Changes

==Procedure: estimating gas pressure gradient==

==Procedure: estimating gas pressure gradient==

Follow this procedure to estimate the gas pressure gradient of a gas reservoir or potential gas reservoir.

Follow this procedure to estimate the gas pressure gradient of a gas reservoir or potential gas reservoir.

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*  If data are available on gas composition and formation temperature go to step 2.  

*  If data are available on gas composition and formation temperature go to step 2.  

*  If no data on gas composition or formation temperature are available, estimate gas density from the average gas chart (Figure 5-11) and go to Step 6.

*  If no data on gas composition or formation temperature are available, estimate gas density from the average gas chart ([[:file:formation-fluid-pressure-and-its-application_fig5-11.png|Figure 4) and go to Step 6.

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| 2

| 2

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| 3

| 3

| Read pseudoreduced temperature and pressure from Figure 5-8.

| Read pseudoreduced temperature and pressure from [[:file:formation-fluid-pressure-and-its-application_fig5-8.png|Figure 1]].

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| 4

| 4

| If not already known, estimate compressibility factor, ''z'' , from Figure 5-9.

| If not already known, estimate compressibility factor, ''z'' , from [[:file:formation-fluid-pressure-and-its-application_fig5-9.png|Figure 2]].

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| 5

| 5

| Using information obtained from steps 2, 3, and 4, estimate gas density from Figure 5-10.

| Using information obtained from steps 2, 3, and 4, estimate gas density from [[:file:formation-fluid-pressure-and-its-application_fig5-10.png|Figure 3]].

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| 6

| 6

==Determining z==

==Determining z==

The gas compressibility factor, ''z'', for the gas reservoir of interest may already be known because it was measured. In this case, use that value. If ''z'' is not known, use the figure below to determine it from the pseudoreduced temperature and pressure determined from Figure 5-8. Figure 5-9 uses values determined for Figure 5-8.

The gas compressibility factor, ''z'', for the gas reservoir of interest may already be known because it was measured. In this case, use that value. If ''z'' is not known, use the figure below to determine it from the pseudoreduced temperature and pressure determined from Figure 5-8. Figure 5-9 uses values determined for [[:file:formation-fluid-pressure-and-its-application_fig5-8.png|Figure 1]]

 

[[file:formation-fluid-pressure-and-its-application_fig5-9.png|thumb|{{figure number|5-9}}.]]

==Determining subsurface gas density==

==Determining subsurface gas density==

We can determine gas density from the figure below, knowing reservoir pressure, reservoir temperature, gas compressibility factor, and apparent molecular weight.

We can determine gas density from the figure below, knowing reservoir pressure, reservoir temperature, gas compressibility factor, and apparent molecular weight.

==Average natural gas==

==Average natural gas==

==Estimating subsurface gas density==

==Estimating subsurface gas density==

We can estimate gas density from Figure 5-11. The chart assumes an average gas composition and was made using the following:

We can estimate gas density from [[:file:formation-fluid-pressure-and-its-application_fig5-11.png|Figure 4]]. The chart assumes an average gas composition and was made using the following:

* Formation temperature = [[temperature::80°F]] plus 0.8° per [[length::100 ft]] of depth

* Formation temperature = [[temperature::80°F]] plus 0.8° per [[length::100 ft]] of depth

* z = supercompressibility factor

* z = supercompressibility factor

* z₁ = original supercompressibility factor

* z₁ = original supercompressibility factor

==See also==

==See also==