29 Sep F is often taken from brand new mentioned porosity of the formation from dating

Better logs promote insight into the brand new structures and you will criteria from the subsurface, aimed mainly at the detection and you can evaluation of perhaps active limits.

Dedication out-of saturation

Water saturation ‘s the tiny fraction of pore number of the latest reservoir material that’s filled with h2o. It is basically presumed, unless of course if you don’t known, your pore volume perhaps not full of water is full of hydrocarbons. Choosing liquid and you may hydrocarbon saturation is just one of the basic objectives from really signing.

Clean structures

All water saturation determinations of resistivity logs when you look at the brush (nonshaly) formations which have homogeneous intergranular porosity are based on Archie’s h2o saturation equation, or distinctions thereof. [1] [2] The new picture try

For convenience, this new saturation exponent n often is drawn since dos. Lab studies show this try a reasonable worth getting mediocre times. For more exacting functions, electronic proportions towards the cores will develop ideal amounts for letter, good, and m. Whenever center measured values try unavailable, the values from a great and you can meters in the Eq. cuatro will likely be estimated the following: in the carbonates, F=1/? dos is commonly made use of; from inside the sands, F=0.62/? dos [3] (Very humble formula), otherwise F=0.81/? 2 (a simpler function around equivalent to the brand new Simple formula). These types of equations are often set towards the spreadsheets and generally are for sale in really diary translation app.

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: R_w, F, and R_t. 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 = R_t.” 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 R_w 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.

Option tricks for choosing liquids saturation is data from cores cut with reasonable-attack petroleum-built muds (OBMs) and solitary better agents tracer (SWCT) tests. These types of independent measures can be used to calibrate log analyses.

Resistivity versus. porosity crossplots

Eq. 7 shows that for R_w constant, ?S_w 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, S_w = 1 and R_t = 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 S_w will also fall on a straight line, because in Eq. 7 the coefficient is constant for Dayton best hookup sites constant values of R_w and S_w.

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 S_w = 1 is drawn from the pivot point (? = 0, R_t = ?) through the most northwesterly plotted points. The slope of this line defines the value of R_w 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 R_w = R₀/F, R_w = 0.065 ohm•m, as shown.