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 Measurement 1-2 July 2015
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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
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However, when the gas is withdrawn, it will be contaminated by water and liquid hydrocarbons which must be removed before being supplied back into the distribution grid
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Because the amount of liquid into the withdrawn gas is not known, the gas dehydration cannot be tailored to the actual need in order to guarantee operation compliance
MPFM for Gas Storage Applications
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The measurement of on-line free liquid in withdrawn gas would provide a number of benefits:
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
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
MPFM for Gas Storage ApplicationsAn Innovative MPFM
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.
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
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