Reelwell Drilling Method – full scale verification

O. M. Vestavik, O. Hole, Reelwell as, Stavanger, Norway

This paper was presented at the SAOGE 2008 in Dammam, Saudi Arabia, November 15-17, 2008. It was selected for presentation following review of information contained in the abstract submitted by the authors.

INTRODUCTION

The idea for the Reelwell Drilling Method was born at Rogaland Research (now IRIS) in Stavanger, Norway. The idea was originally motivated by the challenges to solve hole cleaning and Weight On Bit control for coiled tubing drilling applications. After a feasibility study, the method was refined and found applicable to solve several challenges also for jointed pipe drilling. The patented method has unique features for the following applications:

- Managed Pressure Drilling – The pipe connections can be performed at constant downhole pressure without any surface pressure due to a downhole valve solution.

- Liner Drilling – A liner can optionally be installed in the same run as a new section is being drilled. Also there is an option to expand the liner in the same run.

- Deep Water Drilling – The return fluid is transported back to surface through the drill string and the method enables advanced gradients of the annular well fluid.

- Extended Reach Drilling – Hydraulic downhole thrust force and unique hole cleaning. The developments have been conducted according to the following schedule: 2004: The company Reelwell was founded and acquired the IP rights of the technology. 2005: Feasibility study funded by the Research Council of Norway and Statoil. 2006: Shell joined the project, the critical components were built and tested in the laboratory. 2007: Prototype system tested in full scale at the research rig Ullrigg at IRIS in Stavanger. During this development, the Joint Industry Project has successfully demonstrated the drilling system in full scale. The main goal for the project has been to verify the following:

- Proof of concept and the practical application on conventional drilling rigs. - Capability for hole cleaning and downhole pressure/traction control. - Drill-in liner application and the optional liner expansion.

The following presents the basics of the results from this verification program.

EQUIPMENT ARRANGEMENTS

The Reelwell Drilling Method is based on a patented drilling fluid flow arrangement: - A Dual Drill String, where one conduit is used for pumping fluid into the well, and the

other conduit is used for the return fluid from the well. - A Sliding Piston attached to the drill string downhole, is used to allow for dual gradients

of the annular drilling fluid and to aid the pressure/traction control. - An optional liner can be inserted while drilling and expanded downhole in the same run.

This enables simultaneous drilling and lining, and the mono-diameter well design.

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Adaptation to the drilling rig

The Ullrigg Drilling and Well Centre is a well equipped full scale drilling rig with pumps and mud cleaning system and storage tanks, well control equipment, 5” drill pipe etc. The U1 vertical well used in the verification program has a 13 3/8” surface casing to 354 m MD, and a 12 ¼” open hole section to 1258 m MD. A 300 m long 13 ¾” casing was installed and a 80 m long cement plug was placed in the in the lower part of this casing for the drilling tests. Figure 1 presents a schematic of the two arrangements for the verification program, i.e. Plain Drilling and Liner Drilling. The basic set-up with a top string adapter, the dual drill string, the sliding piston, the dual float and the flow x-over, are the same for both arrangements.

Figure 1. Schematic of the Plain Drilling and Liner Drilling arrangements. The Plain Drilling arrangement is shown on the left side of figure 1. The Sliding Piston is attached to the Dual Drill Pipe some distance above the lower BHA. The Dual Float and Flow X-over is positioned at the top of the lower BHA. The Liner Drilling arrangement is shown on the right side in figure 1. This arrangement also includes the following:

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- A Liner Coupling attached to the Dual Float in the lower BHA. - A Liner Expander, attached to the Sliding Piston. - A Liner attached between the Liner Coupling and the Liner Expander. Figure 2 presents a flow schematic of the surface system. On the left of the figure is shown the mud pump which pumps the drilling fluid into the side entry port of the Top String Adapter and down the annular channel of the drill string. The return fluid from the well comes back through the inner channel of the dual drill string and will pass through a surface choke system before returning to the shaker and mud tanks.

. Figure 2. Flow schematic.

