WELLOG                         WATER SATURATION


REVISED  08-08-2007

2006-2007 WELLOG

All Rights Reserved


Determination of water saturation is the ultimate objective in oil well log analysis.



Basic determinations have historically been made using the following methods:


Keep in mind many factors influence the bottom line in well log interpretation and log analysis. These equations only form a starting point not the final answer!




                        Sw       =         (Ro/Rt)1/2




                        Sw       =         (F * Rw/Rt)1/2




                        Sw       =         (1/ Fm * Rw/Rt)1/2





Improved Water saturation results are obtained using corrected porosity. Porosity may need correction for shale and other out of matrix errors.



                        Sw       =         ((.81 * Rw/Rt)1/2 (Vsh * Rw /.4 Rsh))/ F Fertl Equation



                        Sw       =         ((a * Rw)/( (Fe/(1-Vsh))m  * (1-Vsh)/(1/Rt Vsh/Rsh)))1/n          Laminar Equation           



                        Sw       =         ((a * Rw) * (1/Rt Vsh/Rsh)/ ( (Fe/(1-Vsh))m ))1/n                       Parabolic Equation



Sw       =         ((a * Rw) * (1/Rt Vsh/Rc)/ ( (Fe/(1-Vsh))m ))1/n                         Hossin Equation           



                        Sw       =         (1/ Fsd) * (Rw/Rt)1/2 Vsh * (Rw/Rc)1/2                                    Doll Equation



Sw = Click for (Simandoux) Simandoux Equation






A nomograph can provide a quick way to analyze log data and determine water saturation.




Barrels of oil determination as follows:



Oil Reserve (Recoverable oil) bbls =         (7758.4 * F * (1-Sw) * Recovery factor * h * A/FVF



FVF = Formation Volume Factor



Recovery Factor:


Calculation of Recovery Factor value is complex. Recovery factor will vary with the producing energy mechanism, hydrocarbon viscosity and geometry, formation permeability, and pore geometry. Recovery factor may also be considered in terms of both recovery by primary production and by total recovery after secondary recovery operations. As a rule of thumb one may use a recovery factor of 30 percent for solution gas drive reservoirs, 50 percent for gas cap drive reservoirs, and 70 percent for water drive reservoirs.


Formation volume factor:


Formation volume factor is the space in the producing formation occupied by one barrel of stock tank oil. FVF is generally estimated by adding .05 for each 100 cubic feet of gas produced with each barrel of oil to a base value of 1.05. A detailed study of subsurface temperature and pressure, gas and crude oil gravity will result in a more accurate calculation of formation volume factor.


Oil Reserve nomograph



Gas Reserve nomograph 






All measurements come with a certain amount of uncertainty. Learn more about how to quantify uncertainty.




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