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.
Thermal properties of heavy oil:
- Visco-temperature characteristics of heavy oil (the theoretical basis for thermal recovery of heavy oil);
- Distillation characteristics of heavy oil (one of the oil recovery 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 crude oil will be separated into gas phase. The heavy fraction remains in the liquid phase;
- 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;
- 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, the economic risk is small, and each well can perform 5-8 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 amount 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 reservoir geological conditions and the advanced process technology.
Oil (gas) wellhead device is an important equipment for oil and gas production, and its performance is related to whether oil and gas wells can produce safely and efficiently. The development of the petroleum industry constantly puts forward higher requirements on the reliability and controllability of wellhead devices and valves, which prompts and promotes the continuous improvement and development of wellhead devices. As far as the overall wellhead device is concerned, its improvement mainly focuses on the reduction of size and weight, that is, lightness and flexibility; from the perspective of structure type, it mainly focuses on the improvement and development of gate valves, and vigorously promotes the use of parallel gate valves, and carry out product reliability analysis research.
The casing head is connected to the upper end of the casing string and consists of a casing hanger, a spool, a valve, etc. It is used to support the lower casing string and seal the annular space between the upper and lower casing layers. Oil Layer Casing is suspended by the casing hanger. The device bears the weight of the suspended casing string [1].
⑴Position: The casing head is located at the lower end of the wellhead device and is a component that connects the casing and various wellhead devices.
(2) Composition: The casing head is composed of the body, the casing hanger and the sealing component.
(3) Function: It is used to support the gravity of technical casing and oil layer casing, seal the annular space between each layer of casing, and provide transition connection for the installation of upper wellhead devices such as blowout preventer, tubing head and Christmas tree.
⑷The surface casing is connected with the lower flange of the casing head with the flange, and the oil casing is connected with the inner thread of the casing head with the thread.
The casing head is an important part of the heavy oil thermal recovery wellhead, and its performance directly affects the production efficiency and safety. At present, the casing head seals of high-temperature and high-pressure thermal recovery wells in various oil fields adopts rubber parts or graphite materials. The rubber parts are difficult to withstand high temperatures. Graphite has good high-temperature resistance but is easy to break, which easily causes the casing head seal to fail.
Therefore, Sanjack Company designed and developed an inner and outer tapered metal sealing casing head, which is resistant to high temperature, not fragile, stable in structure, and reliable in sealing. It can fully meet the requirements of casing sealing conditions in high temperature and high-pressure thermal recovery wells.
The casing head consists of casing head housing (3), gasket ring (5), tiedown screw (6), support seat (7), metal seal (8), retaining ring (9), adapter flange (10) , etc.
Working principle: The metal seal is composed of an inner ring and an outer ring. The outer diameter of the inner ring is processed into an outer cone, the inner diameter of the inner ring is processed with an inner groove and an inner lip, and the inner diameter of the outer ring is processed into an inner cone, and the outer diameter of the outer ring is processed into an outer groove and an outer lip. The outer cone of the inner ring matches the inner cone of the outer ring. The metal seal is installed in the hole of the adapter flange. The inner lip of the inner ring matches the casing. The outer lip of outer ring is matched with the inner hole of the adapter flange; by tightening the tiedown screw on the adapter flange, the inner lip and outer lip of the metal seal can be stimulated to fit closely with the outer diameter of the casing and the inner hole of the adapter flange, respectively ,to achieve the role of sealing，
The structural seal is made of metal material, which can withstand high temperature and is not easy to be damaged. It effectively solves the problems that rubber parts are difficult to withstand high temperature and graphite is easily broken, and ensures the reliability of casing sealing.。
