Steam injection technology for heavy oil thermal recoveryControl valveThe basic requirement is that it should be able to have a larger pressure drop function at a small flow rate, and a small pressure drop can be obtained at a large flow rate.Existing steam flow control valves are difficult to effectively adjust the steam flow within the full stroke range, and there are problems such as vibration and erosion.On the basis of analyzing the structure, working principle and existing problems of high pressure differential flow control valves at home and abroad, a new type of high pressure differential labyrinth steam flow control valve was developed.When the opening percentage of the regulating valve changes from 0% to 100% (the stroke is constantly changing), the flow percentage rises from 0% to 100%; otherwise, it drops. The entire stroke is close to 100mm, which can be adjusted easily, and the low pressure difference is achieved. Flow rate.When the valve inlet p-in=9.4MPa and outlet p-out=3.2MPa, the measured valve noise is 70dB (ordinary control valve noise reaches above 84dB), which fundamentally reduces erosion and noise. 1. The basic requirements of steam injection for heavy oil thermal recovery on flow control valves
After the thermal exploitation of heavy oil enters the steam flooding exploitation, a relatively fixed steam injection pipe network, a typical flow of steam distribution and metering will be formed.Three crucial issues in the steam injection process for heavy oil development are steam distribution, metering and regulation.Reasonable steam control can realize scientific steam injection, improve the oil-steam ratio of thermal recovery and the recovery factor of crude oil, thereby obtaining satisfactory economic benefits.The thermal recovery of heavy oil has two stages: single well huff and puff and steam flooding.In the entire thermal recovery process of the entire block, except for the single well huff and puff at the initial stage, single well huff and puff and steam flooding are generally performed at the same time.Therefore, the steam distribution station must simultaneously distribute injections to the huff and puff wells and the steam drive wells.In the thermal production site of Karamay Oilfield in Xinjiang, the pressure of huff and puff wells is high (5-10MPa) and the steam injection flow is large (6-10t/h), while the steam injection pressure of steam drive wells is low (2-5MPa) and the steam injection flow is small ( 1.5～5t/h).That is to say, the pressure difference between the distributor and the steam injection wells is different, and the difference is 3MPa or more. A flow resistance link must be added between the distributor and the steam injection well to absorb the remaining pressure.Obviously, the flow regulating valve used here should be able to have a larger pressure drop function at a small flow rate, and a small pressure drop at a large flow rate.This is how the steam injection process for heavy oil thermal recoveryControl valveSpecial requirements.
2. Problems existing in the existing steam flow control valve and high pressure differential flow control valve
In the current thermal production process, in order to reduce the pressure, the used regulating valve works with a very small opening. The steam flow rate in the valve is high, and the adjustability is poor, and it is difficult to reach the predetermined flow value.In addition, one distributor corresponds to multiple steam injection wells, and adjusting the flow rate of one of the wells will affect the flow rate of other wells, which increases the difficulty of flow adjustment.The resistance piece of the JT65y250V high-pressure steam regulating globe valve jointly developed by Shengli Oilfield and Xi’an High Pressure Valve Factory is a piston through-hole regulating structure.Figure 1 shows the relationship curve between the flow percentage and the opening percentage drawn based on the thermal recovery field operating test data.It can be seen from the curve that when the opening is from 0% to 10%, the flow percentage exceeds 60%, the adjustment sensitivity is too large, and the valve handwheel moves, either the steam flow is too large or too small.However, the adjustment sensitivity is too low when the opening degree is above 10%, and there is no adjustment function in the range of 40% to 100% opening degree.Therefore, it is difficult to effectively adjust the steam flow rate in the full stroke range.At the same time, when the valve opening is small, the fluid in the valve reaches a critical flow rate, which causes serious problems such as vibration and erosion.
Researchers at Xi’an Jiaotong University designed the GYY high pressure differenceControl valve(Figure 2), high pressure drop has been achieved, and the flow regulation characteristics have been improved. However, the excessively high critical flow rate makes the erosion, vibration, noise and other problems more serious, and high-strength, wear-resistant materials have to be used.In this way, not only the cost of the valve is increased, but the rate of change of the flow rate with the stroke is still large, and the adjustment characteristics have not been significantly improved.In addition, the critical flow generally requires the ratio of inlet pressure to back pressure to be greater than 2, which limits its scope of application.For example, some thermal production steam injection wells require a pressure of 8-12 MPa or higher, while the maximum pressure at the outlet of the boiler is 18 MPa, and it is impossible to form a critical flow.In field applications, this kind of regulating valve cannot effectively realize flow regulation and pressure drop regulation in a wide range under high temperature and high pressure, and its flow regulation mainly depends on the channel area of the last stage.This adjustment method is not fundamentally different from ordinary valves, and it is still difficult to adjust the valve opening to ensure the expected flow rate.A common feature of existing high-pressure differential flow control valves is that high-pressure differential will inevitably lead to high flow rates, and high flow rates will bring serious problems such as vibration, erosion, and noise.How to solve these problems is an important research topic for scientific and technical personnel.