Really logs give understanding of the new formations and you may requirements on subsurface, aimed generally at the detection and assessment out-of maybe effective horizons.

Devotion out of saturation

Drinking water saturation ‘s the fraction of the pore volume of the fresh reservoir material which is filled with drinking water. It’s generally thought, until or even understood, that the pore regularity not filled up with liquid is filled with hydrocarbons. Deciding h2o and you can hydrocarbon saturation is among the first objectives away from well logging.

Brush formations

All-water saturation determinations off resistivity logs from inside the clean (nonshaly) structures having homogeneous intergranular porosity derive from Archie’s liquid saturation picture, or differences thereof. [1] [2] This new picture is actually

To own simplicity, the new saturation exponent letter is oftentimes taken because 2. Research experiments have shown that this was a fair worthy of for mediocre times. To get more exacting functions, electronic measurements into the cores usually produce ideal wide variety to have letter, a good, and yards. When core measured beliefs is actually not available, the costs regarding a good and you can yards in Eq. cuatro is estimated as follows: in carbonates, F=1/? 2 might be put; inside sands, F=0.62/? dos [3] (Simple algorithm), or F=0.81/? 2 (a simpler mode virtually equal to the Very humble algorithm). These equations can be developed with the spreadsheets and are usually in extremely record 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: 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.

Solution tricks for choosing liquids saturation is analysis regarding cores slashed that have low-intrusion petroleum-created muds (OBMs) and you may single really agents tracer (SWCT) evaluation. These independent strategies are often used to calibrate record 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 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 Cambridge hookup apps ohm•m, as shown.