Section 3 - Oil Metering and sampling

Question 1

What is the primary reason for Sampling of Oil?

Answer 1

To determine composition of export crude. This is particularly important in eg shared pipeline agreements prior to the point of sale.

Question 2

What is fiscal metering?

Answer 2

The metering and quantification of export crude for the purposes of taxation.

Question 3

Why is it important to compare onshore and offshore metering readings?

Answer 3

To ensure no loss of product has occurred. It’s also important to consider packing and unpacking. See packing slide.

Question 4

What is meant by the term packing and unpacking in relation to a crude oil pipeline?

Answer 4

Multi component liquids are slightly compressible. Increases and decreases in the overall pipeline pressure produces small changes in the volume of oil contained within the pipeline.

Question 5

Where is the sampling and metering system typically placed?

Answer 5

As late as possible in the oil handling sequence - downstream of any booster pump. This ensures no gas breakout due to the increased pressure forcing any gases toward their dew point.

Question 6

What is one of the main factors in considering where metering is carried out?

Answer 6

It’s important to ensure metering is completed at a location where no further processing of fluid occurs. Ensuring the metered fluid is as representative of the export fluid sampled.

Question 7

Why is it important to meter downstream of water removal?

Answer 7

At a water content of 1% or higher, serious discrepancies occur in meter accuracy, which conflicts with the objectives of metering and sampling.

Question 8

How does a DP meter convey flow rate?

Answer 8

The differential pressure is calculated and a volumetric flow rate can be extrapolated or referred in tables and graphs. Mass flow can be calculated if density is known.

Question 9

At what position should the HP and LP tappings of an orifice plate be positioned?

Answer 9

1 X Pipe Diameter Upstream

1/2 Pipe Diameter Downstream.

Question 10

What is the most common type of orifice plate?

Answer 10

The square edge orifice plate is the most common.

Question 11

Why is it important to specific upstream minimum lengths or use flow straightening vanes before metering elements?

Answer 11

To ensure laminar flow is achieved and eddies are eliminated, which could be caused by bends, restrictions, upstream equipment etc.

Question 12

What is the Vena Contracta?

Answer 12

This is the point at which fluid flow is at its highest and pressure at its lowest

Question 13

What are five factors which govern the Magnitude of differential pressure through an orifice plate?

Answer 13

Type of Fluid
Pipe Diameter
Orifice Diameter
Flow Rate
Inlet Pressure.

Question 14

How does a turbine meter work?

Answer 14

A turbine meter works by introducing a rotor into a straight flow section. Each segment of the rotor equates to a known fluid volume. As the rotor tip crosses a magnetic pick up, a pulse is generated. The pulse frequency can be used to calculate and establish a flow rate.

Question 15

What is the first reason for metering and sampling crude oil flow?

Answer 15

To measure the amount of hydrocarbons removed from a reservoir, allowing field production plans to be updated and revised.

Question 16

What other instrumentation may you mind in an Oil metering Stream?

Answer 16

Pressure Transmitter
Temperature Transmitter
On-Line Densitometer

Question 17

Why is it important to measure other physical characteristics of oil metering flow?

Answer 17

The pressure, temperature and density measurements of a fluid may change as the fluid is being metered. It is important to calculate these variables and factor them into the overall flow calculation for the stream.

Question 18

What is meant by the term Proving?

Answer 18

Proving is the proving of a metering device against an accurately calibrated proving meter

Question 19

What is proving?

Answer 19

Proving is the comparing of an indicated, recorded volume of oil passing through a meter - with the actual volume as measured by the prover loop.

Question 20

What is another name for the proving correction factor?

Answer 20

This is the meter factor, which is;

Prover Reading/Metered reading.

Question 21

What is he criteria for asserting a meter under test has been proven?

Answer 21

When a flow meter reading, including any correction factor, falls within 0.5% of the prover loop volume, for at least five consecutive runs.

Question 22

What is meant by sampling for metering?

Answer 22

Sampling for metering involves the use of an online density measuring system. The system continuously samples the fluid and passes the density results to the flow computer. Combined with pressure and temperature, as well as flow rate, to calculate mass flow.

Question 23

What is meant by Sampling for Analysis?

Answer 23

This is carried out by a second system, usually a sample grabber, which extracts samples at regular samples and collects them in a sample jar. This is then analysed in detail.

Question 24

What is a BS&W meter?

Answer 24

This is a base sediment and water system, used to ensure the water and solids content of the crude being metered is maintained below pre-determined limits - usually 1%.