English Edition (6 MB pdf) - Saudi Aramco

to 60 ft/hour with the hydraulic orienting tool (HOT)
configuration, allowing for all three wells to be completed
two days ahead of schedule.
KSA UBCTD Project Background
The Ghawar field is by far the largest conventional oil field in
the world, and accounts for more than half of the cumulative
oil production of Saudi Arabia. Beginning in the 1980s, deep
drilling through the Jurassic beneath Ghawar field has proved
up large reserves of gas, sometimes with condensate in the
Permian Khuff limestone and pre-Khuff sandstone. Now Saudi
Aramco is developing Khuff and pre-Khuff gas beneath
Ghawar 5 .
In several areas around the world, including the U.A.E. 6, 7
and North America 2, 8 , it was proved that UBCTD reentries
can provide cost-effective access for infill drilling activity.
Testing this technology in the Khuff limestone reservoir was a
logical step towards further opening up those resources. In the
summer of 2008, the first UBCTD pilot project in the
Kingdom of Saudi Arabia was undertaken to evaluate the
feasibility of reentering old wellbores using UBCTD to reverse
declining gas production.
Vertical Khuff gas producers, completed with 4½”, 5½” or
7” liners, were reentered and sidetracked using CT. A typical
operational sequence for the current UBCTD project includes
running and setting a whipstock and exiting the liner by
milling a window, sidetracking the well and drilling one lateral
across the Khuff formation, performing open hole sidetracks
and drilling up to three more laterals. All operations are
typically performed underbalanced while the well is
producing. As of October 2009, 11 wells (31 laterals) were
successfully drilled, exposing up to 7,000 ft of open hole per
well and averaging 1,511 ft of lateral length.
After a nine well pilot phase was successfully completed
using personnel and best practices from around the world, a
great emphasis was placed on further improving UBCTD
project economics through improved operational efficiency
and the introduction of new underbalanced CT drilling
techniques and services.
As lessons were learned and office engineering personnel
and crews on location became more experienced, the average
number of operating days on location required to drill 500 ft
of open hole fell from 4.2 to below three days, Fig. 1.
New Technology Introduction to UBCTD Project in KSA
Since its first deployment in the Middle East at the end of
March 2009 to October 2009, a 3” RSM tool has been tested
in six consecutive wells drilling 15,551 ft in 15 runs and
successfully performing five open hole sidetracks. The RSM
has contributed to achieving the following major
improvements in drilling the lateral sections:
• Optimization of the biosteering process together with
the introduction of new rib steered technology helped
maximize reservoir exposure, extending lateral reach
Fig. 1. UBCTD project days/500 ft.
Fig. 2. UBCTD project motor performance comparison.
and using advanced inclination control modes to stay
within the 2 ft porosity zones. The longest lateral on the
current UBCTD project was drilled with the RSM tool
never leaving the pay zone.
• Average ROP in the pay zone was increased by 35%,
Fig. 2, when drilling with the RSM tool BHA compared
with a conventional oriented bent motor coil drilling
assembly. The rib steered BHA has also set a daily
footage record of 968 ft/24 hrs for the current UBCTD
project.
As an illustrative example of the advantages that rib steered
technology brings to the UBCTD operations, three case
scenarios were evaluated to assess the weight on bit (WOB)
available/reachable depth:
1. CASE 1 - Planned Well Path – AKO 0.8: Using oriented
bent motor, which requires constant orientation and TF
corrections generating an anticipated DLS of 7°/100 ft.
2. CASE 2 - Planned Well Path - RSM: Using rib steered
technology, which requires a straight well profile with
anticipated DLS of 0-1°/100 ft.
SAUDI ARAMCO JOURNAL OF TECHNOLOGY SUMMER 2010 13