closed loop circulation system for mpd

8/12/2019 Closed Loop Circulation System for MPD

http://slidepdf.com/reader/full/closed-loop-circulation-system-for-mpd 1/13

MINIMISING DEEPWATER DRILLING ENVIRONMENTAL EXPOSURE ANDINCREASING OPERATIONAL EFFICIENCY IN NEW ZEALAND WITH

CLOSED LOOP CIRCULATION DRILLING

Julmar Shaun Sadicon Toralde and Chad Henry WuestWeatherford (Solutions) Sdn. Bhd.Level 25, GTower, No. 199 Jalan Tun Razak

50400 Kuala LumpurMalaysia

[email protected] / [email protected]

ABSTRACT

Closed-loop circulation drilling (CLCD) systems provide a better alternative to open-to-the-atmosphere conventional drillingsystems in deepwater applications by emphasizing the use of closed and pressurizable systems to allow a scalable approach

that produces a range of benefits from increased personnel and environmental safety to better data resolution and evengreater operational control over the drilling process. This technical paper discusses how CLCD addresses a need in a post-Macondo world where deepwater drilling is under intense and increased regulatory control by providing flexible systems thatsupplement the safety and efficiency of deepwater drilling operations. It also enumerates the lessons learned from recentsuccessful applications of this technology in the Asia Pacific region as well as provide details of how CLCD systems can beinstalled and utilized on moored and dynamically positioned drilling vessels deployed for deepwater conditions in NewZealand.

KEYWORDS

Closed-Loop Circulation Drilling (CLCD), Managed Pressure Drilling (MPD), Rotating Control Device (RCD), Early Kick and LossDetection (EKLD), Deepwater, Drilling, Dynamically Positioned, Drilling Operational Efficiency, Environmental ExposureMinimization, New Zealand.

INTRODUCTION

The term Closed-Loop Circulation Drilling (CLCD) has been used to denote any drilling operation that is performed in a closedenvironment instead of the prevalent method of keeping drilling fluid returns open to the atmosphere. In conventional drilling, theonly instance that a well is closed and can perform closed loop circulation is when the blow-out preventers (BOPs) are closed, aswhen an influx is taken. Closing the well in allows for backpressure to be imposed on the system using the rig well control chokes inorder to increase bottomhole pressure and control and circulate the influx out. However, drilling, or rotating in particular, cannotbe performed in this instance as the rig BOPs are not designed for rotation through them while in the closed position.

A rotating control device (RCD; Fig. 1), when installed, provides drilling operations with the ability to close or restrict the flow ofcirculation returns and control and maintain pressure on the well while at the same time being able to rotate and continue drilling.It is the minimum requirement to be able to put a CLCD system in place. Figure 1 shows the two major components of an RCD: (1)the RCD bearing assembly; and (2) the RCD body that it is installed on.

An RCD, according to the American Petroleum Institute (API) specification for this type of equipment, API 16RCD, is ‘a drillthrough device with a rotating seal that contracts and seals against the drill string (drill pipe, casing, kelly, etc.) for the purpose ofcontrolling the pressure or fluid flow to surface’ (2005). It creates a pressure-tight barrier in the wellbore annulus that enables youto contain and divert returning fluids, forming a vital line of defense against drilling hazards, such as kicks and shallow gas(Weatherford, 2011c). RCDs can either be active or passive, but passive types that use rubber elements which stretch-fit to thetubular passing through it, are predominantly used in CLCD systems.

mailto:[email protected]









CLOSED LOOP CIRCULATION DRILLING

CLCD systems are scalable. They can be made to suit the application they will be used for. Figure 2 features the scalable nature ofCLCD systems and it shows that the benefits of CLCD applications can be grouped into three types, namely: (1) safety andefficiency; (2) visibility; and (3) control. The benefits increase as the scale of the CLCD installation increases.

With only an RCD installed in a CLCD system, only safety and efficiency benefits can be attained, while if the RCD is used inconjunction with an early kick and loss detection (EKLD) system, particularly a mass flow meter, increased visibility of drillingevents can be provided in addition to those already available. Furthermore, when used with an automated choke manifold, thecomplete range of benefits is received, with full control of the annular pressure regime of the well included, making the applicationof managed pressure drilling (MPD) possible (Pavel, 2011).

