Point Thomson Project: Separator Design for High Pressure Gas Cycling

SPE Alaska Section LuncheonBP Energy Center Anchorage, Alaska

Barry M. BoosExxonMobil Development CompanyPoint Thomson ProjectEngineering Manager

Adam Bymaster, ExxonMobil Upstream Research CompanyEd Grave, ExxonMobil Upstream Research CompanyJerad Naymick, ExxonMobil Development Company

November 9, 2010

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Project Overview• The Point Thomson project is expected to be the highest pressure gas cycling operation in

the world and the first such operation on the Alaska North Slope• The high pressure gas reservoir is located in a remote, arctic, and environmentally

sensitive area on the eastern Alaska North Slope • A cross-functional team from the ExxonMobil Upstream companies was formed to address

the key technical issue of high pressure separation

Point Thomson Central Pad March 2010

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Resource and Technical Development

• The Thomson Sand reservoir contains an estimated 8 TCF of gas • The Central Processing Facility (CPF) will be co-lo cated on the Central Pad with a

Thomson Sand producer and gas injector well pair– Designed to process 200 MMSCFD of natural gas and 1 0,000 BPD of associated condensate– Recovered liquids are stabilized and exported to a carrier pipeline for ultimate delivery into

the TransAlaska Pipeline– The gas from the inlet separator is compressed to g reater than 10,000 psia for re-injection

into the reservoir

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High Pressure SeparationKey Technical Issue:• The inlet production separator at the CPF will operate at 2,700 psia• Separator design and performance at high pressure• Potential liquid carryover into downstream equipment could result in damage

and critical failure of compressor units

Separation is typically driven by gravitational or centrifugal forces. As pressure increases, the interfacial tension and density gradients between the vapor and liquid phases decrease, which can have a significant impact on the separation characteristics, most notably droplet distribution, droplet shearing, re-entrainment, and film stability.

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Technical and Business Impact:

• High pressure separation (2,700 psi) will optimize the compression horsepower for re-injection

• Proposed design utilizes high capacity, compact separation technologies

• First stage separator is estimated to save 40-55% in footprint and 40+ tons (55%) in weight when compared to a conventional design

• Proving separation technologies at elevated pressures is essential to the development of remote and marginal oil and gas fields

High Pressure Separation

3D representation of Central Pad and separation mod ule.

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3D concept for high pressure test skid and proposed design for Point Thomson field.

Incoming Stream

Deliquidiser BypassDeliquidiser Cyclone

Vertical Scrubber Equipped with High Performance Internals

Deliquidiser Liquid Boot

Stage 1: Bulk V/L Separation

Stage 2: Gas Cleanup and Fine Droplet Removal

Compact Separation Technology

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Compact Separation TechnologyInline Deliquidiser• High capacity, high separation efficiency• Liquid load: 0-10 vol% • Gas turndown range: 50%• Low pressure drop• Open structure, not sensitive to fouling• Compact inline design saves considerable weight and space• More robust, easily and quickly installed – no vessel entry required

How it works: The liquid laden gas stream enters t he deliquidiser and is passed through a low pressure drop mixing element (1) to evenly distribute the l iquid present in the gas phase. A stationary swirl elemen t (2) brings the stream to rotation, causing the gas to migrate to the center of the cyclone while the liqu id forms a spinning film on the inner wall of the cycl one. The gas exits the cyclone through a smaller pipe within the main pipe (3). The liquid enters the ann ular space between these two pipes and is collected in a vertical boot section (4). A gas recycle (5) is in cluded to promote optimal liquid from gas separation.

(1) Mixer Element

(2) Swirl Element

(5) Gas Recycle

(4) Liquid Boot

(3) Vortex Finder, Anti-Swirl, & Expander

Image courtesy of FMC Technologies.

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High Performance Internals

• Evenflow vane inlet– Reduces the momentum of the incoming feed stream,

encouraging bulk liquid drop-out– Reduces droplet shearing– Minimizes liquid re-entrainment

at HLL interface– Provides even gas flow distribution

• Wire Mesh Agglomerator– Operated at flooded conditions to promote droplet

coalescence– Increases efficiency of the downstream mist

eliminating assembly – Increases turndown capabilities– Provides pressure drop, minimizing maldistribution

• SpiraFlow TM Demisting Cyclones– Provides high degree of separation

of fine droplets– Compact, high capacity mist eliminator

reduces vessel size and weight Illustration of scrubber internals and gas/liquid flow.

Images courtesy of FMC Technologies.

SpiraFlow TM Box

Mesh Pad

Inlet Vane

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Southwest Research Institute ® is the only facility in the world equipped to test at the desired pressures (up to 3,600 psia)

• Test Location: San Antonio, TX• Test Schedule: August-September 2010• Variables: Vessel Configurations

Flow RatesGas Volume FractionPressure

The separation test skid is a scaled down version o f the proposed field unit, equipped with the necessary co ntrols, instrumentation, and data acquisition system. The skid is 25ft (L) X 10ft (W) X 17 ft (H) and weighs 17 tons.

Key Goals• Ensure Safety – Nobody Gets Hurt• Qualify the proposed separation technologies at

high pressures• Quantify liquid removal efficiency of each

individual component and the entire system• Identify optimal operating window for design• Mitigate uncertainty and risk associated with the

design and operation

High Pressure Qualification at SwRI®

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High Pressure Qualification at SwRI®

Test Conditions• Pressure: 1500-2600 psia• Temperature: 90ºF• Gas rates: 0.5-2 ACFS• Liquid volume fractions: 0.03-20%

(0.25-120 gpm)

Test fluids• Flow loop charged with natural gas

and a hydrocarbon mixture with similar fluid properties of field fluid (density, viscosity, low surface tension)

Separation Equipment Qualified• Achieved required separation

efficiency under challenging Point Thomson conditions

High pressure separation skid during testing at SwR I®.

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Questions?Questions?Questions?Questions?