Changes

==Hydrocarbon composition from microseeps==

==Hydrocarbon composition from microseeps==

Obtaining compositional information from the analysis of hydrocarbon microseeps is more difficult because microseeps generally consist of only light hydrocarbons (methane through pentane). Sometimes, however, the heavier gasoline-range and aromatic hydrocarbons are also present. One can infer the composition of the migrating petroleum from these light hydrocarbons from soil gas/hydrocarbon ratios, carbon isotopic composition of soil gases, fluorescence characteristics of soil or sediment extracts, and chromatographic analysis of such extracts. A detailed discussion of these methodologies is beyond the scope of this article, but published examples of such analyses and their interpretations include Abrams<ref name=ch18r3>Abrams, M., A., 1996, [http://archives.datapages.com/data/specpubs/memoir66/22/0309.htm Interpretation of methane carbon isotopes extracted from surficial marine sediments for detection of subsurface hydrocarbons], in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 309–318.</ref> Barwise and Hay<ref name=ch18r6>Barwise, T., Hay, S., 1996, [http://archives.datapages.com/data/specpubs/memoir66/28/0363.htm Predicting oil properties from core fluorescence], in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 363–371.</ref> Belt and Rice<ref name=ch18r8>Belt, J., Q., Rice, G., K., 1996, Offshore 3D seismic, geochemical data integration, Main Pass project, Gulf of Mexico: Oil & Gas Journal, vol. 94, no. 14, p. 76–81, and vol. 94, no. 15, p. 100–102.</ref> Brooks et al.<ref name=ch18r9>Brooks, J., M., Kennicutt, M., C., Carey, B., D., 1986, Offshore surface geochemical exploration: Oil & Gas Journal, October 20, p. 66–72.</ref> Horvitz<ref name=ch18r16>Horvitz, L., 1985, Geochemical exploration for petroleum: Science, vol. 229, p. 821–827., 10., 1126/science., 229., 4716., 821</ref> Jones and Drozd<ref name=ch18r17>Jones, V., T., Drozd, R., J., 1983, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0067/0006/0900/0932.htm Predictions of oil or gas potential by near-surface geochemistry]: AAPG Bulletin, vol. 67, p. 932–952.</ref> Kornacki<ref name=ch18r20>Kornacki, A., S., 1996, Petroleum geology and geochemistry of Miocene source rocks and heavy petroleum samples from Huasna Basin, California, in Schumacher, D., Abrams, M. A., eds., Hydrocarbon Migration and Its Near-Surface Expression: AAPG Memoir 66, p. 413–430.</ref> Piggot and Abrams<ref name=ch18r28>Piggott, N., Abrams, M., A., 1996, Near-surface coring in the Beaufort and Chukchi Seas, northern Alaska, in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: AAPG Memoir 66, p. 385–399.</ref> Schiemer et al.<ref name=ch18r38>Schiemer, E., J., Stober, G., Faber, E., 1985, Surface geochemical exploration for hydrocarbons in offshore areas—principles, methods and results, in Petroleum Geochemistry in Exploration of the Norwegian Shelf: London, Graham and Trotman, p. 223–238.</ref> Stahl et al.<ref name=ch18r42>Stahl, W., Faber, E., Carey, B., D., Kirksey, D., L., 1981, Near-surface evidence of migration of natural gas from deep reservoirs and source rocks: AAPG Bulletin, vol. 65, p. 1543–1550.</ref> and Thrasher et al..<ref name=ch18r45>Thrasher, J., A., Strait, D., Lugo, R., A., 1996a, Surface geochemistry as an exploration tool in the South Caribbean, in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: AAPG Memoir 66, p. 373–384.</ref>

Obtaining compositional information from the analysis of hydrocarbon microseeps is more difficult because microseeps generally consist of only light hydrocarbons (methane through pentane). Sometimes, however, the heavier gasoline-range and aromatic hydrocarbons are also present. One can infer the composition of the migrating petroleum from these light hydrocarbons from soil gas/hydrocarbon ratios, carbon isotopic composition of soil gases, fluorescence characteristics of soil or sediment extracts, and chromatographic analysis of such extracts. A detailed discussion of these methodologies is beyond the scope of this article, but published examples of such analyses and their interpretations include Abrams<ref name=ch18r3>Abrams, M., A., 1996, [http://archives.datapages.com/data/specpubs/memoir66/22/0309.htm Interpretation of methane carbon isotopes extracted from surficial marine sediments for detection of subsurface hydrocarbons], in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 309–318.</ref> Barwise and Hay<ref name=ch18r6>Barwise, T., Hay, S., 1996, [http://archives.datapages.com/data/specpubs/memoir66/28/0363.htm Predicting oil properties from core fluorescence], in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 363–371.</ref> Belt and Rice<ref name=ch18r8>Belt, J., Q., Rice, G., K., 1996, Offshore 3D seismic, geochemical data integration, Main Pass project, Gulf of Mexico: Oil & Gas Journal, vol. 94, no. 14, p. 76–81, and vol. 94, no. 15, p. 100–102.</ref> Brooks et al.<ref name=ch18r9>Brooks, J., M., Kennicutt, M., C., Carey, B., D., 1986, Offshore surface geochemical exploration: Oil & Gas Journal, October 20, p. 66–72.</ref> Horvitz<ref name=ch18r16>Horvitz, L., 1985, Geochemical exploration for petroleum: Science, vol. 229, p. 821–827., 10., 1126/science., 229., 4716., 821</ref> Jones and Drozd<ref name=ch18r17>Jones, V., T., Drozd, R., J., 1983, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0067/0006/0900/0932.htm Predictions of oil or gas potential by near-surface geochemistry]: AAPG Bulletin, vol. 67, p. 932–952.</ref> Kornacki<ref name=ch18r20>Kornacki, A., S., 1996, [http://archives.datapages.com/data/specpubs/memoir66/32/0413.htm Petroleum geology and geochemistry of Miocene source rocks and heavy petroleum samples from Huasna Basin, California], in Schumacher, D., Abrams, M. A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 413–430.</ref> Piggot and Abrams<ref name=ch18r28>Piggott, N., Abrams, M., A., 1996, [http://archives.datapages.com/data/specpubs/memoir66/30/0385.htm Near-surface coring in the Beaufort and Chukchi Seas, northern Alaska], in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 385–399.</ref> Schiemer et al.<ref name=ch18r38>Schiemer, E., J., Stober, G., Faber, E., 1985, Surface geochemical exploration for hydrocarbons in offshore areas—principles, methods and results, in Petroleum Geochemistry in Exploration of the Norwegian Shelf: London, Graham and Trotman, p. 223–238.</ref> Stahl et al.<ref name=ch18r42>Stahl, W., Faber, E., Carey, B., D., Kirksey, D., L., 1981, [http://archives.datapages.com/data/bulletns/1980-81/data/pg/0065/0009/1500/1543.htm Near-surface evidence of migration of natural gas from deep reservoirs and source rocks]: AAPG Bulletin, vol. 65, p. 1543–1550.</ref> and Thrasher et al.<ref name=ch18r45>Thrasher, J., A., Strait, D., Lugo, R., A., 1996a, [http://archives.datapages.com/data/specpubs/memoir66/29/0373.htm Surface geochemistry as an exploration tool in the South Caribbean], in Schumacher, D., Abrams, M., A., eds., Hydrocarbon Migration and Its Near-Surface Expression: [http://store.aapg.org/detail.aspx?id=75 AAPG Memoir 66], p. 373–384.</ref>

==See also==

==See also==