Technology Updatae: New Methods Boost Multistage Fracturing in Horizontals
Authors: JPT staff _ 
Published: February 2015

In horizontally completed wells, as in those that are vertically completed, underachieving wells are commonplace. There are many potential causes; however, this problem often can be attributed to one or more of the following circumstances:Permeability anisotropy, tending to limit vertical permeability especiallySkin damage or near-wellbore plugging of a natural fracture networkIneffective stimulation techniques
Fracturing technology for horizontal wellbores continues to evolve. The technique of using the dynamic movement of fluid to divert fluid flow into a specific point in the formation has proved effective in creating and accurately placing fractures in openhole horizontal wellbores. A need for equally effective advanced stimulation technology has existed for cased horizontal wellbores. Two new developments by Halliburton, extending the scope of completion and fracturing technologies, are enabling operators to fracture cased horizontal wellbores more effectively: sliding-sleeve completions and coiled-tubing (CT) fracturing applications.

Sliding-Sleeve Completions
The use of sliding sleeves for horizontal cased-hole fracturing is being adopted rapidly by the industry. This method (Fig. 1) provides operators with another well-architecture option for completing multizone wellbores effectively and economically with minimal or no intervention. The technique uses two newly developed tools—a stimulation sleeve and a swellable packer—to enable selective access to multiple pay zones in a single wellbore, with the option of closing or opening one or more zones at a later date.
Designed to be run as part of the casing string, the stimulation sleeve enables the performance of selective multizone operations through the production string. The sleeve can be operated by using a mechanical/hydraulic shifting tool run on coiled or jointed tubing, or by using a ball-drop system. Opening the sleeve permits zonal stimulation through the selected sleeve and diverts the flow through the ports in the sleeve. After stimulation, cleanup is aided by flowing all lower zones simultaneously. Once cleanup is finished, the sleeve functions as a standard production device, allowing full wellbore access.
The swellable-packer isolation system is a zonal-isolation device based on the swelling properties of rubber in the presence of hydrocarbons and requires no mechanical movement or manipulation to set. It can swell to as much as 200% of its original size to seal the annulus around the pipe, isolating the producing zones. Swelling time can be controlled for each specific application.

East Texas Case History
An east Texas operator needed to stimulate five naturally fractured intervals in a multizone horizontal wellbore. Normal cementing-completion methods were not an option because they would restrict production. The operator chose the sliding-sleeve completion process, which included a liner hanger to isolate the formation from the upper wellbore and provide a means to tie back to the surface. The process also included a swellable-packer system to isolate the annular area between zones. Liquid hydrocarbons were introduced into the annulus to swell the packers. The sleeves were opened selectively by dropping balls from the surface. Five zones were stimulated successfully in 20 hours with 1.3 million lbm of proppant and 2.1 million gal of gel in continuous pumping.