JPS5847000B2 - Steam plant for offshore oil fields - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam plant for injecting steam into an oil field, which is one method for improving the crude oil recovery rate in an offshore oil field.

The steam injection method can be used to great effect especially in oil fields that produce highly viscous oil (usually API degree 22 or less).

Since oil field boilers for this purpose are used as a type of hot water boiler, once-through boilers have been in practical use for some time.

Furthermore, when the steam temperature is 300° C. or lower, the fluidity of crude oil can be sufficiently increased and oil extraction can be facilitated.

However, the biggest bottleneck with this method is securing boiler water supply, and the problem was how to economically secure a large amount of boiler water supply in offshore oil fields.

The present invention eliminates the above-mentioned bottlenecks in the steam injection method and provides a steam plant that enables maximum utilization of the steam injection method for offshore oil fields.

An embodiment of the present invention will be described below based on the drawings.

In FIG. 1, reference numeral 1 denotes an oil field boiler, which heats boiler feed water a supplied from a water tank 2 by a water feed pump 8 to produce superheated steam.

Natural gas or crude oil, which is extremely abundantly produced in ordinary oil fields, is used as the boiler fuel C and is burned in the burner 3.

As the boiler feed water a, produced water obtained by a water generator is used.

Reference numeral 4 denotes a steam desuperheater, in which superheated steam sent from the boiler 1 is cooled by seawater injected through a seawater injection pump 9, turned into wet saturated steam d, and then injected into the oil field 13.

On the other hand, the superheated steam from the boiler 1 drives the turbine 5 to operate the generator 6.

Exhaust steam e discharged from the turbine 5 is sent to the water generator 7 and used as heating steam.

Product water f manufactured from seawater sent through the seawater pump 10 in the water supply device 7 is sent to the water supply tank 2 by the transfer pump 11 and stored.

Further, the exhaust steam e of the turbine 5 is used as heating steam in the water supply device 7, is condensed, and is circulated to the boiler 1 again as boiler feed water a by the feed water pump 8.

Reference numeral 12 denotes an oil extraction pump, which is driven by the generator 6.

Next, its operation will be explained.

In the plant of the present invention, the steam injection process and the water supply and oil extraction process are selected by valve operation. First, steam injection into the oil field 13 is carried out for a certain period of time, for example, about 10 days, and then a nearby oil well or steam injection well is used. At the same time as extracting oil, the water generator 7 generates water for water supply to the boiler, and the system is operated by repeating these two processes.

FIG. 2 shows the steam injection process, in which water a supplied from the water supply tank 2 through the water supply pump 8 is converted into superheated steam in the boiler 1, and seawater is injected into the superheated steam in the steam desuperheater 4. As a result, the temperature of the steam is reduced, and the steam is injected into the oil field 13 as wet saturated steam d.

Figure 3 shows the water production and oil extraction process.
The oil is extracted by

At the same time, the superheated steam generated in the boiler 1 drives the turbine 5, which operates the generator 6 to obtain power for the oil extraction pump 12 and other pumps. The condensate is used as heating steam for the boiler 1, and the condensate is circulated and supplied to the boiler 1 again through the water supply pump 8.

Further, the produced water f obtained from the seawater supplied to the fresh water generator 7 through the seawater pump 10 is stored in the water supply tank 2 through the transfer pump 11.

Equipment 1 to 12 shown in Figure 1 are installed on the oil drilling platform, but if a large capacity water tank 2 is required, it may be better to float it on the sea instead of installing it on the platform. is good.

An example of thermal calculation results regarding the boiler 1 and the steam desuperheater 4 of the plant of the present invention is shown below. For example, natural gas is used as the fuel for the boiler 1, the efficiency of the boiler 1 is set to 90%, and the feed water temperature and seawater temperature are set at 20%, respectively. °C, the outlet steam condition is 70 ky/iG + 500 °C, and the injection well inlet (desuperheater outlet) steam condition is 70 k! 9/iG, 8
The total amount of steam injected with a dryness level of 0 (285°C) is 2.
This is the case when the speed is 2,800 kg/h.

From this, it can be seen that the required evaporation amount of the boiler and therefore the capacity of the water permeation device need only be 70 times the amount of steam injection.

Further, when steam injection is carried out for 10 days in the plant of the present invention, a water supply tank capacity of approximately 1.20 Or 11'' is required.

Furthermore, in the case of the plant of the present invention, the purpose is also to drive a turbine, and the boiler is of a type that always generates superheated steam, so the type of boiler does not need to be a once-through boiler.

Additionally, the turbine is a back pressure turbine, but since the steam is condensed within the freshwater generator, there is no need to provide a separate condenser for the process.

As described above, the present invention has the following advantages.

(1) Seawater is injected into the steam desuperheater to reduce the temperature of superheated steam, so seawater can be efficiently evaporated and a large amount of steam for oil field injection can be produced.

Furthermore, equipment such as boilers, turbines, and water pumps are not affected by seawater at all, so there is no need to take corrosion resistance into account, which is advantageous.

(2) Since the plant includes a water production system, steam can be injected into offshore oil fields where it is difficult to obtain boiler supply water.

(3) The boiler can always be operated with high efficiency during the steam injection process, water production, and oil extraction process, and there is no waste.

When operating the water supply system using the multi-stage flash method or the multiple effect method, the heating steam must be 3 kg/iGx saturated (143°
C) is sufficient.

In the water injection process, the turbine exhaust gas is supplied to the water injection system, so the boiler can be operated at the same load as in the steam injection process.

(4) There are conventional methods of treating seawater or oil field water (which has almost the same composition as seawater) and supplying it to boilers, but in this case, the water treatment equipment is extremely expensive (about the same price as the boiler), and it is not easy to operate. It was difficult to put it into practical use because of the high cost.

In the present invention, water produced by a freshwater generator is used as boiler water instead of seawater, so conventional boiler water treatment is sufficient, which is advantageous in that it can be simplified.

(5) The water produced by the water generator can be used for various purposes other than boiler supply water, as required by the platform.

[Brief explanation of the drawing]

FIG. 1 is an overall system diagram showing an embodiment of the present invention, FIG. 2 is a system diagram for the steam injection process, and FIG. 3 is a system diagram for the water production and oil extraction processes. 1...Oil field boiler, 2...Water tank, 4...Steam desuperheater, 5...Turbine, 7...Building water equipment.

Claims (1)

[Claims] 1. A boiler that generates superheated steam, a steam desuperheater that produces injection steam for oil fields by spraying seawater on the superheated steam to reduce its temperature, and a steam desuperheater that produces injected steam for oil fields by heating the exhaust steam of a turbine driven by the superheated steam. A steam plant for an offshore oil field, characterized by having a water supply device that secures boiler supply water from seawater by using it as steam.