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1、5.7 Analysis of Gas well Flow Tests-25.7 Analysis of Gas well Flow Tests-2Gas Flow Tests with Smoothly Changing Gas Flow Tests with Smoothly Changing RatesRatesIn many testing situations,a strictly constant producing rate is impractical or impossible to maintain.A more probable mode of operation is
2、production at a constant surface pressure,and if tubing friction effects are negligible,the BHP is also constant.Data obtained under these non-ideal test conditions can be analyzed accurately with a simple modification of the transient flow equation for constant-rate production.For slightly compress
3、ible liquidspFor constant flow ratepFor smoothly changing ratesFor compressible gas in which non-Darcy effects are important,we can use in terms of adjusted pressures:pFor constant flow ratepFor smoothly changing ratesOnce we have identified the semilog straight line indicative of the middle-time re
4、gion,k is estimated from the m of this line:Non Darcy effect neglected Or the value of D foundandExample 5.2-Analysis of a Variable Rate Gas Flow Test A gas well was produced at a constant BHP of 1000 psia.Known data are summarized below and in Table 5.4.Average gas and formation properties are eval
5、uated at the arithmetic average of the initial and BHFPs,assuming non-Darcy flow effects are negligilble.=2,825 psiaSolution:1.The first step is to prepare a plot of Using the adjusted initial and BHPs in Table 5.4,calculate the plotting functions assuming negligible non-Darcy flow effects(i.e.,D=0)
6、.For example,at t=4.8 hours,the plotting function is vs.logt.Similarly,plotting functions for each measured rate are summarized 2.47.844.88.347.28.629.68.7812.08.9014.49.0019.29.1521.69.2124.09.2728.89.3733.69.4538.49.5243.29.5848.09.6360.09.7272.09.8184.09.8896.0 9.93120.010.03132.010.08144.010.121
7、68.010.19192.010.25216.010.32 From type-curve analysis,we have identified the beginning of the middle-time region at approximately 30 hours.Therefore,the slope of the line drawn through data points after this time is m1.09 psi/cycle.2.The effective gas permeability is calculated with3.Next,calculate the skin factor.=0.13md=4.85.7 Gas Flow Tests with Smoothly Changing Rates（End)