Exploration Insights September 2019 | Page 28

28 | Halliburton Landmark Exploration Handbook | 29 To assess plays easily, defining data can be tabulated alongside the diagrammatic depiction of the play cross section. This also aids comparison at the play level in each basin and across different play cross sections. Assessing Petroleum Potential and Critical Risks Play cross sections provide insight into some of the factors that determine the success or failure of a play, helping to highlight those plays that require further evaluation. On a Neftex Play Cross Section, an assessment of the likely hydrocarbon phase and critical risk for each play is shown in a table. The critical risk field is populated for both unproven and proven plays, highlighting any factors that may heavily influence the success of similar future plays. Risks will vary for each play and may include: » » The presence or absence of play elements and their relationship to each other » » The thickness of source, reservoir, and seal » » The quality of play elements, assessed through metrics, such as TOC, porosity, and permeability » » Migration pathways and features that may help (faults) or hinder (carbonate baffles) flow » » Potential for trap development, both structural and stratigraphic » » The potential closure and breach of traps (in 2D only) » » The potential maturity and charge of the system A Additional information for each play can also be recorded, including the critical exploration risk, likely hydrocarbon phase, trap size, or exploration status. Assessment of these factors can help to guide understanding of the play concepts and their hydrocarbon prospectivity. Understanding these criteria provides a first pass screening process of the play potential in the area. This can be assessed through the number of potential plays listed, how many are proven and how many are frontier, and the likely hydrocarbon phase and critical exploration risks. While this assessment provides an indication of hydrocarbon potential, it is important to note that the plays illustrated on a play cross section are often conceptual and do not allude to volumes. They simply represent reservoir, charge, seal, and trap combinations that may work, have worked here, or have worked in analogous basins. Data Uncertainties Understanding how a play cross section is constructed allows for an assessment of data uncertainty. This should be considered if using a published play cross section or while creating your own. Knowing where the diagram is data-driven enables validation, and it can help increase confidence in the assessment of the plays it represents. The amount of data incorporated during the construction of a play cross section varies depending on the exploration maturity of the basin (whether data are available) and the quality of the data. These data can be validated in isolation, but also indicate the reliability of the inferred insight. Where data constraint is poor, it is important to consider what model has been applied to make the predictions and interpretations of the geology. This may be a geodynamic or sequence stratigraphic model, or it may involve the use of analogues. In each case, the applicability of the model and its resultant interpretation needs to be assessed. “ Play cross sections provide insight into some of the factors that determine the success or failure of a play ” Play cross sections are built as schematic representations of the area and, therefore, might not have a detailed enough resolution to truly assess certain play elements, such as composition and trap geometries. OGT Onshore Shallow Ultra deep Deep BOW B BO W L L L L L OGT L L L L Sea Level Mature Fairway Exploiting Differently © 2019 Halliburton such as age (whether it is sequence stratigraphic, by stage, or by biozone) or reservoir type (e.g. carbonate or clastic). The classification scheme should be defined by the needs of the user to best identify trends and groupings in their data. Neftex plays are classified by reservoir age, reservoir depositional environment, and the trap type, for example: Aptian shallow marine carbonates in thrust anticlines. L L L L L Broadening Geography Deepening Stratigraphy L L L L L L L L L L BOW B OW L L L L L L L L © 2019 Halliburton © 2019 Halliburton Figure 7 > The effect of lithology on geothermal gradients. A) The high thermal conductivity of salt changes the geothermal gradient. B) Volcanics have a local effect and increase the geothermal gradient. Figure 8 > The predictive power of play cross sections. By understanding the areas with data control and validation of working petroleum systems, the play cross sections can be predictive. Generation of new play concepts comes from the extension of existing plays from within the basin or analogous basins. These may extend plays deeper, laterally, or distally. The play cross section can also help to generate new play ideas through the suggestion of untested source rock, reservoir, seal, and trap combinations.