Really logs render insight into the formations and you will requirements on the subsurface, aligned primarily on recognition and you may assessment out of maybe productive perspectives.

## Dedication out-of saturation

Liquids saturation ‘s the tiny fraction of pore volume of the fresh reservoir stone that’s full of liquids. It is essentially believed, unless of course otherwise known, the pore frequency not filled with drinking water is full of hydrocarbons. Determining water and you can hydrocarbon saturation is amongst the very first objectives regarding better signing.

## Clean formations

All-water saturation determinations off resistivity logs for the brush (nonshaly) structures with homogeneous intergranular porosity are based on Archie’s h2o saturation picture, otherwise variations thereof. [1] [2] The newest picture are

For convenience, brand new saturation exponent n is frequently pulled just like the dos. Laboratory experiments have indicated that this was a good value for mediocre instances. For lots more exacting performs, electricity proportions to the cores commonly establish ideal wide variety getting letter, a great, and yards. Whenever key counted thinking was not available, the costs of a good and you may meters during the Eq. 4 shall be estimated as follows: from inside the carbonates, F=1/? 2 is normally made use of; inside sands, F=0.62/? dos [3] (Simple formula), or F=0.81/? dos (an easier form about equivalent to new Humble algorithm). This type of equations can be set toward spreadsheets and are for sale in extremely 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: 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 strategies for determining water saturation is analysis out-of cores clipped having reduced-attack petroleum-established muds (OBMs) and you can unmarried really toxins tracer (SWCT) screening. This type of independent steps can be used to calibrate journal analyses.

## Resistivity compared to. 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} = R_{0}. If R_{0} 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%, R_{0} = 6.5 ohm•m. For this formation, the most appropriate F – ? relation is F = 1/? 2 . Thus, for ? = 10%, F = 100. Because R_{w} = R_{0}/F, R_{w} = Charlottetown hookup 0.065 ohm•m, as shown.

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