There have been many different types and kinds of pump control system for downhole well use and methods of using them relating to the controlling of the reciprocating action of a piston pump by a motor.
Conventional pump control systems and motor-pump assemblies of the general type with which the present invention is concerned are employed for lifting oil well fluids from the bottom of a well to the ground surface. The conventional, prior known motor-pump assemblies generally include an electrically actuated motor interconnected between a downhole pump by a connecting rod and a control system at the surface of the well.
While such systems may have been successful in many applications, they have proven to be less than satisfactory when placed in commercial production wells which are of a marginal production value. In this regard, because the fluids produced within a well diminish with time it has proven difficult, if not impossible, to adjust the performance of the downhole motor-pump assembly in an effective manner to accommodate the changing well production conditions. Moreover, if a connection rod breaks or the downhole pump fails, the long connecting rod and pump must be removed mechanically from the well for repair and then mechanically lowered back down into the well. In this regard, many times during pumping operations, the piston rod damages the production tubing and thus necessitates its removal and replacement.
Therefore it would be highly desirable to have a new and improved pump control system and method of using it for lifting downhole oil well fluids to the ground surface that would substantially eliminate the problems associated with the prior art systems. More particularly, the system should not necessitate the use removal and replacement of long piston rods and should eliminate the danger of damaging the production tubing.
Another problem associated with conventional motor-pump assemblies with which the present invention is concerned has been the down time associated with wells whenever a pump fails. In this regard it is very time consuming and costly to remove the pump from the well for repair purposes.
One attempted solution addressed to the concerns of the prior art is disclosed in U.S. Pat. No. 4,350,478 which discloses a downhole linear motor-pump assembly which is lowered by a cable downhole into the well fluids. While such an approach attempted to address the concerns of low production wells it did not prove to be entirely satisfactory because the assembly was not entirely properly supported downhole for efficient pumping.
In this regard, to develop a sufficient pumping action a motor-pump assembly requires a fulcrum or adequate attachment to the surrounding structure, upon which to exert its driving force.
Therefore it would be highly desirable to have a motor-pump assembly that may be easily raised or lowered within the production tubing of a well and which can develop sufficient pumping action to lift well fluids at the bottom of the well to the well surface at an effective pumping rate.
Another problem associated with a downhole motor-pump assembly is the problem associated with controlling the linear direct current (d.c.) motor downhole. More particularly, the armature of a linear d.c. motor must be reciprocated in a up and down motion for driving the pump piston in an efficient and effective manner. Thus, the linear motor requires a set of discrete windings which must be sequentially activated to produce the desired driving force. In order to properly sequence and control the linear motion of the stator, motor control signals must be sent downhole over long distances along with the high voltage pulses necessary to drive the motor. Such combining of high and low voltage signals in a long cable, makes it difficult, if not impossible, to control the downhole motor from the ground surface due to signal interference or loss of the control signal due to the inherent resistance of such a long cable.
Therefore it would be highly desirable to have a new and improved pump motor control system and method of using it for controlling and adjusting the performance and pumping rate of a downhole linear motor in a reliable and cost effective manner. Also, such a motor control should be adjustable to compensate for pumping rates for a declining supply of fluids in a wall.
Yet another concern of the prior art with respect to well down time has been the need to send highly qualified technical personnel to the oil well field to test the operation and efficiency of each of the downhole motor-pump assemblies. In this regard, prior known monitoring arrangements have only monitored a few variables and thus specific identification of certain malfunctions has not been entirely possible. As a result, cost and extensive service calls are required to identify and replace faulty pumps and motors and oftentimes, repeated service calls may be required before an actual faulty device is located and repaired or replaced. Such an arrangement has been very costly.
Still another problem that has been a concern of the prior art has been the cost associated with repairing or replacing a downhole motor-pump assembly. In this regard, because the motor-pump assembly has been an integral unit, it has proven difficult, if not impossible to repair or replace only the motor in a cost effective and efficient manner.
Therefore it would be highly desirable to have a motor-pump assembly that would be an integral unit but yet that would lend itself to the repair or replacement of either the motor or the pump in the event either of these units fail.
Therefore, it would be highly desirable to have a new and improved control system for use with a downhole well pump and linear d.c. motor that could monitor the operation and efficiency of a downhole motor-pump assembly in a simple and cost effective manner.