Dual Gradient Drilling Basic Technology Lesson 2 Key Success Factors in DGD Jerome J. Schubert Hans C. Juvkam-Wold

Introduction Success Factors in Equipment Success Factors in Drilling Operations Success Factors in Well Control

Success Factors in Equipment Riser Return line Achieving dual density Cuttings processing unit Isolation of mud from seawater Managing the u-tube

Riser No Riser Conventional Riser Other Phantom riser Super straw Cork/Snapper Holy riser Top drum/tulip

Return line Riser Free standing Choke & Kill line Boost line Separate return line

Achieving dual density Gas lift Glass beads Water-jet pump Centrifugal pump Positive displacement pump

Positive displacement pumps Progressive cavity pumps Reciprocating Piston or Plunger pumps Diaphragm pumps

Diaphragm pumps Constant discharge rate High efficiency Large volume displacement Good HP rating Low pressure surges Can handle mud, gas, and solids

Pump Design Criteria Maximum output GPM Maximum output HP Maximum pressure Maximum mud density Need to get the pump rate, hp, pressure, etc of mlp

Pump Controls Match subsea pump rate with surface pump rate Automatic pump operation vs. manual controls Reaction time for start, stop, change in rate Subsea seawater pressure sensor Subsea mud reservoir level sensor

Pump Redundancy What can be done if one or more of the pump chambers fails?

Pump power Hydraulic power Electric motors to run hydraulic pumps Hydraulic fluid pumped from the surface

Solids processing unit System must handle solids in some way Pump ok How about plugging choke/kill and return lines?

Isolation of mud from seawater How do we separate mud in the annulus from the seawater either in the riser or open ocean? SRD Pressure rating Active for tripping, running casing, logging, etc.

Managing the u-tube How will we handle the u-tube? Write all procedures compensate for the active u-tube? Build a DSV to manage it?

DSV design factors How is it going to open and close? Will it have an adjustable opening pressure? Will it pass MWD signals and LCM? What will it do to circulating pressures? Are the opening and circulating pressure repeatable? Where will it be located in the drillstring?

Success Factors in Drilling Operations Lower riser loads Lower deck loads Lower deck space requirements Drill to TD with fewer casing strings

Success Factors in Drilling Operations Balanced Cement Plug Running Casing Cementing Check for Underbalance Circulation Connections Dual to Single Density Conversion Routine Drilling Start-Stop Circulation Tripping Unplanned Shutdown Fishing Logging

What a Dual Gradient Drilling System Must Be Able To Do For Effective Well Control ATM

Outline Understanding DGD Well Control - what is different ? How can we educate ourselves and develop a detailed understanding? What must an effective DGD well control system be able to accomplish? What must an effective DGD system contain?

Understanding WC in DGD Accept that DGD Well Control is not a simple task - it is different - and it is frequently neither intuitive nor obvious for example U-tubing - how does it affect kick detection? - how can we ensure that a constant bottom- hole pressure is being maintained? - what if power fails during WC operations? More details later . . .

~SEAWATER HYDROSTATIC PRESSURE U-Tubing in DGD FLOATER ~SEAWATER HYDROSTATIC PRESSURE STATIC FLUID LEVEL BOP PUMP Even with a DSV there is still a potential U-tube ATM 23

Outline How can we educate ourselves and develop a detailed understanding?

How can we Educate Ourselves? We have found that detailed hydraulics modeling is essential to understanding DGD Study each aspect of the process in detail: - Four PhD and seven MS studies have been completed or are in progress at Texas A&M! Detailed procedures had to be developed to cover all essential drilling and WC operations Procedures are critically peer reviewed and tested against the hydraulics model

Outline What must an effective DGD well control system be able to accomplish?

WC System must be able to: Avoid kicks - as far as possible Detect Kicks early - to minimize their size Determine kick size and Intensity Measure new formation pressure (“SI-BHP”) Safely remove kick from hole Maintain constant BHP Detect equipment failures during WC operations Provide contingencies for all potential failures

Avoiding Kicks Recognize the signs of increasing pore pressure? How? Allow the recovery of cuttings of sufficient size to evaluate their characteristic shape and other properties? Allow you to maintain satisfactory BHP during connections? While tripping? When cementing? When power fails?

Detecting Kicks Early Can you perform a conventional flow check? How accurate is your pit gain indicator? What other kick detection methods are available? What is the smallest kick that can detect? How quickly can you stop the influx? How? How do you handle the U-tube to ensure that its effects are not confused with kick indicators?

~SEAWATER HYDROSTATIC PRESSURE Dual Gradient Drilling System FLOATER Surface Pump Seafloor Pump ~SEAWATER HYDROSTATIC PRESSURE SEAFLOOR BOP PUMP How are you going to handle this kick? KICK ATM 27

Determining Kick Size What is the initial size of the kick when its presence is first confirmed? What is the size of the kick when influx stops? How can you measure kick volume and intensity? How can you maintain constant BHP - while circulating the kick out of the hole? - if you can’t circulate and kick is migrating? What is the Expected Kick Fluid Behavior?

Gas Kick Behavior As the gas kick moves up the hole the pressure generally decreases so we would expect the gas volume to expand - but how fast? At the seafloor pump there is an increase in pressure - how does the volume behave? Can we continue to assume that PV = const? Or should we use PV = ZnRT? We will take a closer look!

Outline What must an effective DGD system contain? - Essential Equipment?

Can we maintain safe well control with all of these methods? Which DGD System? There are basically two different methods we can use to Reduce annulus pressure at seafloor: Install pump at seafloor Inject a low density fluid in the return line Gas (e.g. air or nitrogen) Low density particles (e.g. hollow spheres) Can we maintain safe well control with all of these methods?

~SEAWATER HYDROSTATIC PRESSURE Dual Gradient Drilling System FLOATER Surface Pump Trip Tank(s) Mud Tanks, etc ~SEAWATER HYDROSTATIC PRESSURE Or gas or bead injector SEAFLOOR BOP Seafloor Pump Seafloor Pump - Power Transmission - Sensors - Controls Seafloor Choke? - Backup? Coordination between the pumps? - Instrumentation KICK ATM 27

In Summary ... What are the Key Factors that will ensure safe and efficient DGD Drilling and Well Control?

Key Success Factors for Well Control in DGD? Kick Detection Kick Containment (stop flow into well) Kick Removal (circulate kick out of hole?) Determine New Pore Pressure (after kick) Increase Mud Weight in hole (if necessary) Perform Leak-off Test

Key Success Factors - cont’d Manage the “U-tube” Detect and Manage Trapped Pressure Use Driller’s Method Perform Volumetric Well Control Manage Kick Expansion (pump very slowly) Manage Loss of Pumping Capability Understand the Behavior of Gas Kicks

Additional Success Factors Tripping Logging Running Casing Cementing Casing Setting Cement Plugs, etc. Handle Non-water Based Drilling Fluids…

Jerome J. Schubert Hans C. Juvkam-Wold Key Success Factors in DGD The End Jerome J. Schubert Hans C. Juvkam-Wold Key Success Factors in DGD