Application of Multiphase Flow Meter in Tarim Oilfield

The reason why multiphase metering technology and application has become a hot topic pursued by oil-producing countries around the world in recent years is that it changes the traditional separator metering mode of oil wells, simplifies the surface production process of oil fields, greatly reduces the cost of capacity construction, facilitates operation management, and improves the level of automation.

The development and testing of multiphase flowmeters in Tarim began at the end of 1992. Before 1995, we achieved multiphase metering by measuring total flow and phase fraction. We went through three stages: turbine flowmeter/gamma ray, vortex flowmeter/gamma ray, and correlation method/gamma ray.

Since the end of 1995, we have focused on the research of multiphase metering by measuring the phase fraction and flow rate of each phase. After several years of field tests, the metering principle and method of measuring the flow rate of each phase by the gamma ray correlation method and the phase fraction by the gamma ray absorption method have been basically recognized. The flow meter has now been basically finalized and formed into a series of products.

In order to improve the metering accuracy, measurement range, reliability and stability of multiphase flowmeters, some improvements and enhancements have been made in hardware and software recently.

Metering principle and composition of MFM multiphase flowmeter

1 Phase fraction measurement—γ-ray absorption method

2 Flow velocity measurement—cross-correlation method

Cross-correlation velocity measurement is based on the measurement of statistical similarity between two random signals. When the fluid flows through the pipeline, the upstream and downstream sensors installed at a certain distance (L) along the axial direction of the pipeline pick up two random signals from the flowing non-uniform fluid at their respective measurement points. By measuring the cross-correlation time ti between them, the velocity vi of the fluid flow can be obtained. Discussions and proofs on the correlation values ​​can be found in mathematical works.

3 Structure and composition of the measurement system

A complete MFM multiphase metering device generally includes four parts: phase fraction measurement device; flow rate measurement device; temperature and pressure measurement device; data acquisition and processing system.

Application and field data

Since the end of 1992, we have cooperated with the scientific researchers of Lanzhou Haimo Company to conduct field tests and use in Lunnan, Yaha, Tazhong No. 4 and other oil fields in Tarim. A total of 20 sets of the first four generations of prototypes or products have been used to perform hundreds of three-phase non-separation metering on nearly 100 oil wells. There are still 13 sets in use now, and in 1997, we creatively integrated 3 sets of three-phase flow meters of different specifications and supporting systems on a skid, successfully developed a mobile three-phase non-separation metering device adapted to the desert environment, and achieved good economic benefits.

Compared with separate metering, the non-separate metering system has the following advantages: ① It can realize continuous, online automatic metering, avoiding errors caused by representative problems of metering and sampling time; ② It is easy to operate and manage, and can realize unattended metering, with low operation and maintenance costs; ③ It has no resistance and moving parts, and is safe and reliable; ④ It can output three-phase metering results and automatically print metering reports; ⑤ It is easy to install, reduces space occupation, and saves construction investment.

Before the country and the industry issued relevant multiphase flowmeter regulations, the common practice of domestic and foreign oil fields was to compare multiphase metering with traditional separation metering to obtain the relative accuracy and credibility of multiphase metering. No exception, our Tarim Oilfield has also done a lot of experiments and research in this regard, and conducted field comparison tests in desert oil fields and offshore platforms, and tested on two multiphase flow comparison devices at home and abroad.

1 On-site measurement data

From December 1997 to June 2000, during hundreds of meterings of 45 single wells in Lunnan Oilfield, the original metering separator in the metering room was used to conduct on-site comparisons with multiphase flowmeters. This included metering under the condition of changing the production of the same well by changing the nozzle, and also metering comparisons of different well conditions, different oil and gas production and water content. The data statistics of metering results within the metering range of the flowmeter design show that the data with liquid accuracy within ±10% (relative error), gas accuracy within ±15% (relative error), and water content accuracy within ±3% (absolute error) accounted for 80%. [page]

2 Offshore oil field comparison

From December 30, 1998 to January 6, 1999, a field comparison test of the MFM2050 multiphase flowmeter was carried out on the SZ36-1B platform of Bohai Oil Company using the separation metering device of the platform. This test measured 14 flow points and 42 sets of valid data, of which 81% of the liquid volume accuracy was within ±7%, 67% of the water content accuracy was within ±4%, and 95% of the gas volume accuracy was within ±15%, achieving relatively satisfactory results.

