Eccentric-Vein Gas Separation

For decades producers have fought the problem of lost pump efficiency due to downhole gas interference. Downhole pumps can lose 20% to 100% of published efficiencies due to free gas problems. This is especially true when the pump is placed above the perforations. To correct this problem producers have tried a variety of remedies. Some of the remedies, such as knockers, spring-loaded balls and backpressure valves. do not directly attack the problem. Although these tools have proven to be helpful in pump operations they do not solve the root problem. Gas interference in reciprocating pumps causes lost production. premature pump failure. rod parts and excessive wear on surface equipment. Other types of lift equipment are also affected by gas interference. Progressive cavity pumps require liquid to lubricate and cool the polymer sealing materials. Free gas will greatly decrease the efficiency and life of these pumps. This is also true with submersibles as they require a constant flow of fluids for motor coolant. The most common downhole separator is made from materials found in pump yards. A joint of pipe is perforated and orange pealed on the bottom. This is attached to the seating nipple or lower barrel coupling and a dip tube is attached to the pump. Gas separation takes place between the dip tube and inside diameter of the perforated sub. This tool is often called a "Poor-Boy" gas separator (Fig 1 ), The Fluid efficiency of this separator is limited to about 50 BPD due to the limited space between the dip tube and outer case. Pressure differentials created by the upstroke of the pump add to the tools inefficiency. On the upstroke a pressure differential is created between the inside of the separator and tube casing annulus and fluids flow into the gas separator. Fluids surrounding the separator often contain 75% free gas. Considerable mamounts of gas are drawn into the separator and very little separation takes place due to the pressure differential. In a conventional "Poor-Boy", most of the fluid and gas flow occurs on the tip stroke and most of the gas discharge occurs on the domnstroke creating low efficiency.