English Edition (6 MB pdf) - Saudi Aramco

Successful Deployment of Multistage
Fracturing Systems in Multilayered Tight Gas
Carbonate Formations in Saudi Arabia
Authors: Hasan H. Al-Jubran, Stuart Wilson and Bryan Johnston
ABSTRACT
Horizontal wellbores have enabled significant increases in
productive zone contact areas. With these increased contact
areas, the expected long-term production increases were not
initially realized with conventional stimulation techniques.
Multistage fracturing systems have resulted in impressive longterm
production improvements, but the deployment of these
assemblies into deep and long reach horizontal wells was
initially problematic. After the original difficulties were
encountered, modifications were made to the well preparation
and assembly running procedures, which resulted in the recent
successful deployment of several multistage fracturing systems
into long reach horizontal wells in the Khuff formation in
Saudi Arabia.
This article will discuss several factors impacting the
deployment of assemblies in these conditions, including:
• Construction of the wellbore.
• Deploying through multiple layers with varying
reservoir pressures.
• Preparation of the wellbore.
• Running in hole techniques and procedures.
With the implementation of these well preparation and
deployment techniques, several multistage fracturing
assemblies have been successfully installed allowing proper
placement of multiple fracturing jobs, which have in turn
resulted in continued production improvements from tight gas
formations.
INTRODUCTION
Completions History
In recent years, horizontal well drilling technologies have
advanced, such that operators are now able to drill
horizontally many thousands of feet into productive zones.
There were high expectations that the resulting increase in
contact area would, on its own, result in production
improvements. In many instances, the expected production
increases from barefoot or pre-drilled liners in horizontal
wellbores was not realized. Damage caused by drilling fluids
was determined to be the root cause of the production
impairment of horizontal wells. The most commonly applied
remedy for wellbore damage has been stimulation treat -
ments in the form of proppant fracturing, acid fracturing or
matrix acidizing.
Initial attempts to improve production of horizontal wells
through conventional (bullhead) stimulation techniques were
disappointing. Stimulation treatments would find the weakest
zones in the horizontal wellbore, such as areas of high
permeability or the heel of the well, where all the treatments
would be directed leaving the rest of the horizontal interval
untreated 1 . Post-stimulation production logging revealed that
the majority of production came from a single segment, the
location of which was inconsistent being either at the heel,
middle or toe of the well. Acid washing also resulted in only
short-term and incremental production increases. It was
deduced that mechanical diversion was required to compartmentalize
long horizontal wellbores to allow for individual
stimulation treatments to each compartment, or stage.
Multistage Stimulation Systems
Multistage stimulation systems (MSSs) and their use in
horizontal well stimulation have been previously described in
detail 2, 3 . Briefly, MSSs were first developed in 2002 using
open hole packers on liners with sliding sleeves between each
set of packers. These systems allowed for fracture stimulation
of individual sections of a wellbore based on reservoir characteristics
and production targets.
The MSS consists of ball-actuated or hydraulicallyactivated
sliding sleeves that are isolated using single or
dual-element hydraulically activated mechanical (hydromechanical)
packers. The ball seats in the ball-actuated sliding
sleeves increase in size incrementally, such that the sleeves can
be actuated in succession from toe to heel in a single,
continuous operation. After well stimulation, the actuation
balls are typically flowed back to the surface. This technique
enables the entire horizontal wellbore to be stimulated and
has resulted in significant production improvements enabling
horizontal wellbores to achieve their full production potential.
Khuff Formation in Saudi Arabia
Saudi Aramco is using MSSs in the Khuff formation in the
Haradh field located in east central Saudi Arabia to achieve
34 SUMMER 2010 SAUDI ARAMCO JOURNAL OF TECHNOLOGY