Heavy oil occupies a large proportion of oil and gas resources, so it has become a research hotspot to strengthen heavy oil exploitation and enhance oil recovery. However, heavy oil is different from conventional crude oil, mainly because of its high viscosity, which is difficult to be exploited by conventional methods, so some special technological measures are required.

Thermal oil recovery is the main technology of heavy oil recovery today. Conventional thermal oil recovery technology and its application Conventional thermal oil recovery methods include steam method and combustion oil layer.

The steam method mainly includes two methods: steam huff and puff and steam flooding. Steam is a kind of thermal energy. After being injected into the formation, it can greatly increase the temperature of the oil layer.

As the temperature of the oil layer increases, the following effects can be produced:

(1) The viscosity of the crude oil is greatly reduced, and the flow coefficient of the crude oil is increased.

(2) Reservoir rock and fluid volume expand, increasing elastic energy.

(3) In the process of steam flooding, steam distillation and solvent extraction are produced, and an enrichment zone of light fractions appears at the front of the steam zone, which plays the role of miscible displacement of oil phase.

(4) The relative permeability of the oil phase increases, the relative permeability of the water phase decreases, and the residual oil saturation decrease. In development practice, steam huff and puff and steam flooding are two organic processes of steam injection for oil recovery. Steam huff and puff create favorable reservoir displacement conditions for steam flooding.

Meanwhile, large heat injected by steam flooding will make the reservoir temperature widely improved, displacing oil between wells to producing wells. The crude oil recovery rate in the steam flooding stage is generally up to 20% to 30%. For the entire heavy oil reservoir, the planned conversion of steam huff and puff to steam flooding can skillfully avoid the inefficiency period of steam huff and puff and steam flooding, and maintain the stable production of heavy oil reservoirs.

The principle of burning the oil layer is to inject air, oxygen or oxygen-enriched gas into the well, and rely on spontaneous combustion or use the underground ignition device to ignite and burn, so that it reacts with the organic fuel (crude oil) in the oil reservoir, and uses the generated heat to recover the unburned heavy oil.

According to the direction of the combustion front and the flow of oxygen, it is divided into forward fire flooding and reverse fire flooding; Besides, according to whether water is injected during or after the combustion process, it is divided into dry fire flooding and wet fire flooding.

In recent years, with the development of horizontal well technology, the technology of combustion oil layer has shown a new development trend, that is, from conventional fire flooding to compound flooding. For example, the use of horizontal wells to carry out gravity-assisted combustion of oil, combined fire and steam flooding, etc., can improve oil recovery and economic benefits.


The thermal recovery technologies such as multi-heat fluid stimulation and steam stimulation are effective. However, two strings for injection and production are required, resulting in higher thermal recovery development costs. In view of this, through the research on the lifting optimization, pipe string design, downhole key tools design, wellhead special equipment design, and selection of the surface supporting technology, an injection-production integration process for heavy oil thermal recovery well in offshore oilfield has been formed, realizing a breakthrough of integrated injection-production heavy oil thermal recovery process for offshore oilfields from 0 to 1. The field test results show that the tools used in this technology have good temperature resistance.

The working cylinder has a good match with the mechanical safety valve with flexible opening. The working cylinder runs smoothly. The inner pump cylinder stinger seal pressure resistance is 20 MPa, which meets the technical requirements. The total cost of the integrated process is 60% lower than that of the current process, which helps to achieve large-scale thermal recovery development of offshore heavy oil fields.


At present, the thermal recovery wellhead devices used on site are mainly used for steam injection operations in heavy oil wells. After the steam injection operation is completed, the wells will be braised, and then blow out. After the pressure is reduced, the wellheads and insulation tubes (VIT) will be replaced and used to perform rod-based oil recovery. But it is low production efficiency and more operations.

Sanjack Company has developed an integrated injection-production wellhead device. Without replacing the wellhead device and insulated pipe (VIT), it can be directly converted to pumping operation after steam injection, realizing the integration of injection and production。


The wellhead structure is composed of casing head (1), tubing head (2), adapter flange (3), the main bore combined flat gate valve (6), side wing combined gate valve (5), and choke valve (4), double ram polished rod BOP(7), etc.

wellhead structure


Working principle: When in use, the insulated pipe (VIT), rod pump, sucker rod, and polished rod are successively run into the oil well, and then the injection and production wellhead device is installed, and then the position of the polished rod is adjusted, and the steam injection channel is opened, and the polished rod is clamped and fixed by the clamping gate and sealed by the sealing ram.

At this time, the normal steam injection operation can be carried out. When the steam injection, braising, and blowout operations are completed, adjust the polished rod to the pumping position and release the ram to proceed with oil production with rod pump, and rod pump mainly includes screw pump oil production and sucker rod pumping.


The structure of this research and development can realize that without replacing the wellhead device and the insulated pipe (VIT), it can be directly converted to the oil pumping operation after the steam injection and blowout operations, which realizes the integration of injection and production, greatly reduces the number of operations, and improves the injection and production effectiveness.