COLT Case Study - Alaska
The UBCTD project that boasts the longest CT Drilled lateral and the first ever triple casing exit on wireline.
Directional Coiled Tubing Drilling (DCTD) and RockSense were utilised in an oilfield on the North Slope of Alaska. AnTech’s Continuous Rotating Orienter (CRO) made it possible to drill one of the longest laterals in the world with CT. In addition, the CRO enabled a record ROP and the longest liner run in a single trip with CT. Real-time gamma measurements were used alongside RockSense to geosteer the well.
Objectives & Challenges
The two wells under consideration in this case study were oil producers. The laterals, running in a sand formation, were planned with the primary objective to access heavy oil reserves which cannot be economically accessed with conventional drilling. CTD was seen as the best way to drill the reservoir because of cost advantages as well as the ability to drill using managed pressure, at-balance, with the reservoir at a stable bottom hole pressure.
USA - Alaska
Onshore - Oil
For the project to be economically viable, it was determined that laterals up to 6,246 ft were required. This length could not be achieved with a 7 deg /100 ft wavy well path adopted in previous projects and derived from the orienter technology being used. AnTech addressed the issue by deploying its own CRO which has the ability to drill a perfectly straight hole as well as the curve in one run. It is possible to steer using build rates that are between the maximum build given by the motor bend and straight tangent sections. This gives a very flexible steering capability.
In the early stages of the project, it was decided to take advantage of RockSense, AnTech’s proprietary real-time, at-bit, synthetic porosity signature software for bed boundary identification (fig. 1). This technology offers two considerable advantages over traditional geosteering techniques. First, operators can gain inch-level resolution because multiple measurements can be made for every foot drilled, due to wired telemetry having a high data rate. Second, formation boundaries can be detected at the bit, not 20-30 ft behind the bit, as the software can tell the directional driller whether a bed boundary has been penetrated within inches of the BHA passing through it. Therefore, the driller can deliver an optimally placed wellbore and respond to changes in formation as the bit passes through them. The synthetic porosity measurements from RockSense were coupled with gamma readings to further improve TVD accuracy (fig. 1). RockSense values decrease with increasing porosity and vice versa.
Figure 1 : RockSense associated to the drilled trajectory
Figure 2: CTD Rig
Figure 3: CTD Work Shop
- Triple casing exit
- 7,132 ft lateral
- 2,894 ft in 24 hrs
A triple casing exit was performed as planned for both wells by milling through the 4.5”, 7.0” and 9.625” strings with two trips being required. This was the first triple casing exit performed with CT on the North Slope. After the triple window was milled, AnTech circulated the hole clean prior to POOH with the milling BHA and prior to tripping back in to drill the build section. A drilling BHA was run for the build section.
The build and straight sections of the wells were drilled with the same BHA configuration because of the ability of AnTech’s CRO to continuously rotate and to hold a constant toolface for directional work. The CRO withstands the high vibration and shock loads due to its purpose-built drivetrain. Since the CRO does not need drilling fluid for actuation, the BHA was able to change direction while drilling ahead and all the differential pressure was available to drive the motor. This also avoided the problem of residual torque in the string that could have been released when the bit was taken off bottom. These unique CRO features resulted in one of the longest laterals being drilled with CT in the world, with a record value of 7,132 ft. AnTech also achieved the ROP record of 2,894 ft in 24 hours. It was also the longest single trip casing run utilising CT performed in the world.
It was decided to geosteer the lateral through the West Sak formation while maintaining the proposed azimuth. The depth was correlated against existing cased hole gamma ray plots on every RIH and wiper trip to improve TVD accuracy. AnTech worked hand in hand with the Operator’s wellsite Geologists to ensure the maximum pay formation was accessed by the wellbore. Azimuth control of the wellbores was also imperative, as there were other wells nearby which were designed to parallel and align with these two wells under consideration.
Results & Benefits
Real time information on geological markers available
Real-time data aggregation and real time decision making
First triple casing exit on the North slope
One of the longest laterals drilled with CT in the world
Highest footage drilled using CTD in a 24 hour period on the North Slope
longest casing run in a single trip with CT in the world
Pre-job engineering and Project Management (AIM)
Complete Directional Coiled Tubing Drilling (DCTD) package
Geological marker identification using RockSense and gamma
Conversion kit to convert the rig to e-line
Well planning and feasibility modelling
The Future of Directional CTD Applications
Operators around the world are looking at Directional Coiled Tubing Drilling (DCTD) as a reliable and economically viable technique for unlocking the potential of mature and under-producing oilfields. Both onshore and offshore. It is the safest and best way to drill underbalanced because the well is contained at all times.
DCTD technology and experience have advanced significantly over the past few years and that forms a strong basis for future work.
COLT - ALASKA
3% KCL brine 8.8 ppg
3% KCL brine 8.8 ppg