A CLCD system with only an RCD involved provides safety and efficiency by diverting fluid away from the rig floor and frompersonnel working on top of it, keeping people away from the line of fire should hazardous gases and substances be inadvertentlyreleased from the well. It also allows pipe movement even with pressure on the well, thereby mitigating the occurrence of stuckpipe. From an environmental standpoint, since the RCD facilitates CLCD, it minimizes the potential for fluid spillage around thewellhead associated with open-air systems and the RCD sealing element also wipes the drillpipe clean as it is tripped. However, thevisibility of the conventional drilling system is not improved as an influx or loss can still only be monitored by pit volumes and ECDcontrol is done manually or by conventional well control via BOP.

For increased visibility, an RCD is used in conjunction with a mass flow meter, which utilizes techniques that measure the massflow of the flowing stream, for accuracy and reliability reasons. In these Coriolis-type meters, the mass and density, includingtemperature, are measured directly and flow is calculated from these acquired values. A Coriolis mass flow meter has a pressuredrop and as such must be installed in a system with closed pipe work and is not ideal for use in gravity-based flow systems back tothe shale shakers, which is one of the reasons why they are being used in combination with closed well bores and choke manifolds(Nas 2011b). With the RCD and the flow meter installed, the CLCD system provides safety and efficiency by acting as an early kickand loss detection system through accurate mass balance monitoring. Pavel and Grayson (2011a) state that closing the loop createsa contained circuit of the incompressible drilling fluid, so that a small change in bottomhole pressure due to a wellbore influx orloss is transmitted by the fluid to the surface in seconds and also allows for easy measurement of fluid flow, allowing the detectionof minute circulating losses or gains. Ballooning and wellbore breathing can also be more accurately diagnosed using the system ifflow fingerprinting was performed beforehand. The CLCD EKLD set-up is provided in Figure 3. There is however, still no controlinvolved, and manual ECD control or conventional well control via BOP will have to be performed to act on the events identified.

Full control of the annular pressure profile of the well is provided with the addition of an automated MPD Choke Manifold(Figure 4). With this equipment, which utilizes Microflux Control technology, application or release of backpressure exerted on thewell using automated chokes can be performed, thereby making immediate adjustments to the bottomhole pressure while drilling,and consequently MPD possible (Weatherford, 2011b). In addition to this, the high-precision sensors for flow and pressure(standpipe and surface backpressure) values that are installed in the manifold provide greater data resolution that further enhance

the safety and efficiency of the drilling process.MPD is defined by the International Association of Drilling Contractors (IADC) as ‘an adaptive drilling process used to moreprecisely control the annular pressure profile throughout the wellbore’ (2008). Its objectives are: (1) to ascertain the downholepressure environment limits; and (2) to manage the annular hydraulic pressure profile accordingly. Compared to underbalanceddrilling operations, MPD does not intentionally allow the well to flow to surface, but it will nonetheless be equipped to handle thesame should it occur (IADC, 2008; Weatherford, 2011a).

With a CLCD system, the Constant Bottomhole Pressure (CBHP) variant of MPD can be employed. In this method, backpressureis used to be able to compensate for the annular friction pressure lost when the rig mud pumps are turned off during drillpipeconnections, allowing drilling operations to continue in wells with narrow mud weight windows. This highlights the added factor ofbackpressure that CLCD and MPD brings into the bottomhole pressure equation, as compared to conventional drilling where onlythe hydrostatic pressure of the drilling mud and the annular friction pressure control bottomhole pressure. Additionally, makingchanges in drilling fluid density takes a long time to institute and in the case of drilling pump rate, reducing it will have holecleaning consequences. Backpressure as imposed by the automated MPD choke manifold, on the other hand, can be changed easilyand fast, as changes made to the choke opening, are immediately relayed downhole at the speed of sound, thereby adjusting theeffective bottomhole pressure quickly and enhancing greatly the degree of control exercised over the behavior of the well (Paveland Grayson, 2011b, 2011c, 2011d).

CLCD systems provide a wide range of applications and benefits that are simply not possible with conventional open-to-the-atmosphere drilling systems. Moreover, in recent years, these applications have been utilized and benefits have been enjoyed inboth onshore and offshore drilling applications in the Asia Pacific region (Nas et al, 2009). However, entry of the technology intothe deepwater environment, particularly in deeper water depths that require drilling vessels that have dynamic positioningcapabilities has been until recently slow. The next section discusses how CLCD systems have been adapted to the deepwatersetting.



