Really logs provide understanding of this new formations and you will conditions from the subsurface, lined up mainly at the detection and comparison from possibly effective perspectives.
Dedication from saturation
Liquids saturation ‘s the small fraction of your pore level of the new tank stone which is full of h2o. It is generally presumed, until otherwise understood, your pore regularity perhaps not filled up with liquids is stuffed with hydrocarbons. Deciding liquids and you may hydrocarbon saturation is one of the earliest expectations out-of better logging.
Brush formations
All water saturation determinations off resistivity logs within the clean (nonshaly) structures that have homogeneous intergranular porosity depend on Archie’s liquid saturation formula, or distinctions thereof. [1] [2] The newest equation is
Getting convenience, new saturation exponent n is often drawn while the dos. Laboratory experiments show this is a fair worthy of having average circumstances. To get more exacting functions, electronic measurements towards cores tend to establish finest wide variety for n, a, and you may m. When key mentioned opinions is unavailable, the costs regarding a good and meters when you look at the Eq. 4 is projected the following: into the carbonates, F=1/? 2 is usually put; into the sands, F=0.62/? 2 [3] (Modest formula), otherwise F=0.81/? 2 (an easier setting practically comparable to this new Humble formula). These types of equations can be programmed into the spreadsheets and therefore are found in really log 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.
Solution strategies for determining drinking water saturation tend to be study away from cores reduce with lowest-intrusion oils-created muds (OBMs) and you may solitary really toxins tracer (SWCT) tests. This type of independent steps are often used to calibrate record analyses.
Resistivity compared to. 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 https://datingranking.net/local-hookup/fort-lauderdale/ 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.