Saturation exponent

The volume fraction of water (S J and the saturation exponent n can be considered as expressing the increased difficulty experienced by an electrical current passing through a partially oil filled sample. (Note is only a special case of C, when a reservoir... 

This paper reports an investigation of the effects of porous solid structures on their electrical behaviour at different frequencies (from 100 Hz to 100 kHz). For that, we study different parameters such as formation resistivity factor, cementation factor, chargeability, resistivity index and saturation exponent. Different porous solid structures are quantified from the petrographic image analysis and Hg-injection technique. Then, by using different models we obtain the permeability prediction from the electrical behaviour and structure parameters. 

Samples used in this study, their formation, petrographic, petrophysical and mineralogical characteristics. C crystal carbonate M-W mudstone, wackestone P-G packstone-grainstone Vac vugs iX intercrystalline pores iM intramatrix pores iG intragranular pores IG intergranular pores K karsts Fr fractures F formation factor m cementation factor n saturation exponent. 

In the case of drainage, the end-point relative permeability and saturation exponent for the non-wetting phase can be related to the dimensionless rate. These parameters increase as the dimensionless rate increases. 

The saturation exponent in the wetting phase relative permeability functional form decreased with an increase in rate. 

F formation factor, m cementation factor n saturation exponent water porosity water permrability (mD) ... 

Table I and Figure 3 give the relationship between logiR - logSw and the saturation exponent n whose values range between 1.2 and 3.5. The hig)iest values of n are obtained for the dolomite crystal carbonate (n = 3.5) while the lowest values of n are obtained for the mudstone-wackestone texture (n = 1.2).

More than thirteen carbonate samples are studied to measure classic electric parameters in saturated and unsaturated geological carbonate porous systems. The values of the cementation factor m range finm 1.55 to 2.49. The dolomitic crystal texture shows the highest value. The electrical behaviour of the carbonate porous system in a unsaturated medium is studied from the saturation exponent n. The highest values of n are obtained for a dolomite crystal carbonate (n = 3.5) while the lowest values of n are obtained for a mudstone-wackestone texture (n = 1.2). The values of the chargeability factor M range between 0.19 and 0.5, and they depend on the brine/gas saturation of the carbonate porous system, carbonate textures and the salinity of brine in a porous medium. 

Network-based flow relations capillary pressure as a functiOTi of water saturation, relative permeability as a function of water saturatiOTi, Resistivity Index as a function of water saturation, and corresponding saturation exponent n for both primary drainage and imbibition cycle. 

The saturation exponent must be determined experimentally in core laboratories. It is controlled by the distribution of the conducting brine in the pore space, thus depending on the rock texture, wetting properties, and "saturation history" caused by capillary effects. 

Different saturating techniques (imbibitirMi, drainage) and techniques of core preparation also affect the laboratory-determined saturation exponent (see, for example, de Waal et al., 1989 Sharma et al., 1991 Worthington and PaUatt, 1990 Worthington et al., 1989, 1988). 

In carbonates, the heterogeneity of the pore space again results in more complicated plots IR versus 5w for the saturation exponent. Ellis and Singer (2007) note Carbonates are particularly heterogeneous, and are also more likely to be oil-wet, so that for both reasons the relation between resistivity and is likely to be complicated, with n not equal to 2 and also varying with saturation . 

The modular concept can also be applied on bi- or multi-modal sand it gives an explanation of a saturation-dependent saturation exponent n (Schon et al., 2000). The concept is widely used for the interpretation of measurements with orthogonal induction systems in well logging. 

WOTthingtrm, PJ., Pallatt, N., 1990. EffetJ of variable saturation exponent irpon the evaluation of hydrocarbon saturation hr Presented at the SPE Annital Technical Crmfermce and Exhibition, New Orleans, LA, Septmrber. PapCT SPE 20538. 

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