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→Multi-point tests
==Multi-point tests==
==Multi-point tests==
[[file:production-testing_fig2.png|thumb|{{figure number|2}}Multi-point test used to estimate absolute open flow potential.]]
Multi-point tests are typically used to establish gas well deliverability and absolute open flow potential; these tests may also be referred to as gas well deliverability tests, backpressure tests, or flow-after-flow tests<ref name=pt09r1 />. Multi-point tests typically require the measurement of gas flow rates and surface pressures at four stabilized flow conditions; surface shut-in pressure is also measured. Generally, an increasing flow rate sequence is preferred to a decreasing rate sequence.
Multi-point tests are typically used to establish gas well deliverability and absolute open flow potential; these tests may also be referred to as gas well deliverability tests, backpressure tests, or flow-after-flow tests<ref name=pt09r1 />. Multi-point tests typically require the measurement of gas flow rates and surface pressures at four stabilized flow conditions; surface shut-in pressure is also measured. Generally, an increasing flow rate sequence is preferred to a decreasing rate sequence.
The surface shut-in and flowing pressure measurements are converted to bottomhole conditions and a log-log plot of <math>\bar{p}^{2} - p_{\rm wf}^{2}</math> versus flow rate, ''q'', is generated (Figure 2). The four points define a straight line with a slope that is generally between 0.5 and 1.0. This straight line is extrapolated to determine gas flow rate at a point where the flowing bottomhole pressure is zero; this rate is referred to as the absolute open flow (AOF) potential of the well.
The surface shut-in and flowing pressure measurements are converted to bottomhole conditions and a log-log plot of <math>\bar{p}^{2} - p_{\rm wf}^{2}</math> versus flow rate, ''q'', is generated ([[:file:production-testing_fig2.png|Figure 2]]). The four points define a straight line with a slope that is generally between 0.5 and 1.0. This straight line is extrapolated to determine gas flow rate at a point where the flowing bottomhole pressure is zero; this rate is referred to as the absolute open flow (AOF) potential of the well.
Multi-point test data can also be used to estimate permeability using a variable rate flow test analysis<ref name=pt09r20>Odeh, A. S., Jones, L. G., 1965, Pressure drawdown analysis, variable-rate case, in Pressure Analysis Methods: Dallas, TX, American Institute of Mining, Metallurgical and Petroleum Engineers, Society of Petroleum Engineers Reprint Series No. 9, 256 p.</ref>. For gas wells, the data are plotted as
Multi-point test data can also be used to estimate permeability using a variable rate flow test analysis<ref name=pt09r20>Odeh, A. S., Jones, L. G., 1965, Pressure drawdown analysis, variable-rate case, in Pressure Analysis Methods: Dallas, TX, American Institute of Mining, Metallurgical and Petroleum Engineers, Society of Petroleum Engineers Reprint Series No. 9, 256 p.</ref>. For gas wells, the data are plotted as