Background
The best way to reduce investment risk in oil and gas exploration is to ascertain the presence, types and volumes of hydrocarbons in a prospective structure before drilling. Seismic interpretation can delineate closed structures and identify potential subsurface traps, but it does not reliably predict trap content. Drilling on a closed structure, even near a producing oil or gas field, holds no guarantee that similar fluids will be found. Therefore, profitable exploration requires a methodology to predict the likelihood of success given the available data and associated uncertainties.
Generally, the success of any exploration campaign depends on the convergence of crucial geologic elements (effective source, reservoir, seal and overburden rocks) and processes (hydrocarbon generation, migration and accumulation), defining in a framework which is called petroleum system. The elements and processes must occur in the proper order for the organic matter in a source rock to be converted into petroleum and then to be stored and preserved. If a single element or process is missing or occurs out of the required sequence, a prospect loses viability.
Basin modeling and petroleum system analysis brings together several dynamic processes, including sediment deposition, faulting, burial, kerogen maturation kinetics and multiphase fluid flow. These processes may be examined at several levels and complexity which are typically increases with spatial dimensionality. Briefly, 1D modeling examines burial history at a point location, and 2D modeling, either in map or cross section, can be used to reconstruct oil and gas generation, migration and accumulation along a cross section. 3D modeling reconstructs petroleum systems at reservoir and basin scales and has the ability to display the output in 1D, 2D or 3D, and through time.
Requirements
Depending on the dimensionality of modeling, a variety of data are needed, among which are:
- Locations, depths, and areal distribution of all strata
- Ages and lithologies for all formation intervals
- Time periods and areas of erosion and tectonic events
- Source rock-related geochemical data such as TOC, HI, and kinetics
- Vertical and lateral extent of faults and timing of onset of faulting
- Surface and subsurface temperatures through time such as heat flow history
- Water depth through time
- External calibration data such as DST temperatures and vitrinite reflectance (Ro)
- Petroleum system modeling software (e.g. ThemisFlow, PetroMod, etc.)
Applications
- Burial/thermal/maturation history reconstruction and kitchen evaluation
- Interpretation of paleothermal indicators and thermal regimes
- Assessment of source rock effectiveness
- Assessment of shale potential and identification of sweet spots
- Volumetric estimation of oil and gas generated, expelled, migrated, accumulated
- Understanding of oil families and their corresponding sources
- Ranking of prospects (size, petroleum fluid characteristics, uncertainty)
- Understanding expulsion efficiencies
- Pore pressure history, prediction of present-day overpressures before drilling
- Reconstruction of oil and gas migration pathways and migration efficiencies
- Role of faults in oil and gas migration
- Understanding of origin of gas: biogenic, thermogenic, or non-hydrocarbon gas (CO2).
- Understanding seal efficiency and oil/gas columns
- Post mortem interpretations
- Delineation and development of exploratory areas
- Understanding of oil heterogeneities at field scale
Benefits
- Regional evaluation of petroleum system
- Definition of exploration strategy
- Prospect generation and prospect ranking
- Pre-drill risk assessment, including drilling optimization in overpressured areas
- Fast track evaluation of blocks offered for tendering