11/08/2026
Well Testing
Engineers analyze responses to pressure change schemes using pressure transient analysis, a technique based on the mathematical relationships between flow rate, pressure, and time. The information from these analyses helps engineers determine the optimal interval, production potential, and skin. They can also derive average permeability, degree of permeability heterogeneity and anisotropy, boundary shape and distance, and initial and average reservoir pressures.
Engineers use specific variations on well buildup and drawdown tests to evaluate gas wells. During a backpressure test, a well flows against specified backpressure until its BHP and surface pressures stabilizeโan indication that flow is coming from the outer reaches of the drainage area. An isochronal test is a series of drawdowns and buildups. Pumping rates vary for each drawdown, while subsequent buildups continue until the reaches its original shut-in pressure. A modified isochronal testโin which drawdown and buildup periods are of equal durationโmay also be used.
Based on data from these tests, are able to determine production potential, skin, and absolute open flow (AOF)โthe theoretical rate at which the well would flow if backpressure on the sand face, or the borehole wall, were zero. Operators use AOF as the basis for calculations to determine the relationship between backpressure settings and flow rates of the well.
Rather than use well tests, operators may opt to evaluate their wells using wireline formation testers that include a quartz pressure gauge and a fluid sampling tool placed across a production interval (Figure 2). During these tests, reservoir fluids are pumped or flowed into the wireline formation tester through a probe inserted into the formation or between packers set above and below the sampling site.
formation tester sampling. Pistons are driven from one side of the wireline formation tester to force a packer assembly firmly against the formation to be tested. At its center, the packer includes a probe that is then extended into the formation to withdraw fluids. Formation fluids (red arrows) flow into the probe and into flow lines. The fluids are pumped into the wellbore until they are sufficiently free of contamination as determined by downhole fluid analysis (green and brown cylinders). Uncontaminated fluids are directed into storage bottles (orange) where the fluids are kept in situ conditions. Multiple samples can be taken on one trip into the well. When all tests are completed, the samples are brought to the surface and may be sent to laboratories for advanced testing. A quartz pressure gauge measures and records bottom hole pressures.
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