Data processing: measuring – calibrating – or testing – Testing system – Of mechanical system
Reexamination Certificate
2002-12-30
2004-10-19
Shah, Kamini (Department: 2863)
Data processing: measuring, calibrating, or testing
Testing system
Of mechanical system
C700S028000, C073S053010, C702S013000
Reexamination Certificate
active
06807501
ABSTRACT:
REFERENCE TO FEDERALLY SPONSORED RESEARCH
Not applicable
REFERENCE TO A COMPUTER PROGRAM LISTING APPENDIX
Not applicable
FIELD OF INVENTION
The invention disclosed relates to dynamic load-rate relationships for individual, as well as for multiple fluid control devices that operate as a fluid sub-system or larger fluid system, such as pressure sensitive gas-lift valves used in the production of hydrocarbons, and more specifically to methods that describe, compare, and contrast the dynamic loading characteristics of these devices to improve the operation of such fluid systems and to ensure that such fluid systems are appropriately designed.
BACKGROUND OF THE INVENTION
Approximately 10% of the daily world oil production is generated by pressure sensitive gas-lift valves in approximately 60,000 wells worldwide. Gas-lift valves are also used to unload fluids that accumulate in new and existing wells in order to start oil and gas wells flowing and to increase the production of oil and gas. In addition, gas-lift valves are used to assist in the disposal of waste fluids in fluid disposal wells.
Technology to produce fluid from wells by air-lift or gas-lift has been available to the petroleum industry for more than one hundred years. From the inception of air-lift or gas-lift valve use, testing and evaluating these valves has been a complex and costly process. Current Art describing gas-lift valve systems to produce hydrocarbons usually requires more than one gas-lift valve for a single well. Multiple gas-lift valves, for example, ten valves, may be needed to produce hydrocarbons from a specific underground formation. These fluid control devices deteriorate during their use as a result of many environmental and operating conditions into which the valves are placed.
U.S. Pat. No. 6,591,201 (Hyde) dated Aug. 7, 2003. Fluid Energy Pulse Test System [FEPTS] describes new equipment and methods to evaluate efficiently the performance of fluid control devices, such as gas-lift valves, by short duration energy pulses. The FEPTS technology describes test chambers and related fluid systems, and computer automated methods that can determine valve dynamic characteristics, including, opening pressure, closing pressure, flow rate, valve flutter, bellows characteristics, and leaking components. Patent application Ser. No. 10/259,970 (Hyde), Fluid Energy Pulse Test System—Transient, Ramp, Steady State [FEPTS—TRS] describes improvements to the FEPTS apparatus and methods to generate temperature-controlled and acoustically monitored transient, ramp, constant-steady-state, and periodic-steady-state test data by explosive regulation of fluid pressure and fluid flow rate for fluid control devices under test.
U.S. Pat. No. 6,591,201 and patent application Ser. No. 10/259,970 in their entirety, are incorporated herein by reference, and are referred to collectively as FEPTS. The Art described by these inventions teaches how to generate test data for fluid control devices such as individual gas-lift valves that are commonly described as tubing retrievable [TR] or wireline retrievable [WR] injection pressure operated gas-lift valves [IPO-GLVs] or production pressure operated gas-lift valves [PPO-GLVs]. The circular dimensions of pressure sensitive fluid control gas-lift valves of varying lengths are standardized by industry with outside diameters of 1.5875 centimeters (five-eighths inches), 2.54 centimeters (one inch), and 3.81 centimeters (one and one-half inches).
When a well is to be operated by gas-lift valve technology, each individual valve in a string of valves must be sized to pass a required amount of fluid through the valve. Gas-lift valve strings lift fluid in wells either intermittently or continuously, depending upon the fluid producing formation properties. Sizing a gas-lift valve includes determining a port size, opening pressure, closing pressure, fluid flow rate, and valve load rate. Each gas-lift valve is placed in a well to perform its function of assisting in the lift of the well's economic fluid.
With current Art, when each valve in a gas-lift valve string is sized to conform to a gas-lift valve lifting design scheme, the resulting system may function excellently, moderately, poorly, or not at all. Inadequate or sub-optimal operation is a result of the current inability to compare and contrast the operation of individual valves in a string of valves before they are placed into a well. It is common practice in the petroleum industry to over design gas-lift valve strings so that some fluid will flow. As much as 200% error in the design of lifting parameters can occur. Common practice and economics dictate that if a gas-lift well is flowing, gas-lift valve parameters are not changed even if the lifting program is substantially sub-optimal. The principal gas-lift valve parameter that specifies how a gas-lift valve will function to open, close, and pass fluid is called the valve load rate.
The load rate of a gas-lift valve is determined by procedures described in the American Petroleum Institute Recommended Practice for Testing Gas-Lift Valves, 1995 and API Recommended Practice 11V2, Second Edition, March 2001. A gas-lift valve is subjected to small changes in pressure as the distance of valve-stem travel is measured. Stem travel from fully closed to fully open is commonly in the range from zero to 0.254 centimeters (0.100 inches) or zero to 0.508 centimeters (0.200 inches). By changing pressure, a graph of valve-stem travel with respect to pressure can be generated. This graph commonly shows a linear characteristic with dimensions of kPa per centimeter (psig per inch). When valve-stem travel is measured by increasing then decreasing pressure, a hysteresis effect occurs. The increasing and decreasing pressure paths of valve-stem travel with respect to pressure are averaged to generate a numerical load rate, for example, 1397 kPa/centimeter (500 psig/inch).
The evaluation of a gas-lift valve load rate is time consuming, requires some valve disassembly and special equipment to monitor stem travel, and applies only to the specific gas-lift valve evaluated. The gas-lift valve load rate data are extrapolated to include all gas-lift valves manufactured to the same specification under various pressure conditions. Thus a benchmark criterion is generated to create a valve load rate.
A gas-lift valve's load rate is closely related to the valve's parameter settings for opening pressure, operating pressure, closing pressure, and fluid flow rate. When a gas-lift valve is configured for a gas-lift valve string, the common practice is to set the valve's bellows-dome pressure, the valve's-spring compression, or where applicable, a combination of dome pressure and spring compression. The load rate test is a static test and the petroleum industry has standardized load rate test criteria. For nitrogen charged valves, the nitrogen dome is charged to a pressure of 5617.1 kPa (800 psig), 8274 kPa (1200 psig) and in a separate test, to the manufacturer's maximum charge pressure. All pressures are referenced to 15.56 degrees Celsius (60 degrees Fahrenheit). For spring loaded valves, the spring compression is set to provide the manufacturer's maximum recommend set pressure. Specialized equipment requiring some valve disassembly is used to measure stem travel with a micrometer probe. Data are taken at different pressures and a load rate for the gas-lift valve is obtained by averaging the test results. A single numerical load rate value for a valve is generated in units of kPa per centimeter (psig per inch).
Each valve in a string, manufactured under the same specifications, is assumed to follow the load rate data generated by a benchmark load rate test. Gas-lift valve strings with multiple valves are then designed by selecting a gas-lift valve with a specific port size and setting each individual valve in a string to its design opening pressure. These static activities do not provide any information about how a gas-lift valve
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