Petroleum System Analysis

Petroleum systems analysis (PSA) aims to understand oil and gas occurrence as part of an entire system, both from a geochemically driven “top-down” (oil/gas to sources) and a modelling-driven “bottom-up” (sources to oil/gas) approach.

Geochemical analysis is part of the PSA which aims to interpret and correlate observations and measurements of oils, gases and source rocks and to put them into the overall context of one or more petroleum systems. Geochemical analysis includes (1) Oil and gas analysis: composition and origin of oil and gas, thermal maturity, fingerprinting, oil-oil and oil-source correlations and mixing of oils; (2) Source rock characterization: depositional environment, potential for oil and gas, total organic carbon, thermal maturity and transformation ratio.

 Typical questions in the exploration for conventional oil and gas prospects which can be addressed by PSA include;

• What type of oil and gas is present in the study area?
• Can the oil be tied to a known source rock?
• Could there be two sources for the sampled oil?
• Are gases biogenic or thermogenic?
• What type of fractionation and alteration processes might have occurred?

• What kind of source rock is indicated by the known oils?
• What is its generative potential?

• Is a given source rock likely to have generated oil and/or gas?
• In which part of the basin?
• At what time in the geological history hydrocarbons were generated?

• Are there significant amounts of oil or gas retained in the source rock?
• What could be the expulsion product of a source rock at different maturity levels?
• Where do migrating hydrocarbon focus?
• What is the prospect drainage area and the expelled oil and gas volume within this area?
• Is a given conventional prospect likely to be charged from a specific source rock?
• Which other source rocks might contribute to the prospect charge, and how do hydrocarbons mix?
• Does the charge pre-date the trap formation?

• Where to expect oil and/or gas accumulations?
• What could be the composition and phase?
• What is the chance of success for fill-to-spill oil charge?
• Where is the transition between shale oil and shale gas?

BPSM and PSA results are standard input for common risk segment maps for source rock effectiveness and charge access, as well as for block ranking. Charge volumes and hydrocarbon phase can be estimated for conventional prospect assessment, and in-place retained oil and gas for shale prospects.