Case History: How to Enable the Horizontal Development of Shallow Reservoirs

This summary is based on the paper "How to Enable the Horizontal Development of Shallow Reservoirs," presented by Wolfgang Mathis, Harald Strand (NeoDrill AS), and Gerald Hollinger (OMV Norge AS) at the SPE/IADC Drilling Conference and Exhibition, 2017. The full paper can be accessed through the Society of Petroleum Engineers.

Essential Highlights

• CAN Technology Overview:

  • The Conductor Anchor Node (CAN) is a suction anchor-based well foundation designed to support the conductor, BOP, and wellbore loads. It integrates a guide pipe to ensure vertical installation and provides a stable foundation for shallow reservoir development.

  • The technology reduces rig time by allowing pre-installation of the CAN and conductor before the rig arrives.

• Wisting Central II Case Study:

  • OMV (Norge) AS successfully drilled a 1.4 km horizontal section into a shallow reservoir (250 m below mudline) in the Wisting field. The CAN-ductor design, which features a shorter conductor (11 m), was essential for achieving the shallowest horizontal well ever drilled from a floating unit.

  • The CAN allowed for significant vertical depth (TVD) for building the hole angle, enabling the successful penetration of the shallow reservoir.

• Operational and Cost Benefits:

  • Installation by vessel, rather than rig, reduces costs, saves rig time, and enhances safety. The CAN eliminates the need for heavy cement jobs, large conductor handling, and guide bases.

  • Average conductor setting time was reduced from 3 days to 1.2 rig days due to the CAN system.

• Geotechnical Considerations:

  • Soil conditions at the Wisting location required careful assessment to ensure the CAN's load capacity and stability. The geotechnical assessment included evaluating shear strength and soil conditions.

• Successful Results:

  • All well objectives were met, with the CAN providing stability and load-bearing capacity, leading to a simplified well architecture and lower costs.

  • The project demonstrated the potential for CAN technology to reduce environmental impact and improve operational efficiency in shallow reservoirs.

  
  

Abstract

The Wisting Central II well, located in the Barents Sea, faced the challenge of drilling into a shallow reservoir just 200-250 meters below the mudline, making it difficult to build the necessary well angle for horizontal entry. To overcome this, OMV (Norge) AS utilized NeoDrill’s CAN-ductor system, which integrates a short conductor (only 11 meters) into a suction anchor foundation (the CAN), providing the required load capacity. This innovative approach allowed for the successful drilling of a 1.4 km horizontal well at 250 meters TVD below the mudline, making it the shallowest horizontal well ever drilled from a floating unit. In addition to the technical success, the CAN-ductor system also resulted in significant cost savings by reducing rig time, eliminating the need for remedial cementing, and simplifying plug-and-abandonment (P&A) operations.

Introduction

The CAN well foundation, developed to improve top hole well construction, functions as a suction anchor with a guide pipe, allowing pre-installation by vessel to save rig time and ensure conductor stability. Initially deployed by Eni Norway in 2006 for deepwater wells, the CAN demonstrated unmatched efficiency, significantly reducing conductor installation time and mitigating risks related to well integrity. Since then, the CAN has evolved with 15 installations in depths of 125 to 1444 meters, proving to be a cost-effective solution for soft seabeds and conductor fatigue. A key application was Statoil’s Peon field, where the CAN provided a perfect soil-to-conductor seal, ensuring well integrity. The Wisting Central II well represents the latest example of the CAN’s potential in shallow reservoirs.

CAN Design

For successful CAN deployment, location-specific geotechnical data is required to determine penetration and load-bearing capacity. Since the Wisting well was an appraisal project, the CAN foundation was rented. CAN units of 6 meters in diameter, with heights between 7.5 and 11 meters, were available for use.

Conductor Integration

The conductor was integrated into the CAN at the workshop before shipment, following a series of welding and cementing steps. The conductor anchor was welded to the guide pipe, ensuring a total axial load capacity of 1050 tons, with cement filling the annulus for added stability. This method minimizes fatigue risks by avoiding hot work near the wellhead and uses standard components for quick assembly. Though slightly heavier than a standard CAN, the 93.5-ton structure was easily managed during installation.

