Assessment of Subsea Production & Well Systems

Final Report Submitted to the U.S. Department of Interior Minerals Management Service

(MMS), Technology Assessment & Research (TA&R) Program

Project Number: 424

by Dr. Stuart L. Scott, Principal Investigator

Deepak Devegowda, M.S. Student Ana M. Martin, Ph.D. Student

Department of Petroleum Engineering Texas A&M University

College Station, Texas 77843-3116

October 12, 2004

DRAFT

Executive Summary

A study has been completed which examined the technical, operational and safety issues

associated with subsea production and subsea well systems. The rapidly accelerating shift to

subsea production represents a significant departure from conventional production operations.

The subsea environment is perhaps the most remote and unexplored on earth. This remoteness

makes monitoring and intervention much more difficult and raises unique environmental issues.

Historically, subsea production and subsea well systems have had a good track record. However,

these systems are now being deployed in ways rarely encountered in previous development

schemes, presenting a number of technical challenges. One of the key challenges is to address

the expected poor primary recoveries from subsea wells. Subsea production systems require the

transportation of a multiphase mixture of oil, water and gas for many miles from the producing

well to a distant processing facility. Industry and regulators are increasingly becoming aware

that, while reducing up-front capital outlays, long, multiphase flowlines add additional

backpressure, reducing flow rates and ultimate recoveries. For example, conventional production

operations routinely drawdown wellhead pressures to 10-20 bar, while subsea completed wells

may have abandonment wellhead pressures over 100 bar due to the backpressure added by the

long multiphase flowline. One of the challenges posed by subsea production is how to reduce

wellhead pressure to allow effective recovery of hydrocarbon resources. To address this issue,

there is growing interest in processing the produced fluids subsea, to achieve improved

recoveries and greater efficiencies. A goal of this study is to provide decision makers with the

information necessary to assess the conservation impact associated with various subsea

production strategies; strategies that may or may not consider subsea processing or subsea

multiphase pumping.

The objectives of this study are shown to the 1) Subsea Processing

right. In pursuit of these objectives a team of 2) Flow Assurance

Texas A&M graduate and undergraduate students 3) Well Intervention 4) Long-Term Well Monitoring

conducted literature surveys and site-visits. In 5) Investigation of Factor Effecting Ultimate Recovery

addition, steady-state pipeline modeling was 6) Safety & Environmental Concerns performed using the PIPESIM program and 7) Technology Transfer

Executive Summary ii

transient modeling was performed using the OLGA simulator. These pipeline simulators were

also coupled with the ECLIPSE reservoir simulator to examine the overall performance of the

well/production system. Given in the following sections is a summary of the findings from this

study. First, the assessment of technology in the areas of subsea processing and flow assurance

are discussed. This is followed by considering well intervention and monitoring for subsea

systems. Results of the investigation of factors effecting ultimate recovery for subsea wells are

then outlined. To conclude, the major findings of this study are listed.

Subsea Processing

Subsea processing holds the potential to off-load fluid equipment to the seafloor. This provides

for reduction in platform/FPSO deck load requirements while also eliminating the backpressure

imposed by the production riser. Subsea processing can take several forms, comprising a myriad

of subsea separation and boosting scenarios. Table I shows the classification of subsea

processing systems used in this study. Strategic technologies that are believed to be essential for

the successful implementation of subsea processing include multiphase pumping, compact

separation and multiphase metering, which are all in varying stages of maturity.

Classification Characteristic Equipment Water Disposal Sand Disposal

Type 1 Multiphase Mixture is Handled Directly Multiphase Pump None...Pumped with Other

Produced Fluids NonePumped with

Other Produced Fluids

Type 2 Partial Separation of the Production Stream Separator and Multiphase

Pump; possible use of Wet-Gas Compressor

Possible Re-Injection of partial water stream, i.e.

