Changes

===Sampling===

===Sampling===

A truly representative sample can best be obtained from the flow line. Another sampling method is by drill stem tests, although this water is usually contaminated with filtrate from the drilling mud. (For more details, see [[Drill stem testing]].) Additional sampling methods include formation testers such as the formation interval tester (FIT) and the repeat formation tester (RFT), which due to their ability to hold a limited volume, usually recover only filtrate. (For more on formation testers, see [[Wireline formation testers]].)

A truly representative sample can best be obtained from the flow line. Another sampling method is by drill stem tests, although this water is usually contaminated with filtrate from the drilling mud. (For more details, see [[Drill stem testing]].) Additional sampling methods include [[Wireline formation testers|formation testers]] such as the formation interval tester (FIT) and the repeat formation tester (RFT), which due to their ability to hold a limited volume, usually recover only filtrate. (For more on formation testers, see [[Wireline formation testers]].)

 

===Analytical methods===

===Analytical methods===

 

[[file:oilfield-water-analysis_fig2.png|thumb|{{figure number|2}}Stiff<ref name=pt05r149 /> diagrams used to show water compositions on maps.]]

oilfield-water-analysis_fig1.png|{{figure number|1}}Triangular plot showing relative amounts of cations in typical oil field brines. Relative amount of sodium changes, but calcium is always about five times magnesium. (After Dickey.<ref name=pt05r46>Dickey, P. A., 1966, [http://archives.datapages.com/data/bulletns/1965-67/data/pg/0050/0011/2450/2472.htm Patterns of chemical composition of deep subsurface waters: AAPG Bulletin], v. 50, p. 2472–2478.</ref>)

file:oilfield-water-analysis_fig2.png|{{figure number|2}}Stiff<ref name=pt05r149 /> diagrams used to show water compositions on maps.

In the past, only the six principal elements were reported. Only five of these were determined by analysis: calcium, magnesium, chloride, alkalinity (usually reported as bicarbonate), and sulfate. Sodium was estimated by difference. Results were reported as parts per million (ppm), but because the methods are volumetric, it is more correct to report those results as milligrams per liter (mg/L). Recently, physical methods such as atomic absorption and spectrometry have made it possible to analyze for the less abundant elements.<ref name=pt05r10>American Society for Testing Materials, 1990, Water and environmental technology: ASTM, v. 11., 01, 612 p., and v. 11., 02, 878 p.</ref> Some elements, such as barium, are important because they precipitate and plug pores. Others such as iodine and bromine may be economically profitable to recover. (For more on properties of reservoir water, see [[Petroleum reservoir fluid properties]].)

In the past, only the six principal elements were reported. Only five of these were determined by analysis: calcium, magnesium, chloride, alkalinity (usually reported as bicarbonate), and sulfate. Sodium was estimated by difference. Results were reported as parts per million (ppm), but because the methods are volumetric, it is more correct to report those results as milligrams per liter (mg/L). Recently, physical methods such as atomic absorption and spectrometry have made it possible to analyze for the less abundant elements.<ref name=pt05r10>American Society for Testing Materials, 1990, Water and environmental technology: ASTM, v. 11., 01, 612 p., and v. 11., 02, 878 p.</ref> Some elements, such as barium, are important because they precipitate and plug pores. Others such as iodine and bromine may be economically profitable to recover. (For more on properties of reservoir water, see [[Petroleum reservoir fluid properties]].)

|+ {{table number|1}}Example calculations to convert milligrams per liter to milliequivalents and milliequivalent percent

|+ {{table number|1}}Example calculations to convert milligrams per liter to milliequivalents and milliequivalent percent

|-

|-

! Element

! rowspan = 2 | Element || rowspan = 2 |  Factor || colspan= 3 | Water 1 || colspan = 3 | Water 2 

! Factor

! Water 1 – meq

! Water 1 – meq%

|-

|-

| Na⁺

! mg/L || meq || meq % || mg/L || meq || meq %

| 0.0435

| 44,100

| 1918

| 74

| 3040

| 132.2

| 99

|-

|-

| Ca²⁺

| Na⁺ || 0.0435 || 44,100 || 1918 || 74 || 3040 || 132.2 || 99

| 0.0499

| 11,000

| 549

| 20

| 21

| 1.0

| 0.5

|-

|-

| Mg²⁺

| Ca²⁺ || 0.0499 || 11,000 || 549 || 20 || 21 || 1.0 || 0.5

| 0.0823

| 1,500

| 123

| 6

| 7

| 0.6

| 0.5

|-

|-

| Total cations

| Mg²⁺ || 0.0823 || 1,500 || 123 || 6 || 7 || 0.6 || 0.5

|

 

