Oil Wellhead and Christmas Tree Manufacturers and Suppliers

How to avoid the problem of wellhead lifting during the steam injection process of offshore thermal recovery wellhead？

Heavy oil recovery is a developing technology to extract heavy oil in industrial quantities. Heavy oil reserves are estimated at more than 6 trillion barrels, three times as much as conventional oil and gas.

Factors affecting the difficulty of producing reserves include permeability, porosity, depth, and pressure. The density and viscosity of the oil are the determining factors. Density and viscosity determine the extraction method.

The viscosity of oil varies with temperature, which determines the degree of difficulty of extraction. The temperature can be controlled to move the oil without using other techniques. Density is more important for refineries because it represents the yield after distillation. But there is no relationship that connects the two.

Reservoirs exist at different depths and temperatures. Although viscosity varies greatly with temperature, density is the criterion for field classification. Crude oil density is usually expressed in terms of the American Petroleum Institute (API) gravity degree, which is related to specific gravity. The lower the API density, the higher the oil density. The API gravity of liquid crude oil ranges from 4º for asphalt-rich tar to 70º for condensate. Heavy oil is divided into super-heavy oil and light oil. Their API gravity is between 10 and 20º.

Crude oil from source rocks has an API-specific gravity of between 30 and 40º. Crude oil becomes heavy after extensive degradation, trapping and devolatilization. When a reservoir is contaminated by bacteria through groundwater, it degrades through chemical and biological processes. Bacteria then break down some of the crude oil components into the heavier ones, making it more viscous. Water carries away the lower molecular weight hydrocarbons in solution form because they are more soluble. When crude oil is encased in inferior seals, the lighter molecules separate and escape, leaving behind heavier components through devolatilization.

Heavy oil is usually found in geologically young formations because they are shallow and less efficient at sealing, making it possible for them to form.

With the continuous exploitation of offshore oil, heavy oil recovery technology has been transferred from land oil fields to offshore oil fields, and offshore single-bore double-well wellheads have gradually become an important part of offshore oil production control equipment. The safety, reliability, and stable operation of single-bore dual-well wellheads are related to the safety, work efficiency, and profitability of field operators. In order to achieve smooth operation, it is particularly important to avoid the uplift of the wellhead due to casing expansion. At present, single-bore double-well oil production wellhead devices are mainly used in conventional oilfields’ single-bore and double-well oil production technology. The pilot test of the offshore single-bore and double-well heavy oil thermal recovery process has been completed. It is found that the offshore single-bore dual-well thermal production wellhead device in use has the following two problems: one is that the thermal expansion and extension of the casing occurs during the thermal steam injection process, and the wellhead rises; the second is that during the use of offshore single-bore dual-well thermal, the safety valve equipped with the Christmas tree part has no shear function. When an accident occurs during the oil well testing operation, causing a blowout and other accidents, if the safety valve cannot be cut during the closing process, it will bring Insecurity for the crude oil production on the offshore platform.

In response to the above problems, Sanjack Group has developed a new type of single-bore dual-well offshore thermal recovery wellhead device, which is especially suitable for offshore oilfield steam injection and thermal recovery technology. A certain amount of casing extension space is set in the tubing and casing heads. , And a safety valve with a shearing function is installed on the master combination valve, which solves the problem of wellhead lifting caused by thermal extension of the casing during steam injection, and also solves the safety problem in the process of oil well logging.

The new single-bore dual-well offshore thermal recovery wellhead consists of casing head (1), tubing head (2), master gate valve (3), master combination valve (6), choke valve (5), gate valve (7), as shown below

The working principle of the wellhead: It is composed of casing head, tubing head, master combination valve, master gate valve, choke valve, and gate valve. The casing head has a surface casing extension space L1=100~300mm, and there is a casing extension space L2=300~700mm in the tubing head. When steam is injected into the oil well, the surface casing extension is applied to the casing head extension space L1, and the technical casing extension is applied to the tubing head extension space L2, and thus the wellhead will not be lifted.

In addition, a safety valve with a shearing function is provided on the master combination valve. When performing oil well testing operations,  in case of a blowout or other accident in the oil well, the safety valve can be closed and the test operation wire can be cut to ensure the safe production of the offshore platform; because the casing head and tubing head contains the surface casing and the technical casing extension space L1 and L2, the overall height of the wellhead is increased, but the space of the offshore platform is limited. The utility model has designed a special master gate valve. The lower flange of the master gate valve is connected with the upper flange of the tubing head, and its diameter is the same as that of the upper flange of the tubing head. The upper flange of themaster gate valve is a studded structure, which is directly connected with the lower flange of the master combination valve. This avoids the use of adapter flange connecting the master gate valve and the tubing head and the adapter flange of the master valve is removed, so the overall height of the wellhead is reduced, and the restriction on the height of the wellhead by the offshore platform is met.

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