On the top of the BOP is installed a Rotating Control Device (RCD) to allow pressurisation of the well annulus while drilling. The upper well annulus between the Sliding Piston and the RCD is pressurised by means of a pump. The drilling sample consists of a 300 m long 10 ¾” casing assembly, hanging in the wellhead. The lower casing joint has a welded steel plug on the bottom end. The casing contains a 80 m cemented section on the bottom covered by ca 15 m sand. This cement/sand sample is used for the drilling trials and will be removed from the well for inspection after the drilling and lining is completed. A ¼” hydraulic control line installed in the annulus between the 13 3/8” casing and the 10 ¾” casing to enable measurement of the well pressure while drilling, and for the kick trials. The upper end of the ¼” line is connected to a pressure gauge at surface near the wellhead. The

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lower end of the ¼” line is connected to the inside of the 10 ¾” casing through a hole is drilled in the casing about 200 m depth, i.e. 100 m above the bottom steel plug The casing joints in the 10 ¾” drilling sample are welded in the connections to avoid that they unscrew during the trials. The casing is locked for possible rotation at the casing hanger by a special arrangement. The 10 ¾” drilling sample is removed from the well when finished. Figure 3 presents a picture of the modified drilling fluid flow arrangement at Ullrigg. The fluid is pumped into the side entry port of the Top String Adapter through a separate 2” hose from the pump manifold. The return flow from the well comes from the top of the Top String Adapter, through the main mud hose. From the stand-pipe the fluid flows through a 2” hose, via the choke and down to the normal return flow conduit.

Figure 3. The flow arrangements at Ullrigg.

Tools and equipment

The following tools were used for Plain Drilling: The Top String Adapter is positioned at the top of the Dual Drill String. This adapter contains a swivel and has one flow port to allow pumping the drilling fluid down into the well and another flow port for the return flow from the well. The top string adapter is attached to a hose for the side-entry inflow and is attached to the conventional swivel in the travelling block for the return flow. The Dual Drill String is a conventional 5” drill string that is modified with inner pipe inserts in a patented arrangement. The arrangement allows for quick and easy modification of a conventional drill string to a Dual Drill String at site. The Sliding Piston is a tool that is attached to the Dual Drill String downhole. It is arranged to always run inside the casing, and it isolates the well annulus outside the Dual Drill String.

Return flow hose to the return line

Top String Adapter with side entry port

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The Sliding Piston is arranged to allow for bypass flow when required, but allows the pressurization of the well annulus between the Sliding Piston and the BOP/RCD. This arrangement converts the well to a hydraulic cylinder, where the Sliding Piston is the cylinder piston and the dual drill string is the cylinder rod. The Sliding Piston allows the use of different fluid properties below and above the piston. Thus it is possible to have a high density kill mud in the well above the sliding piston, while the fluid in the well below the Sliding Piston is a lower density active circulation fluid. The Dual Float is a patented surface controlled valve positioned at the lower end of the dual drill string. The Dual Float enables simultaneous closure and opening of both channels of the drill string. In the fail safe default position, the valve closes both channels of the dual drill string. The Dual Float enables the downhole isolation of the well and thus pressure-less connections at surface during Managed Pressure Drilling operations. The Data Acquisition and sensor package contains mainly pressure sensors and flow meters. The in-flow meter is mounted at the stand pipe manifold and the return flow meter is mounted at the exit of the return choke. The system contains computer model for diagnosis and control. The Rotating Control Device (RCD) is rented from Weatherford, type Williams model 9000. The tool is a simple and passive RCD with a maximum pressure rating of 500 psi. The Upper Annulus Control consist of a pump set up for a maximum flow of around 400 lpm. The pump is remotely controlled from the drillers cabin. The Return Choke is a Remote Dual Choke rented from Ullrigg. The choke panel positioned next to the driller cabin for easy communication between the driller and the choke operator. Additional tools for Liner Drilling: The Liner Expander is a patented arrangement for liner expansion. The Liner Coupling is a patented arrangement that allows for the coupling of the liner to the drill string with built-in switches for flow and rotation control. The Under-reamer is rented from Smith, type DTU 7200. The under-reamer was mounted directly to a 7 7/8” tri-cone drill bit from Smith. The under-reamer was arranged from Smith to open the hole from 7 7/8” to 9.5”. The Spider is rented from Odfjell. This tool acts as a secondary drill-floor and enables the setting of slips on the drill pipe when running the drill string through the 8 5/8” liner, when the liner hangs in slips at the drill floor. Ullrigg was set-up for rotation with a hexagonal Kelly modified with an inner string. The Top String Adapter was mounted on the top of the Kelly.

