Really logs provide understanding of the structures and you may criteria throughout the subsurface, aligned mainly within detection and you may analysis out-of possibly productive limits.
Commitment of saturation
Water saturation ‘s the tiny fraction of pore amount of new tank rock that’s filled Cairns legit hookup sites up with water. It’s fundamentally assumed, except if if not understood, that the pore regularity not filled with liquids is full of hydrocarbons. Determining liquid and you can hydrocarbon saturation is just one of the earliest objectives from well logging.
Clean formations
All-water saturation determinations regarding resistivity logs in clean (nonshaly) formations having homogeneous intergranular porosity are derived from Archie’s liquid saturation formula, or distinctions thereof. [1] [2] The fresh new equation try
To possess simplicity, the latest saturation exponent n can often be pulled because dos. Lab tests show this are a fair really worth to have average instances. For lots more exacting work, electric specifications towards cores will write ideal numbers to possess n, an excellent, and you will meters. Whenever center counted beliefs are unavailable, the costs of good and m within the Eq. 4 will be projected the following: inside the carbonates, F=1/? dos is oftentimes put; for the sands, F=0.62/? dos [3] (Modest formula), or F=0.81/? 2 (a less strenuous means virtually equivalent to this new Very humble algorithm). Such equations can be programmed for the spreadsheets and are also for sale in very diary translation 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.
Alternate strategies for determining h2o saturation become analysis out of cores cut that have reduced-attack petroleum-oriented muds (OBMs) and you can unmarried really chemicals tracer (SWCT) testing. This type of independent tips 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.