The present invention relates to a proces for integrated catching of liguid plugs and separation of oil, water and gas in a lined rock cavern, advantageously in the form of a tunnel, independently of the ground water level the process being characterized that the catching/separation is effected in a pressure container arranged in the rock cavern, the volume of the said container giving sufficient buffer volume and residence time for separation in a single stage and without strength restrictions of structural materials limiting the size of the container, as the pressure forces exerted from the interior of the container being transferred to the surrounding rock formations.

The invention comprises also an installation for carrying out of the said process, the installation being characterized thereby that is comprises a lined rock cavern, advantage¬ ously in the form of a tunnel, and wherein it is arranged a container having a concrete lining and which acts as an integrated liquid slug catcher/ separator, and having volume for sufficient buffer effect and residence time for separa¬ tion in a single stage, in combination with pipelines for supply in single phase or multiple phase and for effluent in gas phase and oil phase and optionally water phase after separation and optionally also for drainage of water.

Advantageously the pressure forces are transferred to the rock formation through a concrete lining arranged between an inner sealing membrane and the rock around the cavern.

Advantageously are oil, water and gas being supplied to the container through the supply pipeline in single phase or multiple phase separated into separate phase streams for being passed to processing or consumption.

Advantageously the container is delimited against the entrance part of the rock cavern by means of a pressure resistant concrete plug.

Advantageously the ground water pressure in the rock forma¬ tion is relieved by drainage means near to the concrete lining so that back pressure against the seating membrane is prevented during the construction period, inspection and maintenance when the liquid slug catcher/separator not being internally pressurized.

The rock cavern toward the entrance part is advantageously delimited by means of a pressure resistant concrete plug.

Advantageously an inner sealing membrane is arranged between the concrete lining and the concrete plug and the inner space of the container, the concrete parts serving as a form- giving element for the sealing membrane when this is pressed to contact with the concrete parts because of the inner overpressure.

Advantageously the supply pipeline and/or exit pipes are passed through the concrete plug and/or walls and/or ceiling of the container.

Advantageoulsy are valves arranged in the supply pipe and/or exiting pipes for pressure and flow control or shut-off.

Advantageously is usual equipment for flow directing and energy killing arranged in the container in the rock cavern, in the form of baffle plates and/or deflectors as well as sand trap.

Thus, the invention relates to liquid slug catching/ separation of oil, water and gas in connection with delivery from pipelines transporting a two phase flow (i.e. oil and gas transport in one and the same pipeline) or where the flow can be of two phase character.

For two phase transport of hydrocarbons in pipelines it is known that liquid pools which from time to time fill a

substantial portion of the flow cross sectional area, so called "slugs" or liquid slugs, will cause instabilities and operation disturbances in an otherwise steady oil-gas flow. The size of the liquid slug formed in the pipeline will vary with the composition of the transported medium, the transport velocity, physical factors as pressure and temperature as well as the transport lane. At the receiving end of the pipeline there is a need for devices for taking up and separate liquid and liquid slugs from the gasous components prior to sending liquid phases and gasous phases separately to processing/consumption.

For great diameter transport pipelines where the liquid slugs can reach very large sizes, it is previously known a technique for separating liquid from gas in great tubes liquid slug catchers formed as long slightly stoping tubes coupled in parallel. Gas and liquid are fed into the parallel tubes in the upstream end via a distribution manifold.

Gas and liquid are permitted to flow with a low velocity and large free contact area in the parallel tubes from which the gas is drawn off from the upper part of the tubes and liquid from the lower part of the tubes at the downstream end. Such installations built hitherto for two phase pipelines are often very large. Lengths of 200-300 meters with 6-8 parallel tubes of 1 meter diameter and wall thickness of more than 2 cm not being unusual. Total weight of equipment can exceed 1000 tons of steel. Operating pressures of 100 bar and more is usual. Dimension criteria are necessary buffer volume, residence time and penetration depth for gas bubbles in liquid. It is because of strength considerations prohibited to build liquid slug catchers equivalent with the liquid slug catcher described in the foregoing as a single free-standing pressure tank built of steel.

The present invention reduces the requirement for space, costs and maintenance and increases the safety for personel,

installation and sabotage compared with the corresponding factors for known technique.

The idea forming the basis of the invention is that the liquid slug catcher/separator is arranged in the form of and in at least one lined rock cavern, advantageously a tunnel, where the rock formation will take up the pressure forces, a lining of concrete will serve to transfer the inner pressure forces from an inner membrane sealing in the form of steel, metal or suitable polymer material. For preventing that the membrane sealing falling inwardly (collapsing) caused by possible ground water pressure during construction, inspec¬ tion and/or maintenance when the installation is internally without pressure, drainage possibility between concrete lining and rock and/or between membrane and concrete lining has been arranged.

The installation has been delimited against the entrance portion of the rock cavern by means of at least one concrete slug.

An installation according to the present invention will then comprise pipe connections for incoming two phase pipeline, exiting gas and liquid pipes, connection valves and instru¬ mentation devices and internal means for energy killing, flow directing and baffle plates and deflectors for effective separation of liquid and gas, as well as usual sand trap devices .

The invention is more detailedly illustrated with reference to the attached drawing which schematically shows an install¬ ation according to and for carrying out the invention, with at least one rock cavern 1, advantageously in the form of a rock tunnel. The tunnel has a concrete lining 2 serving for pressure transfer to the surrounding rock formation and is together with a concrete plug 4 serving to give form to the sealing membrane 3. The end wall of the container is made up

of a concrete plug 4. The installation is arranged for connections for incoming supply pipe 5, outgoing gas pipe 6, oil pipe 7 and water pipe 11 and usual devices for energy killing and flow directing in the form of baffle plates and deflectors as well as sand trap being indicated by 8. Drainage pipes for ground water pressure relief are indicated and also valve devices 10 for control of flow and pressure and optionally shut off.