Heavy oil is an important component of petroleum hydrocarbon energy. As the light oil reserves in offshore oil fields are increasingly reduced and oil and gas extraction technology continues to improve, the proportion of heavy oil extraction continues to increase.
In the process of crude oil extraction, continuous and real-time measurement of the volume flow or mass flow of each component in the oil well product is very important. It can help producers understand changes in formation oil and gas content and formation structure, thereby optimizing production and improving oil field recovery.
Comparative analysis of several single well measurement methods：
1. Multiphase flow meter measurement
Using a non-separating multiphase flowmeter to measure heavy oil can avoid the problem of low measurement accuracy caused by low separation efficiency and achieve online dynamic and real-time accurate measurement. Online multiphase flowmeters generally use a combination of two or more of the following measurement techniques: radioactive, acoustic or electronic signal correlation methods, as well as capacitance, microwave technology, V-cone differential pressure method, neutron detection pulse, gamma absorption, differential Pressure or volumetric flowmeter, etc.
2.Weighing measuring device
Since 2003, gravimetric metering devices have been used for online metering of heavy oil. This device eliminates measurement errors caused by false volumes caused by gas in the oil. At present, weighing metering devices are still widely used in Liaohe Oilfield, Shengli Oilfield and other places.
3. Foam crude oil oil and gas separator (improved metering separator)
Usually, the separator used for oil well production metering is composed of a collision primary separation head, a gas demister and other components. The internal components are simple and poorly targeted. They only rely on gravity to separate the three phases of oil, gas and water, and the separation efficiency is low. Low, especially not suitable for heavy oil. In order to adapt to heavy oil metering, in 2002, Shengli Design Institute transformed and innovated the internal structure of the traditional separator and developed a foamed crude oil and gas separator.
The device consists of a cyclone pre-separator, a liquid distribution pipe, a buffer plate, a bubble puller, a liquid flow stabilizing plate and a gas separation bag.
Conclusion and Suggestion
The characteristics of heavy oil make it difficult to separate by gravity through density differences. When traditional separators are used for separation, the separated liquid phase usually contains gas, making the flow meter inaccurate or even impossible to measure. In addition, the traditional separator has large volume, weight, and pressure loss and is not suitable for measuring heavy oil in offshore oil fields. Based on the research and analysis, the following suggestions are given for the selection of heavy oil measurement solutions for offshore oil fields:
1) Weighing metering devices are widely used in Liaohe Oilfield, Shengli Oilfield and other places, but this device has a large measurement error (20% to 40%) for foaming crude oil and crude oil containing large amounts of saturated steam. The internal components of this device are complex and there are many movable parts, which are easily damaged during frequent movements. Especially when used in offshore oil fields, the amount of subsequent maintenance will be large. In addition, when the crude oil contains less gas, the device will have difficulty in discharging oil at the pressure liquid level. Currently, this device has no application performance in offshore oil fields.
2) Multiphase flowmeter technology adopts the principle of Venturi + gamma ray, which does not require gas-liquid separation and has no clear requirements on the upper limit of viscosity. As long as the crude oil can flow in the flowmeter, it is more suitable for heavy oil measurement.
3) The measurement method using double separators and improved separators can be considered, but it needs to be jointly developed with the design unit, because it is a patented product and has few applications, and the application effect needs to be investigated. In particular, whether this type of device has difficulty in pressing the liquid level, whether it will cause blockage, and whether the double separator can successfully overcome the impact of heavy oil hanging on the wall need to be further considered.
4) In the process of offshore oil field development, especially in the development of marginal oil fields, the size of the platform space has a greater impact on development investment. Therefore, compact and simple devices should be used as much as possible. Therefore, in the selection process of heavy oil metering equipment, the comparison of equipment size cannot be ignored.
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