MPFM for Storage Gas Applications

Optimizing Gas Storage Fields Operation through High Accuracy Multiphase Flow Metering

N. Bonavita - G.Ciarlo (ABB Italy), P. Ciandri (TEA Sistemi SpA)

International Flow Measurement Conference 2015: Advances and Developments in Industrial Flow Measurement1-2 July 2015

MPFM for Gas Storage Applications

Underground Gas Storage (UGS) Generalities

Multiphase Flowmetering for UGS Operation Improvement

Innovative Multiphase Metering

Field Results

Conclusions

Agenda

November, 2014© ABB Group

| Slide 2


Underground Gas Storage (UGS) is a key sector for assuring reliable and efficient Natural Gas (NG) transmission and distribution

UGS provides a number of social and economic benefits, including:

Balancing of gas supply and demand over fluctuating market situations;

Supply NG under optimal economic conditions;

Ensuring gas supply even in case of failures or malfunctions

UGS Generalities

November, 2014 | Slide 3© ABB Group


UGS can take place in three different environments:

Depleted O&G reservoirs (~75% of UGS sites)

Aquifers (<10% of sites)

Salt caverns (~15% of sites). Usually the smaller in size but gaining relevance because ideal solution for peak load storage.

UGS Generalities


Global gas storage capacity is expected to grow consistently over the next 15 years both in emerging and in mature markets

Gas storage related investments are estimated in around €120 billions by 2030


A USG facility is designed in order to operate in two main modes:

UGS Generalities


Gas injection (summer) Gas extraction (winter)


Because the injected gas comes from the distribution grid, it can be safely considered as dry

However, when the gas is withdrawn, it will be contaminated by water and liquid hydrocarbons which must be removed before being supplied back into the distribution grid

MPFM for UGS Operation Improvement


UGS operators must afford additional gas processing including:

Removal of free liquid

Gas dehydration

Because the amount of liquid into the withdrawn gas is not known, the gas dehydration cannot be tailored to the actual need in order to guarantee operation compliance


Free Liquid is removed by means of bi-phase separators

Gas Dehydration may happen through 3 processes: Absorption (TEG), Adsorption (solid dessicant), Condensation

If free liquid suddenly increases in an extraction well, separator could not be able to manage and flood the dehydration column

This would prevent direct re-injection into the distribution grid

The measurement of on-line free liquid in withdrawn gas would provide a number of benefits:

Monitoring wells behavior

Avoiding to reprocess or overprocess the gas

Reducing environmental impact

MPFM for UGS Operation Improvement



Measuring liquid into gas is a typical multiphase metering task

However commercial Multiphase Flowmeters are unfit for Gas Storage applications for specific reasons

Very low accuracy when GVF is extremely high (>99,5%)

Lack of bidirectional capability

Scope of this talk is to introduce the new meter VIS based on isokinetic sampling, a technology which has proved to effectively tackle the UGS challenges

An Innovative MPFM


VIS, acronym for Vega Isokinetic Sampling, is the evolution of a previous, larger and heavier meter (named Vega)

VIS is a compact meter which can be directly inserted on pipelines for topside onshore and offshore applications

It is based on a unique and patented technology: the isokinetic sampling method

The only requirement is that multiphase stream should flow vertically downward

MPFM for Gas Storage ApplicationsAn Innovative MPFM


The IS method, allows the extraction of samples from the main flow without modifying the flow field around the probe.

IS conditions are established by adjusting the ratio between pressure drops through the multiphase orifice in presence of sampling, ΔpTP,S and without sampling ΔpTP:

∆𝑝𝑝𝑇𝑇𝑇𝑇, 𝑆𝑆

∆𝑝𝑝𝑇𝑇𝑇𝑇= 1 − 𝑟𝑟𝑟𝑟 2

Where rA is defined as the sampling ratio, (i.e. the ratio between the main pipe and the sampling probe sections):

𝑟𝑟𝑟𝑟 = 𝑟𝑟𝑇𝑇/𝑟𝑟𝑆𝑆

From the equation modeling the flow through an orifice plate:∆𝑝𝑝𝑇𝑇𝑇𝑇, 𝑆𝑆

∆𝑝𝑝𝑇𝑇𝑇𝑇= 1 −

𝑞𝑞𝐺𝐺𝑄𝑄𝐺𝐺

2

The extracted portion is then separated into liquid and gas phases by means of high efficiency swirl separators and measured with single phase techniques.

