Method for determining reservoir bulk volume of hydrocarbons from reservoir porosity and distance to oil-water contact level

A method for determining bulk volume of oil (BVO or .phi..sub.o) as a function of depth above initial oil-water contact and effective porosity in a zone of a well in which a log of effective porosity .phi..sub.E exists and at least one other log exists from which a log of water saturation S.sub.wi may be derived, said logs having been made before any significant water table movement occurred, comprising the steps of

• identifying the initial oil-water contact depth z.sub.c from one of said logs,
• determining a log of water saturation S.sub.wi as a function of depth in the well z from said existing logs,
• determining a log of bulk volume of oil .phi..sub.o from said log of water saturation S.sub.wi as a function of distance h=z-z.sub.c above the oil-water contact depth,
• determining the constants C, K, and g from multiple equations of the form,
• .phi..sub.o (h)=C.phi..sub.E (h)-K+g log h
• where numerical values of .phi..sub.o and .phi..sub.E are determined as respective logs at distinct values of h, and
• recording a log of .phi..sub.o (h) by combining .phi..sub.E (h) data from a log of effective porosity for said zone.

A method for determining the level of oil-water contact of a reservoir where wells do not penetrate the oil-water contact level of said reservoir, but capillary pressure data are available from analysis of cores taken from a first well and a well log of the reservoir of effective porosity .phi..sub.E exists and at least one other well log of the reservoir exists from which a log of water saturation S.sub.wi may be derived, comprising the steps of

• determining from said capillary pressure data from said cores a relationship of bulk volume of oil (.phi..sub.o) as a function of total porosity .phi..sub.E of the formation and height h above the oil-water contact level of the reservoir of the form,
• h=10.sup.(.phi..sbsp.o.sup.-C.phi..sbsp.E.sup.+K)/g,
• where the constants C, K, and g are determined,
• determining a log of water saturation S.sub.wi as a function of depth z in said first well from said existing logs,
• determining a log of bulk volume of oil .phi..sub.o from said log of water saturation S.sub.wi as a function of depth z in said first well, and
• determining the oil-water contact level WL as a function of a plurality of depths z in said first well as
• WL(z)=z+h(z)
• where h is determined from said relationship,
• h(z)=10.sup.(.phi..sbsp..sup.(z)-C.phi..sbsp.E.sup.(z)+K)/g.

A method for determining bulk volume of oil (BVO or .phi..sub.o) as a function of depth and effective porosity in a zone of a produced well in which a log of effective porosity .phi..sub.E exists comprising the steps of,

• obtaining core samples from said zone corresponding to said zone of said produced well,
• testing said core samples to determine a first relationship of bulk volume of oil (BVO or .phi..sub.o) as a function of capillary pressure P.sub.c and effective porosity .phi..sub.E, that is, .phi..sub.o =f(.phi..sub.E, P.sub.c),
• determining the correspondence between capillary pressure P.sub.c, and height h above the oil-free water contact of the zone of the form, ##EQU14## where d.sub.w is the density of the connate water of the zone, d.sub.o is the density of oil in the zone, and K.sub.1 is a constant of proportionality,
• determining a second relationship of bulk volume of oil (BVO) as a function of total porosity .phi..sub.E of the formation and height h above the oil water contact depth of the zone of the form,
• .phi..sub.o =C.phi..sub.E -K+(g.times.h),
• where C, and g are numerical constants, and
• recording a log of .phi..sub.o (h) from said second relationship by combining .phi..sub.E (h) data from a log of effective porosity for said zone.