3 Domestic testing

Two tests were conducted on the Daqing multiphase flowmeter test and comparison device in January 1997 and April 1998. The first test lasted 37 days, with 72 flow points and 189 valid data. About 60% of the points met the gas-liquid design accuracy (gas ±15%, liquid ±10%). The second test lasted 10 days, with 15 flow points and 225 valid data. Only the multiphase water content instrument was tested in the second test. The results of the two tests were not ideal. After further research and improvement in recent years, the instrument level has been improved. Another test will be conducted recently to determine the final accuracy of the flowmeter.

4 Overseas testing

From July 7 to 14, 1999, the National Engineering Laboratory (NEL) of the United Kingdom conducted an independent third-party test and evaluation on the MFM2050 multiphase flowmeter. This was the first time that the laboratory evaluated a multiphase flowmeter from China. The test results and conclusions are as follows: the MFM2050 multiphase flowmeter has a total of 56 test points. For all four flow states in the vertical pipeline, including bubble flow, slug flow, annular flow and tumbling flow, the root mean square error of the liquid flow is ±8.5%, with a confidence level of 86%; the root mean square error of the gas flow is ±9.7%, with a confidence level of 73%; the root mean square error of the water content is ±2.4%, with a confidence level of 79%; the test results are consistent with the British National Engineering Laboratory's prediction of the current development level of multiphase metering technology.

Technical and economic indicators achieved

1 Design technical parameters of flow meter

Medium temperature: 20~80℃

Ambient temperature: -20~70℃

Ambient humidity: ≤95%

Working pressure: ≤16MPa

Power supply voltage: 220V±10%,50Hz

Power consumption: ≤270W

Radioactive source:Am241

Leakage dose: ≤5mSv/y

Measuring range: Maximum total flow rate under working conditions: 2500~10000m3/d; Water content: 0~100%; Gas content: 10%~95% Uncertainty: Liquid production (relative error): ±10%; Gas production (relative error): ±15%; Water content (absolute error): ±3%

2 Economic and technical indicators achieved

(1) The MFM multiphase flowmeter can be used to measure the oil, gas and water three-phase products of oil wells without separation.

(2) The entire device can adapt to the desert environment of Tarim and can still operate stably and reliably in a high temperature of 40°C (ambient temperature) and a sandstorm environment.

(3) The software is reasonably designed and easy to operate. There is no "freeze" or other adverse phenomena during operation and debugging. It can generate and print reports, and can realize unattended measurement.

(4) The maximum continuous working time is more than 30 hours (the metering system is manually shut down due to the completion of metering).

(5) The reliability of the metering system achieving the designed accuracy within the designed metering range is close to 80%.

(6) The investment of this multiphase metering device is 1/4 of that of a separator metering device of the same size, and the price of a single unit is 1/10~1/20 of similar foreign products.

Problems

(1) Adaptability.

(2) Measurement accuracy.

(3)Price.

(4) Verification.

(5) Supporting standards and regulations.

(6) Approval from reservoir and quality technical supervision departments.

While countries around the world are competing to develop and research oilfield multiphase flowmeters, our Tarim Oilfield has successfully developed a new generation of multiphase flowmeters after 8 years of hard work, cooperation with manufacturers, and a large number of field tests and indoor research. The flowmeter has a scientific measurement principle, reasonable structure, and convenient operation. It can adapt to desert and marine environments and has been put into practical use, achieving good economic benefits; within the design measurement range, nearly 80% of the data meets the design accuracy requirements, which can meet the production needs of multiphase flowmeters.