Exploration Insights September 2020 - Page 6

6 | Halliburton Landmark West East Guadalupe Peak Delaware Basin Central Basin Platform Midland Basin Eastern Shelf © 2020 Halliburton B Woodford Stratigraphy Permian Mississippian Late Devonian Ordovician Element and Process Groups Source Rock and Charge Overburden Reservoir Bone Springs/ Spraberry Wolfcamp Barnett Simpson Quality of Petroleum System 0 1 Seal and Trap Preservation Inadequate 0 Processes Elements Bone Springs/Spraberry Simpson Idealised 1 Woodford Wolfcamp A Percentage of basin covered with source rock Source rock thickness Simple burial history of source rock Thick, high-permeability reservoirs Multiple reservoir intervals Multiple seals Effective regional top seal Active charge today Diffusivity of charge system Diverse traps Simple low strain traps Large areal coverage of traps Structural reactivation Remobilised hydrocarbons Minimal alteration/degradation Woodford Example © 2020 Halliburton Figure 2> A) Line of section through the Permian Basin showing the architecture of source rocks and their stratigraphic position. B) Example of the schema used to define the holistic petroleum system index of the Woodford Formation petroleum system. Note the system scores poorly on some of the petroleum system processes due to the complex burial history of this formation. Play Analysis database. Figure 2A shows the application of the schema to the Permian Basin in the United States, where the key source intervals form five distinct petroleum systems. The schema was developed from our work on classifying super basins, which you can read about in the May 2018 edition of the Exploration Insights magazine. In the proposed schema, petroleum systems are evaluated on the following criteria (Figure 2B): »» The nature and scale of the defining source rock »» The extent of the charge system »» The range of proven or potential reservoirs and seals that do, or could, store hydrocarbons over geological timescales »» The range of proven or potential traps that do, or could, retain hydrocarbons over geological timescales Under this schema, a play (or an individual reservoir or trap) can be assessed as being part of more than one petroleum system, where charge from more than one source rocks is possible. It should also be noted that within this assessment, a petroleum system has the potential to incorporate either one or several proven and/or unproven plays. If a petroleum system has one proven play and many unproven plays, it is still classified as a “proven” petroleum system. ENABLING OBJECTIVE COMPARISON Having defined a set of petroleum systems globally, the next step was to create an analytical schema focused on the factors that regionally enhance the quality of petroleum system elements and processes. For example, for reservoirs these factors include the occurrence of stacked pay levels with thick, high-permeability reservoirs. For source rocks, the preferred characteristics include the occurrence of basinwide, thick, organic-rich intervals. To enable more objective comparison, a numerical index score between zero and one was assigned to each characteristic, based on a series of threshold values. Table 1 shows an example