RESULTS

Pressure and flow tests

Figure 4 presents the results from the initial pressure tests of the upper annular volume in the well, i.e. the volume enclosed by the following surfaces: - in radial direction between the outside of the drill string, and the inside of the 10 ¾” casing, - in axial direction between the closed annular BOP and the Sliding Piston.

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Figure 4 shows the test sequence where the pressure in the well annulus has been increased stepwise to 50 bar using the Upper Annulus Control pump. The test was performed with continuous circulation through the drill bit. As can be observed from the figure the hook load increases in steps according to the increase in the annular pressure. This demonstrates the hydraulic force transfer capability of the Sliding Piston to the hook load. It also demonstrates the sealing capability, as there was no need to supply fluid to hold the pressure.

Annulus pressure test

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Figure 4. Pressure test of the upper well annulus.

Figure 5 presents a situation where the drill string is first lowered into the hole, and then the drill string is pulled out of the hole. One can observe that the return flow from the well is responding immediately when moving the drill string in and out of the well: - When not moving the drill string, the return flow and the inflow both have equal value. - When moving the drill string into/out of the well, the return flow respectively

increases/decreases due to the added closed end steel volume that is lowered into the well.

The figure shows that the differential flow can be measured precisely, and that the sensitivity to detect kick and loss of drilling fluid is high. The resolution in measuring the volume changes by the differential flow arrangement is judged to less than ca 10 liter/min, i.e. very precise and fast compared to conventional detection methods.

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Sand cleaning

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Figure 5. Flow characteristics when moving the drill string inside the well.

Drilling trials

Figure 6 presents the recordings when drilling the cement plug with the plain drilling system. The recordings are performed during the drilling of one drill pipe joint. The pipe joint is drilled down in ca 40 minutes with ROP up to 20 m/h. It is observed that the return flow rate is generally slightly higher than the inflow rate during drilling. The spikes in the return flow measurement at start-up, and occasionally in the following minutes due to pipe movements.

Drilling cement

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Figure 6. Drilling the cement with the Plain Drilling system.

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Cuttings transport. Figure 7 shows the normal cuttings size observed. The cuttings are particles with a maximum size of some few millimeters. However, in some instances particles of 1-3 cm size was produced and efficiently transported to the surface during the drilling operations.

Figure 7. Drill cutting and particle sizes. The demonstration program verified efficient transport of solids up to 10% concentration by volume. No plugging of the return flow conduit occurred during the tests. This demonstrates very high cleaning efficiency, and indicates the potential of the method to solve hole cleaning problems experienced in the field. The surface choke showed once tendency to accumulate cuttings, however, it was successfully cleaned by flushing. Downhole pressure control. The system used for control of the pressure in the upper annulus of the well above the Sliding Piston proved to operate efficiently and reliably. When drilling, the downhole pressure is determined by the drilling fluid density and of the dynamic friction component in the return flow. When the pump is stopped the dynamic component is zero. In order to keep constant downhole pressure in the well during stopping the mud pump, the pressure regulation is achieved by choking the return flow. After the Dual Float is closed, the pressure in the well is isolated downhole by the Sliding Piston and the Dual Float. Thus, during connections there is no surface pressure. When restarting circulation after the connection, the Dual Float is again opened, and the circulation flow rate is established and adjusted so that all required choking is performed through the return conduit and little or no choking is performed on surface. The capability to keep the downhole pressure approximately constant during connections was successfully proven during the test program.

