Patent ID: 8794320
Filing Date: 2014-08-05
Classification: E21B

Abstract:
1. A system comprising: a well drilled into an underground formation comprising hydrocarbons; a production facility at a topside of the well; a water production facility connected to the production facility, the water production facility comprising a pressure driven first membrane system comprising a nanofiltration membrane designed to selectively reject a greater percentage of multivalent cations than monovalent cations from a water source containing multivalent cations and monovalent cations, and a pressure driven second membrane system located downstream of the first membrane system, the second membrane system comprising a reverse osmosis membrane designed to remove from 60% to 99% of cations from a water source; wherein the water production facility produces water by removing some multivalent cations from water containing multivalent cations and monovalent cations by passing the water through the first membrane system, by removing some monovalent cations from the water from which some multivalent cations have been removed by passing the water from which some multivalent cations have been removed through the second membrane system, and by adding back some multivalent cations to the water from which some of the monovalent cations have been removed, and then injects the produced water into the well.