ROTATING CONTROL DEVICES FOR DEEPWATER CLCD OPERATIONS

In onshore and offshore applications involving surface BOP stacks, the RCD is normally installed directly on top of the rigannular BOP. For operations involving subsea stacks, which is the case for deepwater wells, it is normally deployed on top of acollapsed slip joint and above the tension ring when a moored drilling rig is used, while on a dynamically positioned rig, it ispositioned below the tension ring and integrated with the rig riser system. Figure 5 shows the typical set-up for recent deepwaterMPD operations using a submerged RCD. Toralde (2011) has written on the history behind the development of the said RCD, aswell as how it makes CLCD or MPD possible in deepwater DP drilling vessels because of the following innovations:- Installation in riser below waterline and above the termination joint for the subsea choke and kill lines.- Rated to a tension rating is 3 million lbs, since it is now installed under the tension ring.- Gives the MPD system a higher pressure rating, as it is no longer limited by the pressure rating of the collapsed slip joint used in

previous systems.- Preserves the rig’s heave compensation system, as the slip joint is no longer collapsed.- Allows rig rotation by keeping MPD hoses away from tension lines.- Safer MPD system installation, as the whole assembly fits through the rig floor and minimizes the time required with personnel

in the moonpool area.This set-up has already been deployed (see Figure 6) on eight rank wildcat deepwater wells in Indonesia on the dynamically

positioned GSF Explorer drillship to perform MPD from 2010 to 2012. The system has been utilized to conduct almost all types ofCLCD and MPD operations, ranging from EKLD, PMCD and CBHP, and has been used in almost all the different stages of the wellconstruction operations, except during the riserless drilling phase. There were no major issues encountered with the use of theMPD system, and it has successfully adapted to the requirements of each and every well it has been installed in. Issues relating tothe use of the riser to hold pressure were addressed beforehand with the conduct of a riser analysis, to determine the maximumpressure that can be contained and possible failure points, and the setting of limits.

The RCD used for the deepwater MPD operations in Indonesia was of the Below-Tension-Ring (BTR) type. The RCD forms partof what is called an MPD riser joint (together with a surface annular BOP and a flow spool) that is installed through the rotary tablewhen the riser and BOP are deployed. The BTR RCD was installed above the intermediate riser joint and below a standard slip jointabout 43 m (140 ft) below the rig floor and 12 m (40 ft) below sea level. Hydraulic and electrical connections below the water linewere made via a subsea-rated hydraulic stab plate. The BTR RCD is the first rotating head designed and field tested to support risertension requirements of as much as 3 million lbs. and is certified to the drill-through specifications of API 16 RCD, the industrystandard for RCDs. Using this standard, the RCD has been rated to a static and dynamic pressure ratings of 2,000 psi and 1,000 psi(at 100 rpm), respectively.

Prior MPD operations aboard floating vessels have been configured with a surface RCD above the water line and the tensionring. Because the new RCD is made up below the tension ring, no modifications are required to the riser’s telescoping slip joint orthe rig’s mud returns system. In the deepwater CLCD set-up, an MPD annular BOP is installed below the BTR RCD. The MPD annular

BOP is used in conventional drilling operations when the RCD sealing element is not installed to shut the well in and facilitate CLCDriser degassing operations. The MPD annular BOP also can be used when the RCD sealing element needs to be replaced. The MPDflow spool is installed below the MPD annular BOP and is connected to flexible hoses, which act as the primary flow lines for MPDoperations.

RECENT DEEPWATER RCD SYSTEM DESIGNS

Recent technological developments related to RCD systems for deepwater MPD use have mainly involved two new designs: (1) asubsea rotating device (SRD) for dual gradient drilling (DGD) use; and (2) a mechanical version of the BTR RCD.

