Quantitative evaluation Examine procedures in which data from 2 or more logs will be used to evaluate for the amount of hydrocarbon compared to pore water within a formation The proportion of pore space occupied by water is known as water saturation (S w ) e.g. if 65% of the formation is occupied by water and 35% by hydrocarbons the water saturation is 0.65 (percent water saturation is 65%) Definition of the formation factor (F) F = Ro/Rw Where Ro is the resistivity of the total formation (rock matrix + fluids) saturated with water Rw is the resistivity of the water itself

 F= Formation factor is used to help calculate water saturation – function of porosity  Definition F = R o /R w  Definition for water saturation S w = √R O /R T R O = R T (for a 100% saturated sand)  Substituting in the equations and rewriting for water saturation we have: R O = F. R W S W = F. R W /R T

QUANTITATIVE EVALUATION FOR HYDROCARBON POTENTIAL Archie equation (1942) … F = a/φ m a= constant which is lithology dependent m=empirically derived constant φ=porosity (e.g. 30% enter as 0.30) Actual values for a and m are lithology and region dependent Some examples F = 0.82/φ uncompacted sands F = 1/ φ 2 compacted formations, chalk F = 1/ φ 2.2 compacted clastic and oolitic rocks F = 0.62/ φ 2.15 recrystallized carbonates (sucrosic texture) F = 1.13/φ 1.73 generic value for large number of samples

Analysis for Hydrocarbon Potential Definition:R wa = R t / F  R wa = apparent water resistivity  R t is measured from a deeply focused induction log  F is calculated from the formula using log measured porosity value  est S w (%) = √R w / R wa x 100  R w = R wa of a 100% water saturated formation. Measure from an obvious water-bearing formation  R wa Analysis R wa / R w  Ratio Rwa < 2 No oil production  Ratio Rwa > 4 Oil production expected

Hydrocarbon potential Locations SP mv Resistivity ohm-mφFR wa est S w % Rwa analysis R wa /R w Hydrocarbon Production y/n shdpdp in Use F = 0.83 / φ 2

READINGS AND CALCULATIONS LevelsSP mv Resistivity ohm-mφFR wa est S w % R wa / R w Prod. y/n shdpdp in N N N N Y