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Controlling influx and loss. The capability for proper well control was demonstrated by:

1. Precisely measure the gain/loss form the well. 2. Control gain/loss rapidly by choke or flow rate control. 3. Close the Dual Float and isolate the well at depth.

The flow sensor arrangement enabled fast and precise detection of kick and loss, and both of the above methods for control were successfully demonstrated. The ability to avoid loss of the annular well fluid above the Sliding Piston was demonstrated in the pressure tests, see figure 4 above. The establishment of detailed well control procedures and the certification of tools are ongoing. Dual Drill Pipe handling. Figure 8 presents situations while handling the DDP during the operations. The figure shows the situation during connection at the drill floor. In general the DDP handling was performed without any large difficulty or problems. Prior to the operations, the insert pipes were individually adapted and inserted into the conventional 5” drillpipe at Ullrigg. The handling of the Dual Drill Pipe then followed similar procedure as conventional pipe handling. The DDP was handled efficiently in singles, and was also racked in stands into the derrick.

Figure 8. Dual Drill Pipe connection.

Liner drilling. The drilling with liner was difficult because of a failure in the rented under-reamer tool. The only available tool suited for our application, had been used for drilling elsewhere prior to the test. The failure implied that the under-reamer arms did not open the hole to the required size. It was decided to stop when the liner was drilled about 20 m into the new section. The liner was then expanded to hang in the 10 ¾” casing and released from the drilling BHA. After liner release, the drill string was pulled to the surface, leaving the 85 m long liner section downhole as planned.

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Tool performance

The Top String Adapter worked without any problems throughout the test period. The Sliding Piston showed excellent performance. The results indicate that ca 30 bar of backpressure gives about extra 10 tons on the hook. The hook load increase represents a hydraulic force provided by the Sliding Piston. This hydraulic force can be converted into a downhole thrust force. The large potential and capacity for hydraulic WOB is thus proven in the program. The Dual Float has been subjected to an extensive test program in the laboratory. The tool experienced a leakage during the first part of the tests, due to a failure in the opening procedure. However, the tool was repaired and performed according to specifications during the rest of the trials. The tool has proven to be efficient for downhole pressure control The Liner Expander has proven to perform well in several tests and the combination of the Liner Expander and the Sliding Piston proved to be a very efficient liner expansion system The Liner Coupling showed good performance during the trials. After pulling out of hole the Liner Coupling was in good condition, and the mechanism for liner release was proven.

CONCLUSION AND OUTLOOK

The Reelwell Drilling Method was successfully proven during the verification program: i.e.: - Sliding Piston provides hydraulic WOB and prevents loss of the annular well fluid. - Efficient hole cleaning and ability to transport large pieces of cuttings in the returns. - Rapid detection of gain/loss volumes less than 100 l. - Downhole well isolation and small pressure fluctuations during pipe connections. - Drilling with liner, including liner hanger expansion and release from the liner after drilling. All components of the drilling system have proven acceptable performance. The verification program was challenged by a hole diameter less than planned, due to a not properly working under-reamer. This issue is expected to be solved in future applications. The program has verified the practical application of the Reelwell Drilling Method. The method has large potential for Managed Pressure Drilling, for challenging pressure zones and depleted reservoirs. The method has special features for extended reach drilling and for deep waters. The next step is to certify the method for offshore drilling in an onshore well.

ACKNOWLEDGEMENTS

Thanks to the Research Council of Norway, Shell and StatoilHydro for their support and funding of the development and test program. Special thanks to Stuart Brown and Bernt Pedersen and their colleagues in Shell, and to Scott Kerr, Alastair Buchanan, Tore Welzin, Arne Torsvoll, Jafar Abdollahi and their colleagues in StatoilHydro for valuable input during the planning and execution of the verification program. Also thanks to Per Simensen and his colleagues at IRIS for their constructive co-operation, and to other co-operating companies and colleagues for their efforts in achieving the successful results.