In producing oil from both natural and artificial water driven oil reservoirs, the wells ultimately produce sufficiently large volumes of connate water to constitute a serious operating problem and eventually production of the water forces abandonment of the well. The cost of raising water to the earth's surface and of separating it from the oil represents an economic loss and, in addition, in many instances, there is a problem in disposal of the waste water. Even more importantly, the total volume of fluid that can be produced daily is often limited by the well bore and artificial lift equipment so that water production unnecessarily reduces the oil production rate. In many instances, a portion of the reservoir is producing essentially all water, while the remainder is producing a substantial quantity of oil. If production from the watered-out portion of the reservoir is eliminated or reduced, the production, handling and disposal of large volumes of water is avoided. Certain polymers can reduce the water:oil production ratio so more oil is produced while handling less water. This results in major savings in operating costs, the avoidance of unnecessary depletion of the water drive, and increased production from the remaining oil interval which results in greater ultimate recovery and greater current income.
U.S. Pat. No. 4,330,450 is directed to amphoteric water-in-oil self-inverting polymer emulsions containing 1 to 35 pbw anionic monomer in the polymer. The primary use disclosed is in papermaking. Their use in secondary and tertiary oil recovery is suggested. However, polymers containing 1 to 35 pbw of anionic monomer were found to be poor polymers to enhance oil recovery.
USPTO Backgrounds
USPTO Backgrounds