Method and equipment for offshore oil production with primary gas separation and flow using the injection of high pressure gas

A method for offshore oil production with primary gas separation and flow, by the injection of high pressure gas, comprising the steps of:

• allowing fluids produced by an oil well to flow through a flow line from a wellhead to a subsea primary separator where a primary separation between a liquid phase and a gas phase takes place;
• separating out said liquid phase in a lower part of said subsea primary separator and also allowing it to accumulate in an outlet flow line and in first and second flow lines, so that liquid phase accumulates in the lengths of said outlet, first and second flow lines which are horizontal or have only a small gradient;
• and
• injecting high pressure gas along a gas injection line to cause a flow to a gathering center of the liquid phase which has accumulated in at least one of said outlet, first and second flow lines;
• wherein the injecting step comprises the following steps:
• opening a shut-off valve among first and second shut-off valves respectively located in first and second U-shaped pipe lengths which respectively connect the gas injection line to said first and second flow lines for a predetermined period when a back pressure exerted by the volumes of fluid accumulated in the outlet flow line and in the first and second flow lines begins to increase and to adversely affect production from the well, so as to allow a volume of pressurized gas to pass into said respective flow line;
• preventing the injected pressurized gas from exerting back pressure which affects the production of the well with a check valve fitted in said respective flow line close to the point of connection between said respective flow line and said respective U-shaped pipe length;
• flowing the liquid phase, which has accumulated in said respective flow line to the gathering center;
• closing of the shut-off valve among said first and second shut-off valves;
• and
• accumulating the liquid phase in the flow line among said first and second flow lines into which the pressurized gas was injected.

A method for offshore oil production with primary gas separation and flow, by the injection of pressurized gas, comprising the following steps:

• closing a first shut-off valve of a first U-shaped pipe length, which connects a flow line to a pressurized gas line;
• flowing fluids produced by a well through a wellhead flow line from a wellhead to a subsea primary separating vessel where primary separation between liquid and gas phases takes place;
• separating out the liquid phase in the bottom part of the subsea primary separating vessel;
• accumulating the liquid phase in the flow line, wherein as the liquid phase accumulates in the lengths of the flow line which are horizontal or have only a small gradient;
• injecting pressurized gas along said pressurized gas line to cause flow, to a gathering center, of the liquid phase which has accumulated in the flow line;
• wherein the injecting step further comprises the following steps:
• opening the first shut-off valve of the first U-shaped pipe length for a predetermined period when the back pressure exerted by the volume of fluid accumulated in the flow line begins to increase and to adversely affect production from the well, so as to allow a volume of pressurized gas to pass into the flow line;
• preventing the injected pressurized gas from exerting any back pressure which affects the production from the well with a check valve fitted in the flow line close to the point of connection between the flow line and the first U-shaped pipe length;
• promoting flow of the liquid phase which has accumulated in the flow line to a gathering center with the injected pressurized gas;
• closing of the first shut-off valve;
• and
• accumulating the liquid phase in the flow line into which the pressurized gas was injected.