Frequently Asked Questions for EC-Drill®

EC-Drill^® is a Controlled Mud Level (CML) technology that allows manipulation of bottom hole pressure (BHP) while drilling a well. The system controls the BHP by adjusting the fluid level in the marine drilling riser, and thereby the hydrostatic pressure applied. This is achieved by installation of a Subsea Pump Module (SPM) on the riser which pumps all mud and cuttings returns up a separate Mud Return Line (MRL). The system can be used to adjust bottom hole pressure at any point during well construction regardless of whether or not the drill string is currently in the well. It can be used for many applications, including the traditional MPD application of holding BHP constant when pumps are started and stopped during a connection.

By the IADC (International Association of Drilling Contractors) categorization System, EC-Drill^® is a Controlled Mud Level (CML) system, it controls the mud level in the marine drilling riser. As a marine drilling riser is installed, the system is only applicable to offshore wells.

No, EC-Drill^® manipulates the fluid level in the marine riser and does not require a Rotary Control Device (RCD) or an additional choke manifold at surface contrary to Surface Back Pressure MPD.

Some applications for EC-Drill^® include

• Drilling depleted zones
• Drilling narrow windows
•  Running casing and cementing in depleted zones and narrow windows
•  Running completions in depleted zones and narrow windows
• Drilling into unknown pressure regimes
• Extending shallow casing strings via the dual gradient effect
• Freeing differentially stuck wireline tools, stuck completion assemblies or drillstring
• Drilling zones with risk of high or total losses
• Well Testing operations: reduce level to increase production flow temperatures

EC-Drill^® use is limited to offshore wells. It is normally used on wells drilled from floating rigs (semi-submersible or drillship) using a subsea BOP. EC-Drill^® has also been used on jack up rigs during the initial hole sections taking suction from the conductor. There is also application for use on specific platform applications with a surface BOP when a subsea casing hanger system and separate drilling riser is used.

CMCD is Controlled Mud Cap Drilling. This is a method of addressing total losses on a well using a sacrificial fluid to drill the reservoir and a heavy mud monitored in the annulus. With EC-Drill^®, it is straight forward to use this method to address total losses on a well and has an easy transition to and from “conventional” MPD with EC-Drill^®.

EC-Drill^® does not require a MPD ready rig as it can install on any offshore mobile drilling unit. The surface pipework that is required by EC-Drill^® is minimal. If the rig is “MPD ready” for Surface Back Pressure (SBP) MPD, some of this pipe work can likely be used, but the amount EC-Drill^® surface pipework is small, and this would not be a major factor in installation of EC-Drill^® on a rig.

EC-Drill^® to date has been used offshore Brazil, offshore Mediterranean, in the North Sea, in the Barents Sea and in the Gulf of Mexico. It is applicable from shallow to ultra deep water application, with jack-up, semi-submersible or drillship.

Yes, EC-Drill^® is well suited to manage pressure during cementing operations. The EC-Drill^® system can easily perform Managed Pressure Cementing (MPC) in an operationally convenient manner. The combination can allow for use of more conventional cementing techniques in some cases.

No, the EC-Drill® equipment is run with the drilling riser. It remains subsea and available for use during the entire period of the well drilling operation. It is then recovered with the BOP at the conclusion of the well.

An EC-Drill^® ready rig is in a rig where the supporting equipment is available to allow operation to commence within a short lead time. The only equipment to be mobilized is a Subsea Pump Module and Control system.

Once the EC-Drill^® system has been installed on the rig, our clients typically see additional applications for EC-Drill^® to improve drilling efficiency, including:

• Changing BHP without changing mud weights saving circulation time
• Ability to apply a trip margin without changing mud weight
• Improved and simpler cementing operations via MPC
• Improved ability to convey completion strings to TD
• Longer Horizontal Sections drilled
• Reduced overbalance during logging runs improving logging results
• Reduced differential sticking condition

The MRL can be a fixed line installed as an auxiliary line on the riser above the SPM, a flexible hose, or a string of pipe run separately in the water.

EC-Drill^® takes suction from below the level of the fluid in the riser. This leaves a column of mud above the pump suction that would be static without the use of the top fill pump. The topfill pump takes suction from the active system and puts fluid at a controlled rate into the top of the riser, normally at the diverter housing. The SPM then returns both the fluid being pumped down the drillstring and the flow from the topfill pump. This causes a downward flow of fresh mud from active above the subsea SPM.

