Determining Friction Factors for Measuring Productivity of Gas Wells
- R.V. Smith (U.S. Bureau of Mines)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- March 1950
- Document Type
- Journal Paper
- 73 - 82
- 1950. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 4.6 Natural Gas, 5.2.1 Phase Behavior and PVT Measurements, 5.6.4 Drillstem/Well Testing
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The theoretical background for calculating friction factors for flow in gaswells by two methods is presented. The first method, requiring pressures,temperatures and specific volumes of the flowing fluids at various depths inthe well bore, shows how the mechanical-energy-balance equation for verticalflow may be graphically integrated over the actual path of the expansion of thefluid in the well. Thus, assumptions regarding the effective temperature andeffective compressibility of the fluid in the well are avoided. The secondmethod presents an equation derived on a basis of the assumptions that both thetemperature and the compressibility are fixed at constant effective valuesthroughout the flowing column of gas. The second method provides a convenientand practical means of calculating friction factors for gas wells and lendsitself readily to the problem of calculating subsurface pressures in a flowinggas well. The application of both methods to actual test data taken on aflowing gas well is illustrated in the paper.
As friction factors for the producing strings of flowing gas wells cannot bemeasured directly and must be calculated from flow-test data, study of themethods of arriving at friction factors is a necessary adjunct to understandingthe characteristics of flow in gas wells. There are two methods of calculatingfriction factors for gas wells; they differ from one another mainly in thetreatment of the path of expansion of the fluid in the well. In the flowingwell, the energy consumed in lifting the fluid from the bottom to the top ofthe well, overcoming the friction between the moving fluid and the pipe walls,and increasing the velocity of the fluid as it flows up the producing string issupplied by expansion of the flowing fluid. The available energy is determined,by the expansion of the fluid that follows a path determined by conditions oftemperature, compressibility and phase changes of the fluid during theexpansion. A means of evaluating the available energy in a flowing gas well anddetermining the proportion of the available energy used in lifting the gas,overcoming friction, and increasing the velocity of flow is developed in thisreport. Knowing how much energy is consumed in overcoming friction makes itpossible to calculate friction factors for given flow rates in given sizes ofpipes in wells.
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