| '''Total cations''' || colspan = 2 | || '''2590''' || '''100''' ||  || '''133.8''' || '''100'''

|

 

| 2590

| 100

|

 

| 133.8

| 100

|-

|-

| Cl^–

| Cl^– || 0.0282 || 91,800 || 2589 || 100 || 3240 || 91.4 || 70

| 0.0282

| 91,800

| 2589

| 100

| 3240

| 91.4

| 70

|-

|-

| SO₄^2–

| SO₄^2– || 0.0208 || None || — || — || 407 || 8.5 || 6.5

| 0.0208

| None

| —

| —

| 407

| 8.5

| 6.5

|-

|-

| HCO₃^–

| HCO₃^– || 0.0164 || 34 || 0.5 || — || 1870 || 30.7 || 23.5

| 0.0164

| 34

| 0.5

| —

| 1870

| 30.7

| 23.5

|-

|-

| Total anions

| '''Total anions''' || colspan = 2 | || '''2590''' || '''100''' || || '''130.6''' || '''100.0'''

|

 

|

 

| 2590

| 100

|

 

| 130.6

| 100.0

|}

|}

When a well starts to make water, it is necessary to find out where the water is coming from to determine what actions, if any, are needed. Another important reason for sampling and analyzing water is to determine its resistivity (''R''_w). This value is needed to determine its saturation (''S''_w) in the producing formation by wireline log analysis. Consequently, some well logging societies have compiled ''R''_w values for different regions.

When a well starts to make water, it is necessary to find out where the water is coming from to determine what actions, if any, are needed. Another important reason for sampling and analyzing water is to determine its resistivity (''R''_w). This value is needed to determine its saturation (''S''_w) in the producing formation by wireline log analysis. Consequently, some well logging societies have compiled ''R''_w values for different regions.

Water from dry holes is sometimes analyzed for traces of hydrocarbon-related organic compounds, such as organic acids and benzene. If they are found, it suggests that the formation had an oil accumulation in the vicinity.<ref name=pt05r175>Zarella, W. M. 1967, Analysis and significance of hydrocarbons in subsurface brines: Geochimica et Cosmochimica Acta, n. 13, p. 1155–1166., 10., 1016/S0016-7037(67)80054-1</ref>

Water from [[dry hole]]s is sometimes analyzed for traces of hydrocarbon-related organic compounds, such as organic acids and benzene. If they are found, it suggests that the formation had an oil [[accumulation]] in the vicinity.<ref name=pt05r175>Zarella, W. M. 1967, Analysis and significance of hydrocarbons in subsurface brines: Geochimica et Cosmochimica Acta, n. 13, p. 1155–1166., 10., 1016/S0016-7037(67)80054-1</ref>

Water for subsurface injection should be carefully filtered and analyzed for its chemical composition. Injection water is filtered because it must be free of suspended matter that might plug the rock pores or coat the faces of the grains. This matter might be bacteria or algae and can be mitigated by including bactericides in the water. Harmful matter can also arise from corrosion of the steel pipes, so it is customary to keep dissolved oxygen out of the injection water. (For information on corrosion and scale, see [[Production problems]].)

Water for subsurface injection should be carefully filtered and analyzed for its chemical composition. Injection water is filtered because it must be free of suspended matter that might plug the rock pores or coat the faces of the grains. This matter might be bacteria or algae and can be mitigated by including bactericides in the water. Harmful matter can also arise from corrosion of the steel pipes, so it is customary to keep dissolved oxygen out of the injection water. (For information on corrosion and scale, see [[Production problems]].)

* [[Core description]]

* [[Core description]]

* [[Porosity]]

* [[Porosity]]

* [[Relative permeability]]

* [[Relative permeability]]

* [[Paleontology]]

* [[Paleontology]]

* [[Capillary pressure]]

* [[Capillary pressure]]

* [[Permeability]]

* [[Permeability]]

* [[SEM, XRD, CL, and XF methods]]

* [[SEM, XRD, CL, and XF methods]]

* [[Thin section analysis]]

* [[Thin section analysis]]

* [[Rock-water reaction: Formation damage]]

* [[Rock-water reaction: formation damage]]

* [[Overview of routine core analysis]]

* [[Overview of routine core analysis]]

* [[Core-log transformations and porosity-permeability relationships]]

* [[Core-log transformations and porosity-permeability relationships]]

[[Category:Laboratory methods]]

[[Category:Laboratory methods]]