The required pump is normally placed such that it can take gravity feed from the active system and is controllable to a rate of 200-1200 lpm (50 – 320 gpm). It is commonly connected with the rig’s drilling control system and controlled by the driller.

The main equipment elements of EC-Drill^® are

• Subsea Pump Module (SPM) – instrumented pump system used to pump all mud and cuttings to surface.
• Control System – the computerized control system that controls and monitors the SPM and associated equipment allowing for precise control of fluid level in the riser and thereby well pressure

EC-Drill^® is a modular system that typically requires a 14ft Office Container, a 14ft Control Container, a Subsea Pump Module docked on the riser and an Umbilical reel.

The EC-Drill^® system can deliver sufficient flowrate for drilling in hole sections up to 26” or larger, the EC-Drill^® pump module is typically limited by shaker capacity ( 6000 lpm or 1580 gpm)

Yes, EC-Drill^® is engineered for Non Aqueous Fluid (NAF) or Water Based Mud (WBM)

No, EC-Drill^® does not interfere with any drilling BHA equipment. EC-Drill^® has been used with the major MWD/LWD/RSS system in operation without any issues.

With the popularity of EC-Drill^®, the equipment is subject to availability. With available EC-Drill^® equipment, the limiting factor will be rig integration time. The 3rd party modified riser joint is typically a longest lead item, with a usual lead time of 6 months, although 3 months lead time has been achieved on previous projects.

The EC-Drill^® system includes redundancy on critical equipment including riser pressure sensors (for monitoring riser level) and subsea electronics modules.

The riser level is monitored by two dual sensors, providing 4 independent riser pressure readings. The sensors riser level sensors have an accuracy of +/- 0.145 psi.

he desired riser level is set on the control system to fill up the riser with the EC-Drill^® system. The EC-Drill^® SPM reduces flowrate to allow the riser to fill with the mud flow from the drill string, top fill pump, and/or boost pump. This will depend on the most convenient method for the operation being performed.

The main items required to integrate EC-Drill^® onto the rig are

• Modified Riser Joint (MRJ) – this is a riser joint with port to allow EC-Drill^® to take suction from the riser, the modified riser joint also includes the Riser Isolation Valves (RIV) and the mounting for the EC-Drill^® Subsea Pump Module (SPM)
• Mud Return Line (MRL) – the conduit to convey Mud and Cuttings to surface from the SPM
• Surface lines – the surface line installation is minimal, consisting mainly of a mud return line with flow meter to the low pressure mud system
• Top fill pump – this is a small pump taking suction from active system and pumping into the top of the riser to provide a flow of mud to ensure the mud above the EC-Drill^® SPM is fresh and at the same density

The EC-Drill^® is typically docked on riser up to 500 m (1600 ft) below RKB irrespective of the water depth when greater than 500m. If the water is shallower than 500 m, it would be docked near the subsea BOP.

The EC-Drill^® system can control the riser pressure quite accurately, routinely the riser pressure can be controlled to +/- 1 bar (14 psi) through pump starts, stops and rate changes. More precise control is possible with controlled ramping of the mud pumps.

Both the umbilical and the mud return line are dry connected to the SPM in the moonpool.

The EC-Drill^® system does not make a major change to barriers and well control. The primary barrier to well flow remains the mud with density monitored. We add to this monitoring of the riser level with the redundant riser level sensors.

The secondary barrier remains the BOP, wellhead, casing and cement, and conventional well control procedures are used.

In addition to EC-Drill^®, Enhanced Drilling also offers RMR (Riserless Mud Recovery), a system to return top hole mud and cuttings to surface to allow re-use of the mud and volume monitoring of the top hole. Managed Pressure Cementing (MPC) can also be performed on top holes. In addition, our Cuttings Transport Service (CTS) allows for cutting and cement returns from top hole drilling to be directed to another subsea location if they cause an issue near the wellhead. These services can be combined with EC-Drill^® service with some common use of much of the same type of equipment.

The benefit of the EC-Drill® is limited in onshore wells. If you have room between the BOP and RKB for the EC-Drill® pump it could add the ability to quickly adjust BHP by 1-3 bar. To date we have not used the EC-Drill® CML system on an onshore well.

The power requirement for the main motors on the EC-Drill^® Subsea Pump system is 1200 amps of 3 phase 690 VAC. It is possible to accommodate other voltages including high voltage from the rig power supply.

The EC-Drill^® system has been qualified to DNV-RP-A203 -Qualification of New Technology
EC-Drill^® is certified to DNV-OS-E101 and can also be ABS certified.

