate) is repeated until all desired zones have been treated. Following the final stimulation stage, the well is cleaned out with CT and turned over to production. If needed, N2 gas can be pumped through the CT to kick-off the return flow.

This paper describes the operational aspects, advantages, and limitations of using this new multistage perforation and fracturing technique with example field applications.

Hydrajet-Assisted Fracturing

A number of options exist for completing vertical and horizontal wells that require fracture stimulation of multiple intervals in cased and cemented wellbores. Common methods of stage fracturing include straddle packer assemblies, both on jointed pipe, and, since 1997, on CT; isolating zones using mechanical, sand, and chemical plugs; and more recently, the use of hydrajet-assisted fracturing (HJF).

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