English Edition (6 MB pdf) - Saudi Aramco

Merging Tapered-in Coiled Tubing (CT) and Well
Tractor Technologies to Effectively Stimulate
Extended Reach Open Hole Horizontal Wells
Authors: Mubarak Al-Dhufairi, Saleh A. Al-Ghamdi, Vidal Noya, Khaled Al-Aradi, Samer Al-Sarakbi, Ahmed Al-Dossary,
Ernie Krueger and Dr. Norman B. Moore
ABSTRACT
The Manifa field development involves one of the largest
drilling projects in Saudi Arabia, targeting various carbonate
reservoirs, with an extraordinary amount of extended reach
wells (ERWs) required to meet the expected oil production
rate, at the lowest development cost possible. More than twothirds
of the wells fall under the extended reach drilling
classification, and the majority of the wells have measured
depths (MDs) between 24,000 ft and 31,000 ft. These wells
are open hole completions where acid stimulation is greatly
needed to overcome reservoir damage and improve the wells’
performance after drilling operations terminate.
The placement of the treatment fluids requires a uniform
distribution along the open hole section. Among the different
techniques considered, namely bullheading, using the rig drillpipe
and coiled tubing (CT), the last one offered the soundest technical
and cost option. However, the CT technique alone did not show
the ability in reaching the maximum depth in most ERWs of this
field. Therefore, the tractor 1 was required to provide the significant
amount of pull force needed to operate inside these long distances,
something not seen before in open hole completions.
The first eight well campaigns, using a combination of CT,
a hydraulic tractor and friction reducer fluids, achieved the
main objectives. Moreover, a new intervention world record 2
was set when the CT bottom-hole assembly (BHA) reached
the maximum depth of 28,257 ft inside the open hole on two
different occasions, to place the stimulation fluids, and to
record an injection profile. During the campaign, a total of
41,774 accumulated footage was operated with the tractor,
allowing over 3,400 bbls of acid to be placed in direct contact
with the formation. As a result, the average injection rate
increased more than tenfold, reducing the drilling
requirements for injection wells originally projected.
The job preparation, technology, results, learning curve
experience and best practices are discussed in this article,
including proposed operational enhancements. This experience
demonstrates the feasibility of the operations with CT
required for full zone coverage, yielding optimum water
injection rates at the lowest development cost.
INTRODUCTION
One of the largest worldwide oil field developments currently
ongoing, the Manifa field is a giant offshore field that covers
more than 800 square kilometers (km 2 ). Located in the northeast
part of Saudi Arabia, the field lies under shallow waters. The
main drivers behind the Manifa field development plan called for
meeting the production targets at the lowest development and
operating cost, and in a safe and environmentally friendly
manner. To achieve this, a decision was made to utilize a 21 km
long causeway in combination with extended reach wells (ERWs)
to reduce the need for offshore platforms 3 from 30 to 11. More
than two-thirds of the wells were considered extended reach
drilling by industry standards, reaching depths up to 31,000 ft.
To maximize the oil recovery, water injection secondary
recovery was planned for efficient sweeping of hydrocarbons
in the reservoir. Most of the wells are water injectors drilled
from the coast of the mainland. Oil producing and water
injection wells are completed as open hole with a 6 1 ⁄8”
diameter, Fig. 1. In spite of the best drilling practices utilized,
acid stimulation was required to remove any formation
damage created in the open hole section of the well.
The treatment should strive to improve the injection/
production rates in a uniform pattern by eliminating or
bypassing the damage. Several methods were considered to
perform the stimulation treatment, including use of drillpipe,
bullheading and coiled tubing (CT) equipment to convey the
fluids. The drillpipe option is expensive and has not delivered
good results, while bullheading experiences have not been
effective in ensuring a uniform distribution of fluids. Using CT
offered the best chance for uniform coverage of the open hole
section at the lowest cost.
The extreme length of the ERWs of the Manifa field
presented the risk of not being able to reach the maximum
depth of the open hole section with the CT string. Traditional
techniques for assisting CT to reach total depth (TD) included
the friction reducer fluids, pipe straightener, downhole
vibration tools and hydraulic actuated tractors. Simulations of
tubing forces in the CT with specialized software indicated
that loads up to 8,000 lbs at the bottom-hole assembly (BHA)
were necessary to pull the CT and reach TD in most ERWs.
Based on this analysis, downhole hydraulic actuated tractors
were perceived as the only viable alternative to enable the
intervention with CT.
Experiences with CT tractors in open hole environments
was minimal at the time the Manifa field development started,
with no case study similar to the expected conditions, making
2 SUMMER 2010 SAUDI ARAMCO JOURNAL OF TECHNOLOGY