The EC-Drill^® system has been approved for use by both PTIL in Norway and BSEE in the US.

Yes, it can completely replace the conventional MPD system. The CML system has certain advantages and disadvantages over Surface Back Pressure (SBP) and Continuous Circulation System (CCS).

Significant advantages over SBP are CML uses standard overbalance mud weights, not underbalance mud weights as with SBP. In addition, CML only requires having one mud system. SBP typically requires two mud systems, an under balanced drilling mud weight and an overbalance tripping mud weight. When changing between these operations significant time is spent to circulate in/out the mud systems, as well as the adding to the complications with logistics and mud pit space. SBP relies on applying pressure at surface which will increase the EMW at shallow depths in the well where fracture pressures are usually lower. SBP has the largest footprint and requires the most rig modifications compared to the other methods. CML is significantly less costly for rig integration and avoids using rig time for mud displacements and running/retrieval of the Rotating Control Device as needed with SBP.

A disadvantage is SBP can change the Bottom Hole Pressure quicker than CML as the chokes can adjust to instantly change the EMW downhole. However, Enhanced Drilling is currently implementing a riser isolation device to be used together with EC-Drill to increase the operational envelope for the system and take some of the benefits from SBP into the CML application. This will results in the EC-Drill having the best of both MPD solutions.

The same conventional well control practices are used with the EC-Drill CML system. If a kick should occur, then the BOP will be closed and choke and kill lines used to circulate out the kick. An overbalance mud density is used with CML, typically a higher mud density will be used then with conventional drilling to give increased overbalance margin.

​The motors are 4-poled and 300-450 kW each (different types). The flow range is up to approximately 6000 l/min, depending on depth and fluid weights.

We find it useful do have onshore training courses for the rig personnel and operator prior to use. In the past we have had used onshore simulators and our own offices for courses to train rig personnel. There is also training offshore for rigs and crews that are new to EC-Drill and CML.

Yes, the development of this is still going and we plan to do a pilot well in 2021.

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An ideal time frame would be 6 to 7 months to get a rig EC-Drill ready. The Modified Riser Joint is the largest lead item at around 4 months. Various rig modifications to flow lines, installing pad eyes, etc. are required.

EC-Drill^® is easy to include in well planning. The application of the system is simple and straightforward, with the desired riser level specified in the drilling program. The EC-Drill^® software includes the ability also to compensate for EC-Drill^® by automatically adjusting the riser level based on the pump rate. EC-Drill^® impact on the mud system is limited to optional increase in mud weight over that used conventionally.

Enhanced Drilling has a complete set of operating and contingency procedures available and can assist with required risk analysis.

When EC-Drill^® is included early enough in planning, there is a potential to alter casing settings depths, and to increase length of productive sections. The required well planning modifications can normally fit into the equipment lead time easily.

If the weather allows the riser to be run, then we can attach the pump to the riser. We have a Launch and Retrieval System in the moonpool that is used to attached and retrieve the pump module from the riser.

If the subsea pump fails then operations can always be continued conventionally, with a full riser and mud returns to surface.

If the subsea pump module is attached on the riser and EC-Drill is required for the section, then the riser will need to be pulled to the pump location to recover the pump.

If the subsea pump module is run separately on drill pipe or on cable, then it can be recovered with out pulling the riser. The pump can be replaced offline when run with cable or dual derrick rigs when run on drill pipe.

We are always moving forward with our technology and adapting to the market needs and requirements. Currently the existing technology covers a wide range of wells from shallow to ultra-deep waters, however we are continuously looking at how we can provide even larger margins and value for our clients.

This means placing the pump below the BOP. The principle would be the same, but we would need to qualify a fail-safe close outlet valve system, probably to a Safety Integrity Level 3. This is doable, but there needs to be a project with a business case for that development to move forward.  

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Our pumps cannot pump gas, so if a large concentrated influx gets as far as our pumps they will not be able to pump. In an influx situation, standard well control procedures will be used. Our latest development with a riser isolation device included will enable us to shut in above the pump and circulate the kick out without closing the BOP. Pilot well for this is planned for 2021.

The fluid level is controlled by our software and pumps on the riser. We can set the software to automatic mode to maintain a set fluid level in the riser or manual mode to adjust the fluid level as desired. If wired drill pipe is used this enables precise and continuous pressure measurements downhole, which can be used to control the fluid level. The fluid level is the riser is calculated by sensitive pressure sensors on the modified riser joint and the mud weight.

Pump housing is currently rated to 1000 psi / 69 bar.