How to avoid the replacement of wellhead equipment during thermal recovery of heavy oil？
Heavy oil thermal flooding refers to a more effective method for heavy oil oilfields to increase the temperature of the formation crude oil and reduce the viscosity of the crude oil, thereby increasing the mobility ratio of the formation oil and increasing the oil recovery factor.
Heavy Oil features
1. High content of colloidal asphaltenes and less light fractions. High viscosity and high relative density are the most important characteristics of heavy oil;
2. The content of heteroatoms such as sulfur, oxygen and nitrogen is high. For example: the sulfur content of heavy oil in the United States, Canada, and Venezuela is as high as 3% to 5%;
3. Heavy oil contains more rare metals, such as: Ni, V, Fe, Mo, etc.;
4. The paraffin content in heavy oil is generally low, but there are also very few “double high crude oils”;
5. In the same heavy oil reservoir, the properties of crude oil are often very different in different sections of the vertical oil layer and between wells on the plane; in the same oil field or oil area, the properties of crude oil are even more different.
6. Visco-temperature characteristics of heavy oil (the theoretical basis for thermal recovery of heavy oil);
7. Distillation characteristics of heavy oil (one of the mechanisms of steam flooding and fire flooding); when the temperature rises to the bubble point (the lowest temperature when crude oil begins to vaporize), the light components in the crude oil will be separated into gas phase and recombined. The fraction remains in the liquid phase;
8. Thermal cracking characteristics of heavy oil (more prominent in the process of burning oil layers than in the process of steam flooding); thermal cracking of heavy oil means that when the temperature rises to a certain extent, the heavy components in heavy oil will be cracked into coke and light components;
9. Thermal expansion characteristics of heavy oil;
According to the driving mode, heavy oil steam injection can be divided into two stages: steam huff and puff and steam flooding, which is a common practice abroad.
Steam huff and puff: The method is simple, and the economic risk is small. Each well can perform 5 to 8 cycles of huff and puff, and the oil recovery rate is as high as 3% to 8%, but the crude oil recovery rate is only 10% to 20%, and a large number of recoverable reserves are lost. . The effective heating radius of steam huff and puff is less than 30m. (analog result)
Steam Drive: High technology, high investment, high speed, high energy consumption, whether high profit or high level depends on the advanced reservoir geological conditions and process technology.
With the widespread application of heavy oil thermal recovery, the demand and role of thermal recovery wellheads have become increasingly prominent, and thermal recovery wellheads have become an important part of steam injection. In recent days, heavy oil production in oilfields is exploited by injecting high-temperature and high-pressure steam into the underground oil layer and simmering the well. However, the existing thermal production wellhead device does not have the function of sealing polished rods. It is used for high-temperature and high-pressure steam injection, simmering and venting by steam injection wellheads. Oil production wellheads are used for oil production at room temperature, and wellhead installations need to be replaced during the production process between steam injection and oil production, which not only increases operating costs but also consumes a lot of manpower and material resources.
In response to the above problems, Sanjack has developed a high-temperature and high-pressure thermal wellhead device that does not require the replacement of wellhead devices during high-temperature and high-pressure steam injection, simmering wells, venting and oil production.
The wellhead structure consists of a two-stage polished rod stuffing box (1), spool (2), steam injection and oil production pipeline (3), valve (4), polished rod seal BOP (5), tubing hanger (6), tubing head (7), valve (8), valve (9), tubing (10), casing head (11), casing head pipeline (12), valve (13), valve (14), etc.
A polished rod sealed BOP is installed on the spool body. The polished rod sealed BOP has two symmetrical main cores, and is a split structure. There is a groove under the main core, and resistant high-temperature seals inside the groove and high-temperature resistant seals are fixed on the core of the main body by screws through pressure blocks. The main core, high-temperature resistant seals, and pressure blocks are all provided with a semicircular hole that matches the polished rod. The right side of the spool is connected with steam injection and the production pipeline, the right side of the tubing head is connected to the tubing head pipeline, and the right side of the casing head is connected to the casing head pipeline.
When injecting steam, install a two-stage polished rod stuffing box, close the left valve of the spool, the left valve of the tubing head, the valve of the tubing head pipeline, and the valve of the casing head pipeline, open the polished rod BOP, and the steam will be injected, through pipelines, spool, tubing hangers, and tubing to enter the underground oil layer; when in braising wells, turn off the polished rod seal BOP, and perform braising well; when vent out, open the polished rod seal blowout preventer, valves on the steam injection and oil production pipeline, and the valves on tubing head pipeline, valves on the casing head pipeline, downhole crude oil is discharged through the steam injection production pipeline, the tubing head pipeline, and the casing head pipeline;
When oil production is in operation, close the left valve of the spool and the left valve of the tubing head, the valves on the tubing head pipeline, the valves on the casing head pipeline, open the polished rod seal BOP, the valves on the steam injection oil production pipeline, and the crude oil enters the oil pipeline through the tubing, the tubing hanger, the spool, and the steam injection production pipeline to complete the oil production operation; when replacing the seals of the two-stage polished rod stuffing box, close the polished rod BOP and the valves on the steam injection production pipeline to replace the seals.
The wellhead developed by Sanjack has a simple structure. There is no need to replace wellhead devices during steam injection, braising wells, blowout, and oil production, and it can effectively prevent blowout accidents.