Really logs render insight into this new formations and you can requirements about subsurface, aligned generally on identification and review off maybe energetic perspectives.
Dedication out-of saturation
H2o saturation ‘s the tiny fraction of the pore volume of the latest reservoir material which is full of liquids. It’s basically assumed, except if if you don’t understood, that pore frequency maybe not full of h2o is full of hydrocarbons. Choosing water and hydrocarbon saturation is among the first expectations from better signing.
All-water saturation determinations off resistivity logs inside clean (nonshaly) formations with homogeneous intergranular porosity are derived from Archie’s liquid saturation equation, otherwise distinctions thereof.   The latest picture are
To possess simplicity, the newest saturation exponent letter can be pulled due to the fact 2. Lab experiments demonstrate that is a fair well worth to own mediocre times. For lots more exacting works, electronic specifications towards cores often make greatest number having n, a great, and m. Whenever key mentioned values was unavailable, the prices away from a and you may m inside the Eq. cuatro will be estimated below: from inside the carbonates, F=1/? dos is normally utilized; for the sands, F=0.62/? 2  (Humble algorithm), or F=0.81/? dos (a less strenuous mode almost comparable to the latest Very humble algorithm). These types of equations are often developed on the spreadsheets and are generally found in really diary interpretation application.
The accuracy of the Archie equation, Eq. 1 and its derivatives, depends in large measure, of course, on the accuracy of the fundamental input parameters: Rw, F, and Rt. The deep resistivity measurement (induction or laterolog) must be corrected, therefore, for borehole, bed thickness, and invasion (see the page Formation resistivity determination for more details). It is almost never safe to make the assumption “deep = Rt.” The most appropriate porosity log (sonic, neutron, density, magnetic resonance, or other) or combination of porosity and lithology measurements must be used to obtain porosity, and the proper porosity-to-formation factor relationship must be used. Finally, the Rw value should be verified in as many ways as possible: calculation from the SP curve, water catalog, calculation from nearby water-bearing formation, and/or water sample measurement.
Approach tricks for El Paso hookup websites deciding liquids saturation are studies away from cores clipped having reduced-attack oil-centered muds (OBMs) and you may unmarried well chemical tracer (SWCT) evaluation. Such independent strategies are often used to calibrate log analyses.
Resistivity versus. porosity crossplots
Eq. 7 shows that for Rw constant, ?Sw is proportional to is the quantity of water per unit volume of formation. To emphasize the proportionality between ? and , Eq. 7 may be rewritten:
For a 100% water-saturated formation, Sw = 1 and Rt = R0. If R0 for water-saturated formations is plotted on an inverse square-root scale vs. ?, all points should fall on a straight line given by .
Furthermore, the points corresponding to any other constant value of Sw will also fall on a straight line, because in Eq. 7 the coefficient is constant for constant values of Rw and Sw.
Fig. 1 shows several points plotted over an interval in which formation-water resistivity is constant (as indicated by constant SP deflections opposite the thick, clean permeable beds). Assuming that at least some of the points are from 100% water-bearing formations, the line for Sw = 1 is drawn from the pivot point (? = 0, Rt = ?) through the most northwesterly plotted points. The slope of this line defines the value of Rw as shown on Fig. 1, for ? = 10%, R0 = 6.5 ohm•m. For this formation, the most appropriate F – ? relation is F = 1/? 2 . Thus, for ? = 10%, F = 100. Because Rw = R0/F, Rw = 0.065 ohm•m, as shown.