"free" water

None..Pumped with Liquid Stream

Type 3 Complete Separation of the

Production Stream at Subsea Conditions

Separator and Scrubber Stages w/ Single or

Multiphase Pump; possible use of Gas Compressor

Re-Injection/Disposal of Majority of Water Stream Must be addressed

Type 4 Export Pipeline Quality Oil & Gas Multi-Stage Separator and

Fluid Treatment; single-phase pumps and compressors

Re-Injection/Disposal of Entire Water Stream Must be addressed

Table I: Classification of Subsea Processing Systems

Multiphase pumping represents the most basic type of subsea processing and hence the most

achievable. At present, multiphase pumping represents the only commercial form of subsea

processing. As described in Table I, multiphase pumping can be classified as a Type 1 subsea

processing system. It directly handles the multiphase mixture with a minimum of equipment.

Executive Summary iii

Multiphase pumps can also be used in conjunction with the other types of subsea processing

schemes. For example, the Type 2 subsea processing system makes use of partial separation

of the produced fluids. In this case a multiphase pump will still represent the best option for

pumping a liquid stream that will have some amount of associated gas. A multiphase pump or

wet-gas compressor will also represent the best choice for the gas stream. If the gas stream is not

left to flow under its own pressure, a multiphase pump or wet-gas compressor can boost

pressure of the gas stream even when it contains several percent liquid by volume.

While a relatively new area, subsea multiphase pumping has established an impressive track

record. The Table II shows a list of the various subsea multiphase pump projects underway or in

the conceptual stage. As can be seen the helico-axial technology is the established leader.

Subsea applications have tended to exhibit the high flow rates and moderate GVFs which are

ideal for this technology. In the past few years the twin-screw manufacturers have also

introduced subsea versions of these pumps. Twin-screw subsea multiphase pumps seek to

address the higher GVF applications and the applications where slugging can introduce brief

periods of high GVF after passage of the liquid slug. As can be seen, 2004 represents a

particularly active year with many new entrants into this field.

Pump Technology

Subsea Integrator

Product Designation

Pump Manufacturer Operator Year Field Status

Helico-Axial Framo Framo Framo Framo Framo Framo Framo

SMUBS ELSMUBS ELSMUBS ELSMUBS

FDS FSS FDS

Framo Framo Framo Framo Framo Framo Framo

Shell Staoil

ExxonMobil Hess Hess

Santos BP

1994 1997 1999 2002 2003 2004

new project

Draugon Lufeng Topacio

Ceiba Ceiba

Mutineer/Exeter W. of Shetland

1 pump 5 pumps 2 pumps 2 pumps 5 pumps 2 pumps

2 pumps considered

Twin-Screw Technip Sonsub

Curtiss Wright

HYDRA/ELECTRA DMBS

SBMS-500

Sulzer & IFP GE/Nuovo Pignone

Leistritz

N/A Agip

Petrobras

2004 1997

1996-present

N/A offshore Italy

Marlim

conceptual N/A

3rd onshore qualification test underway at Atalaia

Aker/Kvaerner SMPM Bornemann Demo 2000 2001-2002 K-Lab tested w/ condensate & methane

Aker/Kvaerner SMPM Bornemann CNRL 2004 Balmoral schedule for 4Q installation

Bornemann UW Bornemann Wintershall 2004 onshore sour gas field in Germany onshore pressurized

testing as part of German MPA research program

Subsea7 MPSP 1500 Flowserve Total new project W. Africa conceptual Oceaneering N/A CAN-K N/A new project N/A conceptual -

adapting downhole high pressure technology

Piston Hydril N/A Hydril N/A new project N/A conceptual - adapting subsea mudlift technology

Table II: Status of Subsea Multiphase Pumping

Executive Summary iv

Another area of interest for subsea multiphase pumps is that of speed control. While traditionally

the industry has relied on variable frequency drives (VFDs), the large size of the subsea

multiphase pumps has generated interest in the use of torque converters for speed control. These

devices become cost effective for large applications (greater than 500 hp) and may offer some

advantages for subsea operations. The ability to place the speed control equipment on the

seafloor rather than on a floating platform may provide cost savings. Also the cold deepwater

temperatures will be able to dissipate any heat generated by the torque converter. In March 2004