POLARIS Case Study - France
In 2014, AnTech completed an Underbalanced Coiled Tubing Drilling (UBCTD) project for Lundin Petroleum, operating in the Villerperdue oilfield within the Paris basin, France.
Objectives & Challenges
The field was mature and the wells were depleted to a point where they need to be pumped to produce. The main objective of the operation was to increase the production by drilling a new lateral from an existing wellbore to access a new area of the reservoir.
Furthermore the project required the team to initiate an open-hole side-track inside the porous reservoir boundaries without dropping more than 2m from the existing wellbore, either during the open-hole side-track or the target 300m lateral, while keeping the well underbalanced. The proposed well was already horizontal with the casing shoe set at just below 70° from vertical. The reservoir section had previously been drilled with a 6-1/8” bit and completed open-hole.
Villerperdue, Paris Basin
Onshore - Oil
For any Coiled Tubing Drilling (CTD) job to be viable, it is fundamental that the coiled tubing is capable of transferring sufficient weight to the bit in order to maintain an effective rate of penetration. In addition, while maintaining a sufficiently energetic flow regime in the annulus to clean the hole, the downhole pressures must be low enough to prevent lost circulation and formation damage and the internal coiled tubing pressure at surface must be low enough to avoid premature tubing fatigue.
In order to ensure that these conditions could be met during the Villerperdue operation and that the work could be completed successfully, considerable pre-well analysis and modelling was carried out. The modelling was completed in-house by AnTech using its proprietary software, which was designed specifically for CTD operations modelling. Feasibility modelling focussed on three main areas: well path planning, tubing forces and hydraulic modelling.
Tubing forces modelling indicated that achieving sufficient weight-on-bit (WOB) should not be a problem, with just over 15kN WOB achievable in the reservoir zone. Hydraulic models were run to show the expected pressure at any point within the well and enabled AnTech to determine which of its two BHAs would be suitable for the operation.
AnTech compared achievable Bottom Hole Circulation Pressures (BHCP) at a variety of liquid and gas phase flow rates using the 3.192” outside diameter (OD) COLT and 5” OD POLARIS™ BHAs. Hydraulic modelling clearly demonstrated that it wouldn’t be possible to clean the well of cuttings within the motor flow limits for the smaller COLT tool. However, modelling revealed it would be possible to clean the well and maintain the desired underbalanced conditions at a range of different fluid and gas phase flow rates with the larger POLARIS tool.
The drilling fluid selected for the operation was a combination of nitrogen and diesel. This fluid mix was selected due to the reactivity of the surrounding formation whilst maintaining underbalanced conditions.
Figure 1 - Plan view showing the existing well and actual path drilled
Results & Benefits
First 5” Coiled Tubing Drilling BHA deployed in Europe.
1,437ft (438m) lateral was drilled in the target formation.
Achieved an open hole side-track inside the porous reservoir boundaries - 4m thick.
- 100% clean health and safety record.
- Captured technical learnings and best practices.
Complete Directional Coiled Tubing Drilling Package.
Bespoke well path planning and feasibility modelling.
A range of Bottom Hole Assembly sizes suitable for re-entry and grass-root applications.
Reduced operating costs as both drilling time and rig-up time are quicker with CTD.
Underbalanced drilling protects the formation and allows production to continue whilst drilling.
Figure 2 - The AnTech Mobile Workshop
Figure 3 - Picking up POLARIS
Onshore - Oil
As a result of the pre-well modelling, the POLARIS BHA was selected for the operation, making it the first CTD BHA of its size to be deployed in Europe.
The magnetically-steered tool configuration developed by AnTech specifically for this project enabled uninterrupted fluid circulation, thus avoiding downtime that would otherwise be required to allow stable flow conditions to be re-established after stopping and then re-commencing circulation. Owing to the fact that it typically takes a long time to re-gain equilibrium with multi-phase flow, this reduction in downtime offers significant time and cost savings. Magnetic measurement also eliminated the need to stop pumping in order to take a survey (which would be required by a gyro steered or drill pipe conveyed tool), therefore providing constant directional survey data. This real-time feedback provided the high level of accuracy required to reduce the risk of dropping below the narrow target formation when performing the open-hole side-track in the already horizontal wellbore. The results demonstrate that AnTech’s POLARIS tool is suitable for drilling directionally, whilst maintaining sufficient two-phase flow for effective hole cleaning.
The project was completed in collaboration with two other partners to provide the complete service package for the operator. AnTech successfully drilled, to target, a 438m lateral within the required window at speeds up to five times the rate at which the original lateral was drilled in overbalanced conditions. The well was kept fully contained at all times and there were no HSE incidents during any stage of the operation.
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