Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
2001-01-24
2004-04-06
Suchfield, George (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S053000, C166S066000, C166S066700, C166S068500, C166S106000, C137S155000, C340S853300, C340S854400, C340S854500
Reexamination Certificate
active
06715550
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a gas-lift well having a controllable gas-lift valve, and in particular, to a controllable gas-lift valve which communicates with the surface and is powered using the tubing string and casing as the conductor.
2. Description of Related Art
Gas-lift wells have been in use since the 1800's and have proven particularly useful in increasing efficient rates of oil production where the reservoir natural lift is insufficient (see Brown, Connolizo and Robertson,
West Texas Oil Lifting Short Course
and H. W. Winkler,
Misunderstood or Overlooked Gas
-
lift Design and Equipment Considerations
, SPE, p. 351 (1994)). Typically, in a gas-lift oil well, natural gas produced in the oil field is compressed and injected in an annular space between the casing and tubing and is directed from the casing into the tubing to provide a “lift” to the tubing fluid column for production of oil out of the tubing. Although the tubing can be used for the injection of the lift-gas and the annular space used to produce the oil, this is rare in practice. Initially, the gas-lift wells simply injected the gas at the bottom of the tubing, but with deep wells this requires excessively high kick off pressures. Later, methods were devised to inject the gas into the tubing at various depths in the wells to avoid some of the problems associated with high kick off pressures (see U.S. Pat. No. 5,267,469).
The most common type of gas-lift well uses mechanical, bellows-type gas-lift valves attached to the tubing to regulate the flow of gas from the annular space into the tubing string (see U.S. Pat. Nos. 5,782,261 and 5,425,425). In a typical bellows-type gas-lift valve, the bellows is preset or pre-charged to a certain pressure such that the valve permits communication of gas out of the annular space and into the tubing at the pre-charged pressure. The pressure charge of each valve is selected by a well engineer depending upon the position of the valve in the well, the pressure head, the physical conditions of the well downhole, and a variety of other factors, some of which are assumed or unknown, or will change over the production life of the well.
Referring to
FIG. 1
in the drawings, a typical bellows-type gas-lift valve
310
has a pre-charge cylinder
312
, a metal bellows
314
, and entry ports
316
for communicating gas from the annular space outside the tubing string. Gas-lift valve
310
also includes a ball
318
that sealingly engages a valve seat
319
when valve
310
is in a closed position. When gas-lift valve
310
is in an open position, ball
318
no longer engages valve seat
319
, thereby allowing gas from the annular space to pass through entry port
316
, past ball
318
, and through exit port
320
. Several problems are common with bellows-type gas-lift valves. First, the bellows often loses its pre-charge, causing the valve to fail in the closed position or changing its setpoint to operate at other than the design goal, and exposure to overpressure causes similar problems. Another common failure is erosion around valve seat
319
and deterioration of the ball stem in the valve. This leads to partial failure of the valve or at least inefficient production. Because the gas flow through a gas-lift valve is often not continuous at a steady state, but rather exhibits a certain amount of hammer and chatter as ball
318
rapidly opens and closes, ball and valve seat degradation are common, leading to valve leakage. Failure or inefficient operation of bellows-type valves leads to corresponding inefficiencies in operation of a typical gas-lift well. In fact, it is estimated that well production is at least 5-15% less than optimum because of valve failure or operational inefficiencies. Fundamentally these difficulties are caused by the present inability to monitor, control, or prevent instabilities, since the valve characteristics are set at design time, and even without failure they cannot be easily changed after the valve is installed in the well.
Side-pocket mandrels coupled to the tubing string are known for receiving wireline insertable and retrievable gas-lift valves. Many gas-lift wells have gas-lift valves incorporated as an integral part of the tubing string, typically mounted to a pipe section. However, wireline replaceable side pocket mandrel type of gas-lift valves have many advantages and are quite commonly used (see U.S. Pat. Nos. 5,782,261 and 5,797,453). Gas-lift valves placed in a side pocket mandrel can be inserted and removed using a wireline and workover tool either in top or bottom entry. In lateral and horizontal boreholes, coiled tubing is used for insertion and removal of the gas-lift valves. It is common practice in oilfield production to shut off production of the well periodically and use a wireline to replace gas-lift valves. However, an operator often does not have a good estimate of which valves in the well have failed or degraded and need to be replaced.
It would, therefore, be a significant advantage if a system and method were devised which overcame the inefficiency of conventional bellows-type gas-lift valves. Several methods have been devised to place controllable valves downhole on the tubing string but all such known devices typically use an electrical cable or hydraulic line disposed along the tubing string to power and communicate with the gas-lift valves. It is, of course, highly undesirable and in practice difficult to use a cable along the tubing string either integral with the tubing string or spaced in the annulus between the tubing string and the casing because of the number of failure mechanisms present in such a system. The use of a cable presents difficulties for well operators while assembling and inserting the tubing string into a borehole. Additionally, the cable is subjected to corrosion and heavy wear due to movement of the tubing string within the borehole. An example of a downhole communication system using a cable is shown in PCT/EP97/01621.
U.S. Pat. No. 4,839,644 describes a method and system for wireless two-way communications in a cased borehole having a tubing string. However, this system describes a communication scheme for coupling electromagnetic energy in a transverse electric mode (TEM) using the annulus between the casing and the tubing. The system requires a toroidal antenna to launch or receive in a TEM mode, and the patent suggests an insulated wellhead. The inductive coupling of the system requires a substantially nonconductive fluid such as crude oil in the annulus between the casing and the tubing, and this oil must be of a higher density that brine so that leaked brine does not gather at the bottom of the annulus. This system does not speak to the issue of providing power to the downhole module. The invention described in U.S. Pat. No. 4,839,644 has not been widely adopted as a practical scheme for downhole two-way communication because it is expensive, has problems with brine leakage into the casing, and is difficult to use. Another system for downhole communication using mud pulse telemetry is described in U.S. Pat. Nos. 4,648,471 and 5,887,657. Although mud pulse telemetry can be successful at low data rates, it is of limited usefulness where high data rates are required or where it is undesirable to have complex, mud pulse telemetry equipment downhole. Other methods of communicating within a borehole are described in U.S. Pat. Nos. 4,468,665; 4,578,675; 4,739,325; 5,130,706; 5,467,083; 5,493,288; 5,574,374; 5,576,703; and 5,883,516.
It would, therefore, be a significant advance in the operation of gas-lift wells if an alternative to the conventional bellows type valve were provided, in particular, if the tubing string and the casing could be used as the communication and power conductors to control and operate a controllable gas-lift valve.
All references cited herein are incorporated by reference to the maximum extent allowable by law. To the extent a reference may not be fully incorporated herein, it is incorporated by ref
Burnett Robert Rex
Carl, Jr. Fred Gordon
Savage William Mountjoy
Vinegar Harold J.
Shell Oil Company
Suchfield George
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