Technical Discussion – Failure Mechanisms Introduction: This discussion of failure mechanisms is the result of observing CBM production related pump and motor failures from 1999 to the present. Experience includes both wellhead and shop failure analysis, pump and motor tear-downs, and shroud function and materials redesign. The current WellTamer design reflects what has been learned from over 1000 units sold in the Powder River Basin. The WellTamer is a fully field tested product, now redesigned to minimize its cost.

Failure Mechanisms: Upthrust: Upthrust is the most prevalent mode of submersible pump failure. Basically, once the check valves are removed from the string, the ESP used must have the capability handling upthrust. In pump design this typically takes the form of thrust bearings in the wet end of the pump. Upthrust is discussed fully in the upthrust section. Solids Jamming: If the open hole completion method has a drawback it is the continual production of fines at the face of the coal. Also, if the structural integrity of the coal is poor, the entire face of the open hole may subside into the hole trapping the pump/motor and any appliance installed. In this case the best bet is to install a screened liner. In many applications, however, the open hole is completely viable. The problem of continual fines production can be dealt with by providing a pump intake screen. However, if you provide a pump intake screen, you must provide a way to purge the screen once it packs off, and it will pack off. You cannot depend on the backflow through a multi stage submersible pump to purge an intake screen. The pump is a significant choke on the back flow and the pump and motor are not made to spin backwards. Lubrication on the Kingsbury bearing in the bottom of the motor is questionable as is friction within the pump stages. Additionally, backflow through the pump is not vigorous enough to purge a properly sized screen. The WellTamer incorporates two features that facilitate a rigorous back flush of the screen. First, the screen is a continuous slot, v-wire screen designed specifically minimize solids lodging in the screen and for easy back flushing. Secondly, the flush valve diverts the backflow around the pump thereby obtaining a very rigorous backflush (See animated graphic). The efficacy of the screen backflush has demonstrated itself to be very reliable. Gas and water logs verify that production decreases gradually as the screen packs off. After a backflush the production levels return to clean screen levels. The WellTamer is a viable alternative to the screened liner. Motor Cooling: It is the motor manufacturers recommendation that 4” ESP motors be provided with a cooling sleeve. This is due to the fact that the rated amperage of the motor is a function of the convective cooling on the outer motor jacket. In an open or lined hole there is not enough flow to adequately cool a 4” motor. Heat is the cause of most motor failures. Motors without a cooling sleeve will overheat and fail prematurely. The WellTamer is constructed to provide a cooling sleeve for the motor. Any motor can perform at its rated amperage for many years and for over 100,000 restarts with adequate cooling. Degassing: First, check valves are not installed in the string to eliminate gas-locking. Secondly, it is imperative to remove gas prior to the pump intake. The performance of ESP’s falls off dramatically if there is even a small percentage of gas in the water being pumped. For example, the presence of as little as 4% by volume of gas may reduce the lift capabilities by 50%. The WellTamer includes a counter-flow degassing section that insures separation of the gas and water. Lab and field tests demonstrate that a 6’ degasser section made up of a 4” schedule pipe and central 1 1/2” down-comer can degas flows up to 35 gpm.