Assembly and method for production of gas or gas and condensate/oil

1. An underwater placed assembly for production of gas, or gas and condensate/oil, from subsea, gaseous reservoir, wherein at least one production well is provided from the seabed to a production zone and at least one water injection well is provided from the seabed to an injection zone, wherein the assembly comprises:

a pressure increasing device connected to the outlet from the production well in order to increase the pressure in a production flow from the production well, and

a water turbine connected to and driving the pressure increasing device, said water turbine has an inlet for water, which is directly drawn from a location in the sea adjacent to the water turbine and said water has a high hydrostatic pressure caused by the pressure of the water column between the sea surface and the well level, and an outlet connected to the inlet of the water injection well, the water turbine driven by and withdrawing at least a part of the hydrostatic energy from the water thus delivered with a lower pressure to the water injection well, so that water thus delivered to the water injection well has a lower pressure than the hydrostatic pressure at the inlet of the water turbine.

2. The assembly according to claim 1 , wherein the production well and the water injection well are fluid paths in one and the same well.

3. The assembly according to claim 2 , wherein the fluid path for production is an annular space around an inner pipe, while the fluid path for injection is in the inner pipe.

4. The assembly according to claim 1 , wherein the pressure increasing device is provided on top of a wellhead.

5. The assembly according to claim 1 , wherein the pressure increasing device is a gas compressor.

6. The assembly according to claim 1 , wherein the pressure increasing device is a multiphase machine/pump.

7. The assembly according to claim 1 , wherein the pressure increasing device and the water turbine are provided on a common shaft.

8. The assembly according to claim 1 , wherein the pressure increasing device and the water turbine are placed on the seabed at the outlet from the production well.

9. The assembly according to claim 1 , wherein the pressure increasing device and the water turbine are provided in a recess in the seabed at the outlet from the production well.

10. A method for production of gas, or gas and condensate/oil, from a subsea gaseous reservoir,

where at least one production well is provided from the seabed to the production zone, and

at least one water injection well is provided from the seabed to an injection zone, utilizing the assembly according to claim 1 , wherein the method comprises:

increasing the pressure in a production flow from the production well by means of a pressure increasing device connected to the outlet from the production well, and

injecting water through the injection well to the injection zone in order to maintain the pressure in the reservoir, whereby a water turbine is connected to the inlet of the water injection well, said water turbine is connected to and driving the pressure increasing device, the water turbine has an inlet for water, which is directly drawn from a location in the sea adjacent to the water turbine and said water has a high hydrostatic pressure caused by the pressure of the water column between the sea surface and the well level, and an outlet connected to the inlet of the water injection well, the water turbine is driven by, and withdrawing at least part, of the hydrostatic energy from the water thus delivered with a lower pressure to the water injection well, so that the water thus delivered to the water injection well has a lower pressure than the hydrostatic pressure at the inlet of the water turbine.