McKetta-Wehe Chart

In 1958, McKetta and Wehe published a chart for estimating the water content of sweet natural gas. This chart has been modified slightly over the years and has been reproduced in many publications, most notably the GPSA Engineering Data Book. A version of this chart is appended to this chapter. 

The McKetta-Wehe chart is quite accurate for all gases (sweet, sour, and acid) for pressure up to about 1400 kPa (200 psia). However, it is not applicable to sour gas at high pressure. Fortunately, most 

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To use this method, one finds the water content of sweet gas, typically from the McKetta-Wehe chart. Then the corrections for the acid gases are obtained from their respective charts. 

F - correction factor, unitless wM w - water content of sweet gas from the McKetta-Wehe chart, g/Sm3 or lb/MMCF... 

A typical chart for water content from this period is presented in Figure 4.21. In Figure 4.21 the water content chart at temperatures above the hydrate stability conditions is based primarily on the data of Olds et al. (1942) while the data of Skinner (1948) were the basis for extrapolations to temperatures below the hydrate formation point. A summary chart is given by McKetta and Wehe (1958). However, below the initial hydrate formation conditions, Figure 4.21 represents metastable values, as observed in gas field data by Records and Seely (1951). Kobayashi and Katz (1955) indicated that such concentration extrapolations across hydrate phase boundaries yield severe errors. 

The quantity of water in saturated natural gas at various pressures can be estimated from Figure 11-1, which is based on the correlation of McKetta and Wehe (1958). This chart provides essentially the same data as the frequently used correlation of McCarthy et al. (1950), but has the advantage of including corrections for gas specific gravity and water salinity. The corrections are used as simple multipliers for water content values shown on the main chart. For example, if the gas has a molecular weight of 26 and is in equilibrium with an aqueous phase containing 3% salt, the correction factors would be Cq = 0.98 and C = 0.93. For this case, and conditions of I50°F and 3.000 psia, the gas would have a water content of (0.93)(0.98KI04) = 95 Ih/MMscf. 

It is essential to estimate correctly the saturated water content in the incoming natural gas (generally expressed in mg/Sm ). This can be estimated by using simulation software or it can be calculated using equation of states. The most commonly used method to estimate the saturated water content is to use a saturated water content chart developed by McKetta and Wehe as presented in Figure 5.6 [3]. 

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