English Edition (6 MB pdf) - Saudi Aramco

Next Generation Technologies for
Underbalanced Coiled Tubing Drilling
Authors: Shaker A. Al-Khamees, Anton V. Kozlov, Serve Frantzen, Thomas Gorges, Julio C. Guzman Munoz, Anthony A. Aduba
and Thiago P. da Silva
ABSTRACT
Technology improvements are continuing to expand the
capability of coiled tubing directional drilling (CTDD)
worldwide. Increased CTDD activity in advanced under -
balanced reentry applications that require precise wellbore
(multilateral) placement and real-time monitoring of
downhole parameters has led to the development of bottomhole
assemblies (BHAs) with enhanced functionality.
Saudi Aramco identified CTDD as an important technology
for redeveloping its gas reserves and is dedicated to expanding
the technical limits of the CTDD application. Saudi Aramco
successfully completed its first underbalanced reentry coiled
tubing drilling (UBCTD) pilot project and is now progressing to
consolidate this technology in subsequent UBCTD operations.
A great emphasis has now been placed on further improving
UBCTD project economics through improved operational
efficiency and the introduction of new underbalanced coiled
tubing (CT) drilling techniques and services.
This article provides an overview of the new rib steered
motor (RSM) technology and its potential benefits to UBCTD.
It details recent worldwide deployments of the rib steering
motor technology, focusing on operations in the Kingdom of
Saudi Arabia, which provide the perfect testing ground when
geosteering with RSMs. Future advances using UBCTD
geosteering technology rely on a close working relationship
between the field operator and the service company. Successful
application of UBCTD to a wide range of mature oil and gas
fields will enhance access to the producing reservoir and drive
the economic extraction of additional reserves.
INTRODUCTION
Even with the use of cutting-edge technology and knowledge
application in coiled tubing directional drilling (CTDD), there
are limitations to drilling with coiled tubing (CT), of which
the most significant are the inability to drill a straight well
profile and transferring adequate weight to the bit 1 .
Through the process of miniaturization and innovation, a
small diameter rib steered directional drilling system has been
developed for underbalanced reentry coiled tubing drilling
(UBCTD). The introduction of the rib steered motor (RSM) is
aimed at overcoming inherent wellbore tortuosity characteristics
created while using conventional oriented CTDD bottom-hole
assemblies (BHAs). Furthermore, the RSM’s enhanced
geosteering capabilities and reduced dogleg severity (DLS) serve
to extend the lateral reach potential before CT lock-up.
Rib-steering technology has been successfully tested on the
North Slope of Alaska, in North Texas 2 and most recently on
the UBCTD project in the Kingdom of Saudi Arabia (KSA).
Straighter, longer horizontal laterals, and improved steering in
borehole sizes as small as 2¾”diameter have been achieved,
consequently improving the precision of well placement when
geosteering within the narrowest of pay zones.
TECHNICAL BACKGROUND
CT material properties are such that only a small percentage
of the drillstring weight actually gets transferred to the bit.
Unlike conventional drilling where the drillpipe weight is
regulated via the rig brake, CTDD requires a mechanical
injector at the surface to push the coil in the hole to get
adequate weight transfer to drill. Because of the mechanical
properties of CT, as the compressive forces are increased,
the coil buckles in a sinusoidal fashion. When the com -
pressive forces are further increased to a critical level, the
tubing deforms into a helical shape. Any additional force
applied will increase the normal force of the CT against the
wall of the well. The transferred weight to the wall of the
hole, along with the wall friction, opposes the movement of
the CT in the hole – a condition known as helical lock-up 3 .
While the industry continues to explore options to improve
the properties of the CT itself; if the friction losses
encountered while drilling could be reduced, the weight
would be more efficiently transferred to the bit. This
limitation in CT drilling indicated the need for development
of other techniques.
Good hole cleaning procedures have been developed over
the years to reduce friction losses. Along with improved fluids
and wiper trip schedules, the option to continuously circulate
even while tripping resulted in eventually overcoming part of
the weight transfer issue. The development of tools for
underbalanced drilling and managed pressure drilling
techniques, along with the expertise gained with experience,
have led to an improvement in the lateral lengths that can be
drilled today.
SAUDI ARAMCO JOURNAL OF TECHNOLOGY SUMMER 2010 11