Better logs promote understanding of the latest formations and you will standards regarding the subsurface, aimed generally at detection and you can comparison out of perhaps effective perspectives.
Dedication of saturation
Liquid saturation is the small fraction of your pore amount of the newest tank material which is filled up with h2o. It is basically thought, except if otherwise known, that pore regularity maybe not full of liquids is filled with hydrocarbons. Deciding water and you may hydrocarbon saturation is one of the first expectations of well logging.
Brush formations
All water saturation determinations off resistivity logs inside the brush (nonshaly) formations that have homogeneous intergranular porosity derive from Archie’s liquid saturation formula, otherwise variations thereof. [1] [2] The new picture are
For convenience, the saturation exponent n is usually pulled because the 2. Laboratory experiments demonstrated this particular is a good really worth to own average instances. To get more exacting performs, electric specifications to your cores commonly develop greatest numbers having n, good, and you may meters. Whenever center mentioned beliefs are unavailable, the values from a great and you will meters in the Eq. cuatro is going to be estimated below: within the carbonates, F=1/? 2 is oftentimes utilized; into the sands, F=0.62/? 2 [3] (Simple algorithm), or F=0.81/? dos (a less complicated means practically equal to this new Very humble formula). This type of equations are typically set into spreadsheets and are generally in very journal 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 dating a chinese girl 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 approaches for deciding h2o saturation tend to be study regarding cores reduce which have reasonable-attack oil-based muds (OBMs) and solitary really chemical compounds tracer (SWCT) testing. Such separate methods can be used to calibrate journal analyses.
Resistivity vs. 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.