Applied Petroleum Geochemistry
An understanding of geochemical principles is essential if we are to further our knowledge of the petroleum systems of basin. As such, a fundamental requirement is an understanding of source rock distribution and quality, and maturation history, where simple rules can be applied to evaluate the hydrocarbon prospectivity of different parts of a basin.
Trends in source richness, maturity and hydrocarbon potential are highlighted and prospective source kitchens are identified. Accumulations of migrated hydrocarbons are recognised and migrational pathways from source kitchens to reservoir are deduced from the available data. The timing of hydrocarbon generation in the source kitchen is determined by extrapolating the burial history models based upon the analysed well sections into the (undrilled) basinal areas. The fully integrated model of the basin will therefore show the areas of mature source rocks, prospective reservoir facies and the development of maturity during the evolution of the basin.
Detailed analyses of hydrocarbons recovered from a field can be used to determine lateral and vertical reservoir continuity. The same analyses will also determine if there has been a leakage due to casing failure or to an unforeseen movement of hydrocarbons from down dip as a result of production. Mixing of oils or of oils and gases associated with separate phases of migration can be detected using analyses employed to characterise and correlate crude oils.
We specialise in……..
- Evaluating the stratigraphic and regional distribution of potential source rock horizons
- Classifying source rock type with respect to depositional environment
- Evaluating source rock potential
- Thermal maturation history
- Burial history modelling
- Defining phases of hydrocarbon generation, migration, accumulation and alteration
- Hydrocarbon occurrences and analysis
- Carbon dioxide/non-hydrocarbon gas occurrences
- Detailed single well evaluations to multi-well regional projects
We also provide training courses in petroleum geochemistry and its application to petroleum exploration. These courses can be held either at our offices in the UK and Singapore, or at a client's office, and are generally of one or two days duration. Details of the course contents are discussed with the client prior to commencement so as to ensure a successful and meaningful programme. Similar programmes are run by JMJ Petroleum for post-graduate students at leading universities in the United Kingdom.
The Importance of the Tectonic and Structural Model on Source Rock
Distribution and Quality – SE Asia as an example
Below is a brief summary of the most salient points on understanding lacustrine source rock systems in SE Asia and highlights the importance of rigorously defining the tectonic/structural framework and tectonostratigraphic history of the basin(s) of interest.
Commercially significant lacustrine source rock systems require the presence of large, long-lived lakes of tectonic (most often extensional) origin; however, they need to have developed in climatic conditions where precipitation exceeds evaporation. In the Gulf of Thailand, for instance, switches in rift polarity along the length of the rift system and, in turn, the ‘Position of Rift Shoulder Uplift', may have not only controlled sediment supply into the depocentre, but depending on the prevailing climatic conditions may have, ultimately, controlled whether that depocentre received the necessary runoff to exceed rates of evaporation or not. In these lacustrine source rock systems, three primary factors control source rock potential (distribution) and quality:
- Primary productivity level, determined by palaeo-latitudinal position of the lacustrine rift system, turbidity and the availability of nutrient;
- Organic matter preservation potential;
- Matrix sedimentation rate controls the dilution (‘pollution’) of preserved organic matter. At low sedimentation rates, under oxic conditions, a positive correlation between sedimentation rate and organic carbon content is observed. Thus, explaining why, in many deltaic and evaporitic settings, organic enrichment is typically low due to inorganic dilution by the sediment matrix.
It is therefore essential to understand the timing of hinterland uplift and erosion, with respect to the ‘Timing of Rift Development’, and where sediment could be entering the extensional rift system and potentially diluting its lacustrine source rocks.
In summary, we obviously want to identify areas where both productivity and preservation potential are maximised and sedimentation rate is minimised. ‘Basin Dynamics’ and the ‘Inclination of the Bounding Faults’ is important here, as a means of understanding the evolutionary cycle of the basin/depocentre in terms of rates of subsidence and available ‘Accommodation Space’ versus relative sedimentation (infill) rate and its influence on source rock development. Three end-member scenarios are envisaged:
- Sedimentation rate exceeds subsidence (accommodation space) leading to marsh and swamp environments dominating, with the possibility of shallow lakes, resulting in much of the organic matter contained within coaly sediments, where preserved;
- Subsidence keeps pace with sedimentation rate, resulting in alluvial and fluvial conditions dominating. The consequence is the production of relatively low concentrations of organic matter (typically < 1.5%) of principally Type III, which is poorly preserved;
- ‘Subsidence Exceeds Sedimentation’ – the best case scenario – resulting in deep lake development and, if suboxic to anoxic conditions prevail, excellent source rocks with high concentrations of organic matter content (which may exceed 10%) of either Type I or II.
The width/depth ratio (‘Overall Accommodation Space’) is also important as it controls the lake’s mixing potential, playing a role in both productivity (nutrient re-supply) and preservation (water column stratification). The timing (initial onset) and duration of rifting – ‘Geotectonic History’ – is key to understand, as oil-prone source rocks tend, in general, to occur best in the upper section of the lacustrine sequence, prior to the final in-filling phase of the depocentre. It is therefore likely that spatial variations in source rock quality reflect differences in the subsidence and in-filling histories of different depocentres (sub-basins) within a larger basin. Therefore, a detailed ‘Tectonostratigraphic Template’, based on seismic and well information, that illustrates these differences, for example, across and along the length of the Gulf of Thailand Rift System, would be extremely useful in terms of providing confidence in predicting which scenario fits best with the data available.
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