HYDROCARBON EVOLUTION FOR A NORTH-SOUTH SECTION OF THE SOUTH CASPIAN BASIN

A 150 km length, 6-second deep, seismic line across the west central a nd north parts of the South Caspian Basin was used to construct quanti tative dynamical, thermal and hydrocarbon evolution patterns. The dept h of the west part of the 2-D section of the South Caspian Basin is al most 30 km. The computer program GEOPETII was used to provide quantita tive evolution models. The procedure provided an opportunity to invest igate the development dynamics of: excess fluid pressure, porosity ret ention, rock fracturing, compaction, heat transfer, maturity, generati on pressure, kinetic hydrocarbon generation, migration and accumulatio n, together with solubility effects on hydrocarbon transport. The resu lts suggest that: (i) Temperature is 350-400 degrees C in the deepest part of the section at a depth of 26-29 km; (ii) The highest values of excess pressure (nearly twice hydrostatic fluid pressure) are in Jura ssic and Cretaceous formations in the west part of the section, which has now subsided to a depth of about 20-27 km; (iii) Major oil and gas generation began in the last 10-5 MYBP, the migration in free-phase a nd in water solution occurring dominantly in the last few million year s; (iv) Trapping of hydrocarbons took place mainly, but not exclusivel y, in the 3-9 km depth interval in the sands of the Productive Series of the Pliocene, embedded in a shale sequence; (v) Oil and gas filling of the shallow reservoirs by oil and gas is on-going today, indicatin g an extremely high productivity for any reservoir found in the offsho re area; (vi) There is overlap with depth of oil and gas reservoirs, a nd the total amount of hydrocarbons estimated to be trapped is conside rable; (vii) The high overpressure expected makes for a drilling hazar d, but one which it is worthwhile to overcome if the anticipated oil a nd gas accumulations are encountered. (C) 1998 Elsevier Science Ltd. A ll rights reserved.