Guide Post Receptacles

The CAN also includes integrated guide post receptacles, eliminating the need for a separate guide base. This feature further reduces costs and simplifies rig operations during the installation process.

Geotechnical Assessment

Before installing the CAN, a geotechnical analysis of the seabed was performed to determine the required CAN dimensions and load-bearing capacity. CPT data from nearby locations showed variability in soil strength, with favorable conditions at CPT 10 but stronger formations at CPT 03, which could limit penetration.

A geotechnical correlation confirmed that a consolidated layer at 27 meters would not affect CAN installation at the planned depth of 7.5 to 11 meters.

CAN Dimensions and Load Capacity

Among the available CAN units (6 meters in diameter), the 11-meter CAN was selected due to its load capacity, which exceeded design requirements by more than double, providing a safety factor greater than 2.

Backup Scenarios

In case of unexpected increases in soil strength, two additional scenarios were analyzed. Even with early refusal at 6.6 meters, the CAN maintained sufficient capacity with a safety factor of 2.22, ensuring it would meet load requirements.

CAN Installation

The CAN was installed at the well location in December 2014, but the ROV survey revealed a significantly sloping seabed, causing a 3.3° tilt in the CAN. To correct this, the CAN was partially lifted, and the installation vessel was repositioned to reduce the tilt. After adjustments, the final inclination was brought to 0.18°, well within the acceptable limit of 1.0°.

The CAN achieved full penetration of 11 meters, with a slope of 0.9 meters across its diameter, equivalent to an 8.53% seabed slope. The final installed position was within target range, with a slight deviation in orientation to 171.30° (from the target of 180°).

Geotechnical Back-Calculation

After the CAN installation, recorded data was used to update the geotechnical model and verify the actual load capacity of the CAN. This is a unique advantage of the CAN system, allowing precise verification of load capacity. The back-calculation matched the measured underpressure to soil parameters at the site, adjusting for initial data uncertainties due to CPT tests from distant locations. Deviations in the data were attributed to setup delays and the sloping seabed. The final load capacity was higher than predicted due to increased resistance from the CAN lid coming into contact with the seabed at 10 meters depth.

Drilling Phase

The Wisting Central II well successfully demonstrated horizontal drilling in a shallow reservoir, achieving a 2.5° inclination at 50 meters and completing a 1.4 km horizontal section. The CAN installation confirmed that shallow-set conductors (10 meters) are sufficient, with no borehole instability.

The CAN's verified inclination (0.18°) before rig arrival saved rig time, and no movement was detected during the 70 BOP days. Installing the conductor by vessel reduced handling, HSE risks, and eliminated the need for a cement job or guide base. The simplified casing cutting process and flexible installation schedule further minimized risks and costs.

Results and Conclusions

The Wisting Central II well achieved all its objectives, becoming the shallowest horizontal well drilled from a floating unit. A key factor was the integration of the conductor into the CAN foundation, reducing the conductor from four joints to one and providing the necessary TVD for the high dog leg trajectory. Despite the lack of CPT data at the spud location, the CAN performed as expected, delivering the required load capacity.

Cost Savings

The CAN system contributed to significant cost savings, reducing rig time by 1.2 days, or 40%. Savings came from avoiding extra conductor joints, running tools, BHA, cement jobs, and guide bases. The system also reduced P&A time and non-productive time risks.

Further Developments

There is potential for further optimization by reducing casing sizes, which would lower construction costs and enable greater dogleg angles. The CAN supports the conductor, significantly reducing bending moments, and allows for integrating the kick-off point, giving better control over well deviation.

Acknowledgements

The authors would like to thank OMV (Norge) AS for allowing to publish the information presented in this paper.

For more detailed insights, the full paper can be accessed through the Society of Petroleum Engineers.

References: Mathis, W., Strand, H., & Hollinger, G. (2017). Case History: How to Enable the Horizontal Development of Shallow Reservoirs. Presented at the SPE/IADC Drilling Conference and Exhibition, The Hague, Netherlands, 14-16 March. SPE-184667-MS. Retrieved from Society of Petroleum Engineers.