Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
2002-12-03
2004-03-16
Neuder, William (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S053000, C166S372000
Reexamination Certificate
active
06705397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to producing wells having an artificial lift system for removing liquid from an underground formation. In one of its aspects, the invention relates to improved methods of and systems for control of artificial lift systems utilizing pressure measurements and pressure manipulation to detect the liquid level in the well bore to thereby increase the efficiency, operational predictability and to automate the artificial lift systems. In another of its aspects, the invention relates to the monitoring of production gas from a gas producing well and detection of the liquid level in the well bore to thereby control the artificial lift system to maximize gas production from the well while simultaneously maximizing artificial lift system performance and efficiency.
2. Description of Related Art
Artificial lift systems are commonly used to extract fluids, such as oil, water and natural gas, from underground geological formations. Oftentimes, the formations are more than 1,000 feet below the surface of the earth. The internal pressure of the geological formation is often insufficient to naturally raise commercial quantities of the liquid or gas from the formation through a bore hole. When the formation has a sufficient internal pressure to naturally lift the liquid from the formation, the natural pressure is often inadequate to produce the desired flow rate. Therefore, it is desirable to artificially lift the liquid from the formation by means of an artificial lift system.
Typically, the formation can comprise several separate layers containing the liquid and gas or can comprise a single large reservoir. A bore hole is drilled into the earth and passes through the different layers of the formation until the deepest layer is reached. Due to economic considerations, many bore holes extend only to the deepest part of the productive formation. In certain applications it is desired to extend the bore hole beyond the bottom of the productive formation. The portion of the bore hole that extends beyond the bottom of the formation and into the substrata is known as a “rat hole.” The location and depth of the bore hole is carefully controlled because of the great expense in drilling the bore hole.
After the bore hole is drilled, the bore hole is usually lined with a casing along its entire length to prevent collapse of the bore hole, to control reservoir pressure and to protect surface water from contamination. However, the bore hole is often only lined with the casing to the top of the gas and liquid containing formation, leaving the lower section of the bore hole uncased. The uncased section is referred to as an open hole. The casing is cemented in place and sealed at surface by a wellhead and can have one or more pipes, tubes or strings (metal rods) disposed therein and extending into the bore hole from the wellhead. One of the tubes is typically a production tube, which is used to carry liquid to the surface.
Currently, many different types of artificial lift systems are used to lift the liquid from the formation. The most common artificial lift systems are: progressive cavity pumps, beam pumps and subsurface gas lift (SSGL). A progressive cavity pump is relatively expensive, approximately $20,000 to install, but can deliver relatively large volumes of liquid and remove all the liquid from the formation. A progressive cavity pump can comprise an engine or electric motor driven hydraulic pump connected to a hydraulic motor mounted on the top of the wellhead and connected to a pump at the bottom of a production tube. The hydraulic motor turns a rod string that is connected to a pump rotor, which turns with respect to a pump stator. Alternately, some progressive cavity pumps are driven by an electric motor attached to the top of the well head. The pump rotor is helical in shape and forms a series of progressive cavities as it turns to lift or pump the liquid from the bottom of the well bore into the production tube and to the surface. Although the progressive cavity pump is satisfactory in raising liquid from the formation, the hydraulic pump system requires a containment building and liner in the event of an oil leak. The possibility of an oil leak in the progressive cavity pump system also raises environmental concerns because many of the bore holes are drilled in environmentally sensitive or wilderness areas. The progressive cavity pump also requires, in certain applications, at least 100 feet of a rat hole, which adds extra cost. Of the previously mentioned artificial lift systems, the progressive cavity pump has the highest maintenance costs and greatest amount of down time requiring rig service. This down time often results from a lack of good liquid level control which allows the well to be pumped off causing damage to the pump system. Also, a soft seal stuffing box which must be lubricated regularly is used to seal around the rotating rod string and acoustic annular liquid levels must be obtained at regular intervals to ensure that the liquid is adequately high above the pump so that it does not run dry and destroy itself.
A beam pump is also relatively expensive, approximately $18,000, to install but can also remove all the liquid from the formation. The beam pump comprises a pivotally mounted beam that is positioned over the wellhead and connected to a rod string extending into the production tube within the casing in the bore hole. The lower end of the rod string is connected to a pump disposed near the bottom of the well bore. The beam pump can be operated by a gas engine or an electric motor. The beam pump has several disadvantages. First, there are many environmental concerns. There may be leakage in the engine or gear box of the power source, requiring construction of a containment area. Further, if an electric motor is used in place of the gas engine, it is necessary to run a power line to the electric motor, which often destroys or degrades the surrounding environment. The beam pump, like the progressive cavity pump, has many moving components that require regular lubrication. The beam pump also uses a soft seal stuffing box to seal around the reciprocating rod string to contain liquids and gases produced up the production tube.
The SSGL is the least expensive artificial lift system to install, approximately $7,500. The SSGL uses pressurized gas carried by a separate tube, commonly referred to as a side string, from the surface to the lower end of the production tube to eject the liquid in the production tube to the surface upon injection of a blast of pressurized gas. The production tube usually has at its lower end a one-way valve called a “standing valve” which permits liquid standing in the formation to enter the production tube and rise in the production tube to the level of liquid in the formation. Often the SSGL system will have a plunger disposed within the production tube, but a plunger is an optional device to provide mechanical advantage for the blast of injection gas.
The SSGL is the most environmentally friendly, maintenance free and energy efficient of the three commonly used artificial lift systems. Unlike the other artificial lift systems, the subsurface gas lift system requires no systematic lubrication of the gas regulator and the motor valve. The SSGL maintains greater integrity of the well head in controlling the possibility of liquid leaks because the well head components are hard piped with no friction oriented soft seal such as is found in the stuffing boxes of the progressive cavity and beam pumps. The SSGL is virtually silent during operation and has very little surface equipment compared to a beam pump or progressive cavity pump. Therefore, it has less audible and visual impact on the surrounding environment.
The greatest disadvantage of the SSGL is that it becomes less efficient and more difficult to control as more and more liquid is removed from the formation. The SSGL can only raise the column of liquid in the production tube. The column of liquid in the production tube is equ
McGarry Bair PC
Neuder William
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