F can often be taken from new counted porosity of formation through the relationships

02 Oct F can often be taken from new counted porosity of formation through the relationships

Well logs offer insight into the fresh new structures and requirements regarding the subsurface, aimed mostly during the detection and you may research away from perhaps effective horizons.

Commitment off saturation

Liquids saturation is the fraction of the pore number of the latest tank material which is full of liquids. It is basically believed, except if if you don’t understood, the pore frequency maybe not full of water is full of hydrocarbons. Determining liquids and you may hydrocarbon saturation is amongst the very first objectives out-of well signing.

Clean structures

All-water saturation determinations of resistivity logs in the clean (nonshaly) formations which have homogeneous intergranular porosity derive from Archie’s h2o saturation formula, otherwise distinctions thereof. [1] [2] The picture are

To possess convenience, the new saturation exponent n is frequently drawn because the 2. Laboratory studies have demostrated this was a reasonable value getting mediocre instances. For more exacting work, electric measurements toward cores will create top numbers to have n, a good, and you may meters. Whenever key mentioned beliefs was unavailable, the costs out-of an effective and yards inside the Eq. cuatro will likely be projected below: in the carbonates, F=1/? 2 can often be put; from inside the sands, F=0.62/? 2 [3] (Simple algorithm), otherwise F=0.81/? dos (a simpler setting almost equivalent to the fresh new Simple algorithm). These types of equations are often programmed with the spreadsheets and they are available in really log 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.

Alternate tricks for determining liquid saturation include investigation regarding cores cut having reduced-intrusion oil-established muds (OBMs) and you will unmarried well agents tracer (SWCT) assessment best hookup apps Richmond Virginia. This type of separate methods are often used to calibrate diary analyses.

Resistivity against. 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 ohm•m, as shown.