According to Barry (2013), the newly developed DGD system that will be deployed on a DGD-capable drillship is currentlyundergoing system integration testing (SIT) prior to deployment in the GoM, and is of the seabed-pumping DGD category. IADCdefines Dual Gradient Drilling (DGD) as a subset of MPD used in subsea applications to manage the annular pressure profile bycreating multiple pressure gradients. A key component in the new DGD system is the industry's first commercially available subsearotating device (SRD), shown in Figure 7, which diverts drilling fluids to establish a dual gradient environment. SRD is installed ontop of the DGD system that sits on top of the LMRP and subsea BOP and it diverts annular return fluids before they enter the riser. Itis a highly modified subsea RCD; instead of the latch mechanism being in the housing, it was added to the bearing assembly itself.The SRD bearing can now be set and released mechanically for maintenance and to provide full bore access through the riser. Itforms an annular seal between the wellbore and the riser that allows running and rotating the drill pipe while diverting the flow ofreturns. Below the SRD seal are drilling mud and cuttings; above the seal in the riser is a lightweight fluid. This isolation of theannular fluid column into two discrete fluid components that eliminates the weight of several thousand feet of drilling mud in theriser that would otherwise put pressure on the wellbore.

The mechanical version of the BTR RCD or the BTR-M (Figure 8) integrates salient features of the SRD into an RCD installationthat can be deployed just below the rig tension ring. The system will have a smaller MPD joint effective outer diameter (OD) thatallows installation of the system through the rig floor as well as a smaller RCD bearing assembly effective OD that will allow it towork on riser systems with smaller internal diameters, facilitating the running of the bearing assembly and its installation on the



RCD body or housing. The new BTR-M design does not require any major modification of rig systems for integration, as it does notrequire a termination joint, as choke, kill, booster and mux lines can now bypass the MPD / riser degassing joint and does notinvolve change out of the rig slip joint, riser, diverter to facilitate MPD. It also does not require extension of the rig choke and killlines, since termination of the same will now be as conventionally practiced.

CLOSED LOOP CIRCULATION DRILLING IN DEEPWATER

There are many drivers for the adoption of CLCD in the deepwater setting and they vary based on the requirements of thedrilling operation. Reasons previously used for justifying the use of the technology have been based mainly on either provision of ameans of drilling difficult wells or on improvement of the economics of the drilling operation:- To optimize the drilling process by drilling with a closed-loop circulating system.- To be able to utilize the Constant Bottomhole Pressure (CBHP) variant of MPD when narrow mud weight windows and wellbore

ballooning are expected or encountered during drilling.- To be able to conduct Pressurized Mud Cap Drilling (PMCD) in the event that severe circulation losses are encountered when

drilling through fractured carbonates.However, more recently, CLCD is helping address a need in a post-Macondo world where deepwater drilling is under intense

and increased regulatory control by providing flexible systems that supplement the environmental compliance, safety andefficiency of deepwater drilling operations. As a consequence, the following reasons have now been used for using deepwater MPDtechnology in certain projects:- To provide an early kick and loss detection system, especially when drilling deepwater exploration wells or hunting / pecking

for casing point in carbonate formations.- To enhance the riser gas handling system of the rig by allowing early detection of riser gas breakout and facilitating pressure

control for the same.Barry (2011) recently wrote about managing the threat of riser gas using CLCD methods, particularly utilizing an RCD

integrated with the riser for riser degassing purposes. Figure 9 shows a general historical view of MPD Market Acceptance showingthe trend towards utilizing CLCD as a means of mitigating risks, including those related to environmental compliance, andincreasing operational safety in deepwater operations.

It is also interesting to note that an independent study performed in 2009 by Jablonowski and Polio and sponsored by theUniversity of Texas at Austin proved that RCDs play a critical role in reducing the risk of major well incidents. The analysis ofonshore drilling data from a 12-year period (1995 to 2007) revealed a strong correlation between the use of RCDs and a reducedrisk of blowouts (Jablonowski and Polio, 2010).

RISER GAS HANDLING IN DEEPWATER DRILLING OPERATIONS

In a deepwater drilling environment, one of the hazards that CLCD systems help mitigate is the threat of riser gas and the risk ofreleasing large amounts of drilling fluid into the environment when diversion is required during a riser degassing event. Previousstudies on deepwater wells have revealed that due to the use of oil-based fluids, gas kicks that are unintentionally entrained in thereturn mud flow are unlikely to break out of solution until they reach a depth of 610 m to 915 m (2,000 ft to 3,000 ft) below thedrill floor. At this point subsea BOPs will no longer be able to contain them as deepwater wells are by definition in water depths ofmore than 500 m (1464 m). The conventional practice of dealing with gas in the riser is to use the rig diverter system to vent it, butthere is minimal control and considerable risk involved. It is for this reason that handling of gas in the riser on a deepwater rig iscomplex and challenging.

