Downhole fluid separator in a multilateral well

A multilateral well system comprising:

• a fluid separator to be positioned at a junction between a main bore and at least one lateral well of a multilateral well, wherein the fluid separator is configured to receive a formation fluid from a subsurface formation surrounding the main bore, wherein the fluid separator is configured to separate the formation fluid into production fluid and nonproduction fluid;
• a first pump to be positioned at the junction and configured to pump the nonproduction fluid to the at least one lateral well for injection of the nonproduction fluid into a subsurface formation surrounding the at least one lateral well;
• a first flow channel configured to be a conduit for delivery of the production fluid to a surface of the multilateral well;
• a second pump to be positioned in the first flow channel and further uphole relative to the junction, wherein the second pump is configured to pump the production fluid to the surface of the multilateral well;
• and
• a second flow channel configured to,
• deliver an injection of a surface fluid from the surface of the multilateral well into an injection zone downhole in the multilateral well;
• and
• deliver a sample of the nonproduction fluid to the surface of the multilateral well.

A method of separating a formation fluid downhole in a multilateral well, the method comprising:

• drawing the formation fluid in a fluid separator, wherein the fluid separator is located at a junction between a main bore and a lateral well;
• separating the formation fluid into a production fluid and a nonproduction fluid;
• drawing production fluid to a surface via a first flow channel;
• delivering, via a second flow channel, a surface fluid from a surface of the multilateral well downhole;
• and
• injecting the nonproduction fluid and the surface fluid into the lateral well and out into a formation surrounding the lateral well.