Technical risk analysis of the petroleum charge system is a two-step process involving: (1) quantitative and non-quantitative predictions of risk components (source, expulsion, product type, migration, timing, entrapment and porosity) and (2) estimates of the degree of uncertainty (“chance of failure”) for each component. The best predictions of risk components involve the integration of multiple technologies, technical project planning, and cooperative teamwork. Estimating the degree of uncertainty for each risk component is also greatly enhanced by the use of multidisciplinary evaluations, because they are constrained by a wider variety of complementary data types, thereby increasing the degree of confidence in the assignment of risk.

The interpretation of a basin's thermal evolution is fundamental to predicting petroleum charge system risk because of the effect on source rock maturation, hydrocarbon generation and expulsion, migration and entrapment timing, hydrocarbon preservational state and reservoir rock diagenesis and porosity history. The most successful method of thermal history evaluation utilizes a multidisciplinary team approach that includes contributions from the geochemistry, petrology and paleontology disciplines. Recommended analytical procedures that are included in this evaluation are vitrinite reflectance, thermal alteration index, conodont alteration index, Rock-Eval pyrolysis, biomarker analysis, apatite fission track analysis, fluid inclusion petrography, inorganic thermochronology (Helium isotopes, ⁴⁰Ar/³⁹Ar, etc.) and illite crystallinity. Resulting thermal data are then used in conjunction with structural geology data and thermal modeling software to interpret thermal and burial histories. Multidisciplinary maturity studies benefit from improved reliability, greater cost effectiveness and wider applicability (no age, lithology, or structural complexity restrictions). In addition, these techniques provide accessory data that are beneficial to the explorationist, such as source rock geochemistry, kerogen identification, biostratigraphy, paleoenvironmental interpretation, diagenesis, migration and timing, and the timing of heating and cooling events.

The conventional style of thermal history application generally involves the calibration of computer modeling with basic organic maturity data, stratigraphic and lithologic data, and wellbore temperatures to yield an optimized burial and thermal history. Thermal modeling results are usually focused on the interpretation of source rock parameters only (generation/expulsion timing, transformation ratios, etc.). In contrast, we advocate a redesigned style of thermal history application that is an iterative integration and interpretation process geared to address multiple risk parameters. This process includes five stages: (1) technical project planning to select the most appropriate mix of maturity technologies, (2) independent maturity analyses to ensure unbiased data generation and initial interpretations, (3) first-pass integration of maturity datasets and development of preliminary interpretations, (4) optimization of thermal modeling efforts with the previously integrated maturity data in an iterative process designed to provide an overall interpretation of thermal and burial history, and (5) higher-level integration of thermal history interpretations with related technical data sets (e.g., structural geology, geophysics, log analysis, etc.) to address other risk parameters associated with all components of the petroleum charge system (source quality, product type, reservoir quality and the timing of expulsion, migration, re-migration, and entrapment). Examples of successful integrated maturity studies are shown from the USA, the Middle East, China, and the Baltic Sea.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah