AAPG Middle East Geoscience Technology Workshop, Integrated Emerging Exploration Concepts

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Quantifying Seal Effectiveness, Seal Effectiveness Timing, HC Column Height, % Trap Fill, Timing Risk using Petroleum System 1D Models for Leads and Prospects


Petroleum System Timing is a key factor not always quantified, and therefore, not properly Risked for Leads and Prospects. Seal Effectiveness, Seal Effectiveness Timing, HC Column Height, % Trap Fill, and therefore, Timing Risk can be determined using Petroleum System 1D Models for Leads and Prospects. Petroleum System 1D modeling is an easy-to-use geologist’s tool for assessing timing risk and hydrocarbon column height for Leads and Prospects. But most geologists have forgotten about petroleum system modeling once they are at the prospect level…and therefore, just take a guess at these essential factors in calculating volumetric and prospect risk. Seal presence is not seal effectiveness. Seal effectiveness is controlled by the lithology at the very base of the seal section and how much it is compacted. A thick seal section with no compaction is not a seal. The timing of the seal effectiveness must be related to the timing of the charge from the specific kitchens that feed that closure. Discoveries in the area do not tell you more than there is good source in the area that can produce hydrocarbons. It is the maturity timing of the specific kitchen areas that feed each structure that determines that structure’s potential. In a 3D petroleum system model, the seal capacity is determined for each seal relating to the facies that are at the base of the seal. Because the 3D PS model is dynamic, it tracks the seal effectiveness through time and relates it to the timing any hydrocarbons that migrate to the structure. The trap (structure plus seal) can hold larger columns as the seal effectiveness changes through time. It determines what the hydrocarbon column might be and the % Trap Fill. These are essential inputs into prospect volumetrics, but assessors seldom think to refer to the “basin” model once they are doing prospect volumetrics. They guess instead of using this science. Analogues are just a way to fool yourself that your guesses might be right. With or without a 3D model, Petroleum System 1D models can be run in sets to look at each structure and determine its top seal effectiveness and effectiveness timing and the generation and expulsion timing for the all the kitchens that feed that structure. This includes the type of hydrocarbon that might be generated. The Time Trend plots can display output from all the 1D models in the set. By displaying the Transformation Ratio from all the kitchens, the start of generation (TRall > 0), expulsion (TRall > 12 – 20 %), peak hydrocarbon output (TRall = 50%), and final burnout (TRall = 100%) can be determined. By displaying the seal capacity (MPa) at the top of the structure, the time when the structure became a trap capable of holding a significant column can be determined. Using the maximum seal capacity, the hydrocarbon column height can be calculated and the % Trap fill for the prospect volumetrics can be calculated. Which is much better than a guess (analogue)! All of these relationships can be displayed on a Petroleum Systems Events chart which show how well the timing relationships work for each prospect. Rather than a generalized PS Events chart, a chart is created for each prospect to demonstrate the reasons for the estimate for Timing risk.