US 4,360,359 A · Method for relating shallow electrical anomalies to the presence of deeper hydrocarbon reservoirs

Abstract

A method is provided for evaluation of shallow electrical anomalies to determine which are likely to be caused by seepage from a hydrocarbon reservoir at depth. The method involves geochemical lithological, and petrographic analyses of anomalous sediments to determine whether these sediments contain certain features characteristic of seepage-induced anomalies. These features include the following: (1) accumulations of seeped (non-indigenous) hydrocarbons; (2) accumulations of carbonate cements that have .delta..sup.13 C values between -10 and -58.degree./oo; (3) pyrite accumulations in a shallow, porous host rock where the pyrite is distributed within fractures or between original grains with a disseminated or cement-like texture, and where it is not associated with kerogen or coal and is not framboidal in morphology; (4) close proximity of said pyrite and carbonate accumulations; and (50 anomalous (high) induced polarization (I.P.) response in conjunction with high apparent resistivity where analyses show the sediments to be in anhydrite-poor formations; and high I.P. response in conjunction with low apparent resistivity where analyses show the sediments to be in anhydrite-rich formations.

Claims24

Dependent claims

A method for detecting subterranean hydrocarbon deposits comprising:

(a) surveying earth formations by induced polarization to detect an electrical anomaly,
(b) sampling said anomalous earth formations
(c) analyzing said anomalous earth formations to determine whether said anomalous earth formation contains metallic sulfides which are not spacially associated with kerogen or coal, and when said anomalous earth formations contain metallic sulfides that are not associated with kerogen or coal, thereafter,
(d) analyzing said anomalous earth formations to determine whether the anomaly is caused by seeped hydrocarbons, hydrocarbon-induced anomalies indicated by
(1) accumulations of seeped gases as determined by C.sub.1 to C.sub.4 hydrocarbon concentration in ppm exceeding .sub.10 (2+10 (TOC in %)), where TOC=total organic carbon concentration and where methane has a .delta..sup.13 C value between -58.degree. and -30.degree./oo;
(2) accumulations of seeped oils where ground sample analyses show
(a) (HC)/(OC) ratios greater than 20, where HC=C.sub.15 and heavier hydrocarbon concentrations in ppm and OC=percent total organic carbon multiplied by 100;
or
(b) (HC)/(OC) ratios between 2 and 20, where indigenous organic carbon is gas-prone;
or
(c) Peak I/Peak II ratios, determined by temperature-programmed pyrolysis greater than 1, and/or
(3) accumulations of seeped oils where data from headspace plus cuttings gases of canned samples show ##EQU4## greater than 0.5 or ##EQU5## greater than 1, where the indigenous organic carbon is dry gas-prone.

9 more elements

A method for detecting subterranean hydrocarbon deposits comprising:

(a) surveying earth formations by induced polarization to detect an anomaly,
(b) sampling said anomalous earth formations
(c) sampling adjacent non-anomalous earth formations from equivalent portions of the geologic section,
(d) analyzing and comparing said anomalous and non-anomalous earth formations to determine whether the anomalous earth formations contain higher concentrations of metallic sulfides not associated with kerogen or coal than the non-anomalous earth formation and where said anomalous earth formations contain higher concentrations of such sulfides, thereafter,
(e) determining whether the anomaly is caused by seeped hydrocarbons by comparing the sampled anomalous earth formation to the sampled non-anomalous adjacent formations, wherein seeped hydrocarbon presence or effect is confirmed when in comparison to adjacent earth formation samples the sampled anomalous earth formation itself contains higher
(1) accumulations of seeped gases, as determined by C.sub.1 to C.sub.4 hydrocarbon concentration in ppm exceeding .sub.10 (2+10 (TOC in %)), where TOC=total organic carbon concentration and where methane has .delta..sup.13 C value between -58.degree. and -30.degree./oo;
(2) accumulations of seeped oils, as determined by ground sample analyses showing
(a) (HC)/(OC) ratios greater than 20, where HC=C.sub.15 heavier hydrocarbon concentrations in ppm and OC=percent total organic carbon multiplied by 100;
or
(b) (HC)/(OC) ratios between 2 and 20, where indigenous organic carbon is gas-prone;
or
(c) Peak I/Peak II ratios, determined by temperature-programmed pyrolysis, greater than 1,
(3) accumulations of seeped oils as determined by data from headspace plus cuttings gases of canned samples showing ##EQU6## greater than 0.5 or ##EQU7## greater than 1, where the indigenous organic carbon is dry gas-prone.