Total flow rates are then easy to derive: 𝑄𝑄𝐺𝐺 = ⁄𝑞𝑞𝑔𝑔 𝑟𝑟𝑟𝑟𝑄𝑄𝐿𝐿 = 𝑞𝑞𝐿𝐿/𝑟𝑟A



| Slide 10



11

Q1= Q0

Qs=0

Q0

DP

∆P0=αQ02

∆P1=αQ12=α(0.9)2Q0

2

1

2

∆P1∆P0

= 0.81

Q1= 0.9 Q0

Qs= 0.1 Q0

Q0

DP


IS technology has proved to be perfectly fit to manage UGS metering needs.

Because of its unique design it is able to:

Detect even minimal traces of liquid entrained in the extracted gas (LVF ≈ 10-4 %)

Cover the two different operating conditions:

During gas injection, it provides a measurement of the dry gas by means of the internal orifice plate;

During gas withdrawal, it exploits its inherent multiphase capability, providing not only the extracted gas flow but also a measurement for the free liquid.

An Innovative MPFM


| Slide 12


IS technology has proved to be perfectly fit to manage UGS metering needs.

Because of its unique design it is able to:

An Innovative MPFM


| Slide 13


First commercial installation of MPFM for UGS applications was performed in 2007 in Ripalta (Italy)

Goal: testing and validating the technology

The meter was installed downstream of the dehydration column to measure known minimal amounts (LVF ≈ 10-4 %) of TEG injected by a small pump into the dry gas

Field Results



First commercial installation of MPFM for UGS applications was performed in 2007 in Ripalta (Italy)

Goal: testing and validating the technology

Field Results



Tests were performed in very challenging and unfavorable conditions:

Because of logistics constraints the meter had to be installed in horizontal arrangement

A special meter configuration was designed and realized and specific compensation algorithms developed

Size (12”) was much larger than traditional MPFM

Field Results


Test

Ref. GasFlow

[KSm3/h]

MeterGas Flow

[KSm3/h]

Gas Flow Error[%]

Injected TEG[l/h]

LVF [%]

Meter Liquid Flow[l/h]

Liquid Flow Error[%]

1 188 185 -1.3 16 4.74E-04 14.5 -9.12 250 251 0.4 14 3.12E-04 15.2 8.63 250 249 -0.4 18 3.99E-04 19.7 9.44 250 252 0.8 20 4.51E-04 18.4 -8.25 83.3 84 0.8 10.5 7.42E-04 9.8 -7.06 83.3 83 -0.4 19 1.36E-03 21.3 12.17 170 173 1.8 34 1.16E-03 32.2 -5.3


The meter proved to be very effective in measuring both liquid and gas with good accuracy

A field calibration was required just to suppress the discrepancies due to peculiar geometric conditions

After proper meter calibration, liquid measurement error was reduced below 10%

Field Results



The results were up to the requirements, proving the effectiveness of the technology

IS-based MPFM were progressively installed at a few Italian UGS sites, replacing the orifice plate flowmeters between the well and the manifold and enabling gas treatment optimization

Standard vertically mounted meters allow for higher accuracy with no need for stratification compensation

VIS with its more compact and lighter footprint promises to ease installation and enhance ROI for UGS operators

Field Results



Measuring liquid entrained in gas during extraction from underground reservoir provides relevant benefits in UGS operations

Industry never focused on, due to the unavailability of solutions able to cover the challenging requirements

Isokinetic sampling based MPFM proved to be able to effectively detect liquid also at trace levels

The described application allowed to validate the technology in the most complex scenario

Following this application more than 25 MPFMs have been installed at Italian UGS fields to help operators improving reservoir management.

Conclusions


MPFM for Storage Gas Applications

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