CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application PCT/IB2016/001135 filed Jul. 22, 2016, which published as WO 2018/015777 on Jan. 25, 2018. These applications are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to a gas-liquid separator for separating a multiphase fluid stream containing hydrocarbons, comprising:an introduction duct, the introduction duct defining an introduction opening for receiving the multiphase fluid stream; anda static first separation stage extending along a longitudinal axis, connected with the introduction duct, the first separation stage comprising an outer wall, an inner wall and at least an inner baffle located between the outer wall and the inner wall, the inner baffle being configured to induce an helical movement of the multiphase fluid stream around the longitudinal axis to drive a liquid contained in the fluid stream onto the outer wall and a gas contained in the multiphase fluid stream onto the inner wall.

The multiphase fluid preferentially comprises various fluids including liquid and gaseous hydrocarbons and/or water.

Such a gas-liquid separator is in particular intended for use in a gas producing well, in order to improve the performances of the well.

More generally, the separator may also be applied to any gas-liquid separation occurring downhole, and/or potentially above the surface.

BACKGROUND

The production rate of a gas producing well is very often dependent on the quantity of liquid which is simultaneously produced in the well.

Indeed, a gas producing well may also produce water or liquid hydrocarbons simultaneously with the gas. The liquid is for example partly in the form of droplets which are conveyed to the surface along with the gas.

Conventionally, the liquid part of the multiphase fluid stream recovered at the surface is removed from the gas, before transporting or liquefying the gas.

In a gas producing well, at the beginning of the well production, the gas flow rate is usually sufficiently high to convey the liquids it contains towards the surface.

Nevertheless, after some production time, the gas flow rate decreases. This leads to an increase of pressure of the fluid column at the bottom of the well. Indeed, the liquids conveyed in the gas have a higher weight contribution in the gas column when the gas flow rate is smaller due to higher liquid hold-up in the fluid column.

The productivity of the well can be significantly affected. In some instances, below a critical gas flow rate, the liquid cannot any more be lifted by the gas. It then continuously accumulates in the fluid column, until the production eventually stops by well self-killing.

In case of such an accumulation of liquid in the fluid column, to alleviate a potential stop of the production, an artificial lift of the produced liquid is needed, which can be carried out through gas lift or through pumping. Such solutions increase the production costs.

In order to improve the vertical lift performance (VLP) of the well, and to shift its intersection with the inflow performance relationship (IPR) of the well toward higher production rates, WO 2009/097869 discloses a solution in which the free liquid contained in a gas stream is separated at the bottom of the well, in order to decrease the weight of the gas column.

Accordingly, WO 2009/097869 discloses a static extractor comprising a separation stage provided with a centrifugal separator. Above the outlet region of the separator, an upper stage delimiting elongated slots is provided to collect the residual liquid.

Such a separator may be efficient for a gas flow only containing small droplets of liquids. Nevertheless, in some wells, the production sometimes follows a slug regime, in which significant volumes of liquids are extracted in between pockets of gas.

If such a separator was used with a hydrocarbon stream containing a significant volume of liquid, the liquid extraction would be complicated by the fact that the separator tube section would be filled in with liquid, leading to an incomplete and difficult evacuation of the liquid in the upper stage.

The design of such a separator is therefore difficult to control, and is only suitable for very specific production situations.

SUMMARY

One aim of the invention is to provide a very efficient separator for a multiphase fluid which can be easily inserted into a well, without a complicated maintenance, and which nevertheless remains very efficient with various types of flow regimes of the multiphase fluid.

To this aim, the subject-matter of the invention is a gas-liquid separator of the above type, characterized in that:the outer wall or/and the inner wall delimit(s) at least a lateral orifice for evacuating a respective one of the liquid or of the gas separated along the inner baffle, the or each lateral orifice extending along the or each inner baffle and defining a lateral staged evacuation of the respective one of the liquid or of the gas in an evacuation canal along the respective one of the outer wall and of the inner wall.

The separator according to the invention may comprise one or more of the following features, taken solely, or according to any potential technical combination:the inner wall contains a liquid circulation conduit, able to evacuate the liquid collected in the first separation stage;the inner baffle continuously and helicoidally extends along the longitudinal axis of the first separation stage;in a cross section containing the longitudinal axis, the or each inner baffle comprises successive transverse regions inclined downwardly between an inner peripheral edge and an outer peripheral edge, at least an orifice being located between two successive transverse regions, above the inner peripheral edge or above the outer peripheral edge;the outer wall has at least a lateral orifice for evacuating the liquid separated along the inner baffle, the or each lateral orifice extending along the or each inner baffle and defining a lateral staged evacuation of the liquid in an liquid evacuation canal along the outer wall, the first separation stage having at least an upper gas evacuation opening located above the inner baffle;an external guiding wall, located around the outer wall facing the first separator, the liquid evacuation canal being defined between the external guiding wall and the outer wall;it comprises fins interposed between the external guiding wall and the outer wall below the first separation stage, the liquid evacuation canal emerging downwardly between the fins;it comprises a second separation stage, located in the liquid evacuation canal, below the first separation stage, the second separation stage comprising at least an outer baffle configured to induce an helical movement of the liquid to drive a residual gas contained in the liquid towards the introduction duct, the introduction duct advantageously defining a least a gas recycling passage, emerging in the introduction duct;the outer baffle is a continuous helical baffle connected to the outer wall, and wherein advantageously, in a cross section containing the longitudinal axis, the outer baffle defines successive transverse regions inclined downwardly towards the external wall;the inner wall delimits at least a lateral orifice for evacuating a gas separated along the inner baffle, the or each lateral orifice extending along the or each inner baffle and defining a lateral staged evacuation of the gas in a gas evacuation canal along the inner wall.

The invention also concerns a hydrocarbon extractor for a well extractor for a well, comprising a collection space for collecting a multiphase fluid stream extracted from a reservoir, a separator as defined above, the collection space being connected to the introduction duct and a liquid transportation conduit, to evacuate a liquid separated from the multiphase fluid stream.

The extractor according to the invention may comprise one or more of the following features, taken solely, or according to any potential technical combination:it comprises a pump, the inlet of the pump being connected to the separator, the liquid transportation conduit being connected to the outlet of the pump;the pump is located below the separator, the pump being able to be activated at least partially by a turbine driven by a gravitational circulation of the liquid circulating from the separator;the liquid transportation conduit extends through the introduction duct and through the first separation stage.

The invention also concerns a method for separating a multiphase fluid stream into a liquid and a gas comprising:providing a gas-liquid separator as defined above;feeding a multiphase fluid stream into the introduction duct to the first separation stage;circulating the multiphase fluid stream in the first separation stage, an helical movement of the multiphase fluid stream being induced along the or each inner baffle to drive the liquid contained in the hydrocarbon stream onto the outer wall, and to drive a gas contained in the multiphase fluid stream onto the inner wall;recovering a respective one of the liquid or of the gas separated along the inner baffle through the or each evacuation orifice at stages along the longitudinal axis;evacuating the one of the liquid or of the gas through the evacuation canal.