10 more elements

An improved method of hydrocarbon exploration utilizing an electromagnetic method to investigate a polarizable stratum below the surface of the earth, said stratum being indicative of the presence of a hydrocarbon deposit lower than said stratum, by:

(a) implanting in electrical communication with said stratum spaced electrode means to generate a current which flows through paths at a depth in said stratum and to detect voltage resulting from the interception of these current flow paths;
(b) determining the characteristics of said generated current and corresponding detected voltage;
and
(c) utilizing said current and voltage characteristics to determine anomalies resulting from said stratum, the improvement comprising evaluating the source of the anomalies to see if they are caused by seeped hydrocarbons from remote deposits, said hydrocarbon presence or effect of said hydrocarbon presence indicated by
(1) sampling said anomalous earth formation to determine whether said formation contains metallic sulfides not associated with kerogen or coal, and when said anomalous earth formations contain metallic sulfides not associated with kerogen or coal, thereafter
(2) analyzing said anomalous earth formations to determine whether the anomaly is caused by seeped hydrocarbon effect, hydrocarbon-induced anomalies indicated by comparing the sampled anomalous earth formations to surrounding non-anomalous earth formations, wherein the anomalous earth formation contains higher:
(1) accumulations of seeped gas, as determined by C.sub.1 to C.sub.4 hydrocarbon concentration in ppm exceeding .sub.10 (2+10 (TOC in %)), where TOC=total organic carbon concentration and where methane has a .delta..sup.13 C value between -58.degree. and -30.degree./oo;
(2) accumulations of seeped oils, as determined by ground sample analyses showing
(a) (HC)/(OC) ratios greater than 20, where HC=C.sub.15 and heavier hydrocarbon concentrations in ppm and OC=percent total organic carbon multiplied by 100:
or
(b) (HC)/(OC) ratios between 2 and 20, where indigenous organic carbon is gas-prone;
or
(c) Peak I/Peak II ratios, determined by temperature-programmed pyrolysis, greater than 1,
(3) accumulations of seeped oils as determined by data from headspace plus cuttings gases of canned samples showing ##EQU8## greater than 0.5 or ##EQU9## greater than 1, where the indigenous organic carbon is dry gas-prone.

11 more elements

A method for detecting subterranean hydrocarbon deposits comprising:

(a) surveying earth formations by induced polarization to detect an anomaly,
(b) sampling said anomalous earth formations
(c) sampling adjacent non-anomalous earth formations,
(d) analyzing and comparing said anomalous and non-anomalous earth formations to determine whether the anomalous earth formations contain higher concentrations of metallic sulfides not associated with kerogen or coal than the non-anomalous earth formation and where said anomalous earth formations contain higher concentrations of such sulfides, thereafter,
(e) determining whether the anomaly is caused by seeped hydrocarbons by comparing the sampled anomalous earth formation to be sampled non-anomalous adjacent formations, wherein seeped hydrocarbon presence or effect is confirmed when in comparison to adjacent earth formation samples the sampled anomalous earth formation itself contains higher accumulations of carbonate cements having .delta..sup.13 C values between -10.degree. and -58.degree./oo.

2 more elements

(a) implanting in electrical communication with said stratum spaced electrode means to generate a current which flows through paths at a depth in said stratum and to detect voltage resulting from the interception of these current flow paths;
(b) determining the characteristics of said generated current and corresponding detected voltage;
and
(c) utilizing said current and voltage characteristics to determine anomalies resulting from said stratum, the improvement comprising evaluating the source of the anomalies to see if they are caused by seeped hydrocarbons from remote deposits, said hydrocarbon presence or effect of said hydrocarbon presence indicated by
(1) sampling said anomalous earth formation to determine whether said formation contains metallic sulfides not associated with kerogen or coal, and when said anomalous earth formations contain metallic sulfides not associated with kerogen or coal, thereafter
(2) analyzing said anomalous earth formations to determine whether the anomaly is caused by seeped hydrocarbon effect, hydrocarbon-induced anomalies indicated by comparing the sampled anomalous earth formations to surrounding non-anomalous earth formations, wherein the anomalous earth formation contains higher accumulation of carbonate cements having .delta..sup.13 C values between -10.degree. and -58.degree./oo.

3 more elements

Dependencies are inferred from the claim text.

Method for relating shallow electrical anomalies to the presence of deeper hydrocarbon reservoirs

Life of this patent

Method for relating shallow electrical anomalies to the presence of deeper hydrocarbon reservoirs

Life of this patent

Abstract

Claims24