To mitigate this risk using CLCD systems, an RCD is installed on top of the rig marine riser together with an additional annularBOP and flow spool directly below it. This combination provides a system that is already in place to safely divert fluids containinggas away from the rig floor and toward an automated MPD choke manifold system. An in-line gas chromatograph and a high-ratemud - gas separator provide gas characterization and gas handling capabilities, respectively.

The CLCD system for deepwater applications on a DP vessel takes both a proactive and reactive approach on mitigating the riskof an event involving gas in the drilling riser. The proactive approach uses the early kick detection and control capabilities of theCLCD system to drastically cut back the incidence of reservoir gas entering the oil-based mud system at depth and dissolving into itwithout being detected, only to come out of solution later on when already in the drilling riser and above the subsea BOPs. Bothtesting and field deployment have proven the CLCD system’s ability to detect flow anomalies within its defined range earlier andfaster than conventional systems. The automated MPD choke manifold system is operated in automatic mode and will immediatelydetect a kick and close in on its choke to increase the bottomhole circulating pressure and control the well. In the unlikely eventthat an influx does make it above the subsea BOPs and into the riser with the CLCD system installed, the system is set-up so that itcan use the automated MPD choke manifold to circulate the influx out of the well in a controlled manner (Toralde and Karnugroho,2012).

In the eight rank wildcat deepwater wells drilled with the CLCD system in Indonesia, there have been no instances recordedwhere formation gas has broken out of solution above the BOPs and inside the riser. Furthermore, the CLCD system controlalgorithms detected at least five flow anomalies, kept them to a minimal volume, and circulated them safely out using the rig well



NAS, S. W., TORALDE, J. S. S., AND WUEST, C. H., 2009—Offshore Managed Pressure Drilling Experiences in Asia Pacific. SPE/IADCDrilling Conference and Exhibition, Amsterdam, The Netherlands, 17–19 March, SPE/IADC 119875.

PAVEL, D., 2011—Closing the loop alleviates challenges. Hart’s E&P Magazine, October 2011.

PAVEL, D. AND GRAYSON, B., 2010—Closed Loop Circulating – Part 1: Advanced pressure control improves kick, loss detection. Oiland Gas Journal. December 6, 2010.

PAVEL, D. AND GRAYSON, B., 2011—Closed Loop Circulating – Part 2: Manual pressure management enhances safety, efficiency. Oiland Gas Journal, January 3, 2011.

PAVEL, D. AND GRAYSON, B., 2011—Closed Loop Circulating – Part 3: Automation provides SCADA level safety, efficiency. Oil andGas Journal, February 7, 2011.

PAVEL, D. AND GRAYSON, B., 2011—Closed Loop Circulating – Part 4: Data benefit completion design, field development. Oil andGas Journal, March 7, 2011.

TORALDE, J. S. S., 2011—RCD for DP Drillship takes MPD Deeper. Drilling Contractor, July / August 2011.

TORALDE, J. S. S. AND KARNUGROHO, A., 2012—Riser Gas Risk Mitigation on a Drillship Uses Closed-Loop Circulation DrillingSystems. Hart’s E&P, May 2012.

WEATHERFORD, 2011—Managed Pressure Drilling Capabilities Brochure.

WEATHERFORD, 2011—MicroFlux Control Brochure.

WEATHERFORD, 2011—Rotating Control Devices Brochure.



FIGURES

Figure 1. Rotating Control Device (Passive Type).



Figure 2. Scalable Nature of Closed Loop Circulation Drilling.

Figure 3. Closed Loop Circulation Drilling Set-up for EKD. RCD installation is above the tension ring.



Figure 4. Automated Managed Pressure Drilling Choke Manifold.

Figure 5. Closed Loop Circulation Drilling Set-up for MPD. RCD installation is below the tension ring.



Figure 6. Actual deployment of the Below Tension Ring RCD.



Figure 7. Dual Gradient RCD.



Figure 8. MPD Riser Joint with the Below Tension Ring – Mechanical (BTR-M) version of the RCD.

Adapter Spool

Marine SeriesRotating Control Device (RCD)

Model 7875 BTR-M(Below Tension Ring – Mechanical)

Drill StringIsolation Tool (DSIT)

MPD Flow Spool

Adapter Spool

closed loop circulation system for mpd

Documents