Exploration Insights September 2019 | Page 22

Exploration Handbook | 23 » » To aid frontier play analysis by providing a framework for assessing analogue basins and play types » » To help evaluate the likely generation of hydrocarbons through burial depth of source rocks and an assessment of thresholds, such as the oil and gas windows By: Emily Firth » » As an input for basin modeling by providing information on basin evolution and fill, including the depth of burial, thickness, and lithology of play elements WHAT ARE PLAY CROSS SECTIONS? A play cross section, or schematic play concept diagram, is a simplified geological cross section that illustrates the stratigraphic and structural context of one or several plays along a particular transect. Resolution can vary, but representation is typically on the basin, field, or prospect scale. The Z-axis is presented as either depth or seismically derived two-way travel time. Play cross sections can be depicted as simplistic cartoons, derived from a basic regional understanding, in order to illustrate the presence or relationship of certain play elements. More detailed transects are typically based on structures identified from seismic lines or regional cross sections. A detailed depiction of the stratigraphy is made from well data, chronostratigraphic charts, and gross depositional environment (GDE) maps. An example of a highly simplified Neftex ® Insights Play Cross Section can be seen in Figure 1, illustrating play concepts within Cyprus and Lebanon. » » To illustrate sequence stratigraphic concepts and highlight the tectono-stratigraphic evolution, aiding prediction of stratigraphy where data are sparse “Play cross sections help evaluate the likely generation of hydrocarbons through burial depth of source rocks and an assessment of thresholds, such as the oil and gas windows” BUILDING A PLAY CROSS SECTION Play cross sections are built from a wide array of geological data (Figure 2). There are no widely accepted standards for producing play cross sections, but some of the data and concepts that can be used in their construction are described in the following sections. Basin Familiarization East I C T UR A L O R U S T S M I C S E C T I O R N E I L L S A N W E A T I G R D R A P T H O S PO S I T IO S D E O S N M E N T (G N A R I R O D V N Pli Pl Miocene G Oli Eocene Pale Late Cretaceous Neogene Q IN Paleogene Early Cretaceous M OD E L B Late Jurassic Speculative source S? Cretaceous R Reservoir S Source I N A S Predominantly deep-marine carbonates Basement Salt Predominantly shallow-marine carbonates Predominantly deep-marine mudstones Sand-rich clastic intervals The first step is to familiarize yourself with the area of interest. What exploration has occurred in the area, what was targeted, and was there any success or failure? What data are available to improve the understanding of the geology, and can they be used to construct the play cross section? This will help when assessing what features the play cross section should depict (i.e. dip or strike line) and the resolution of the diagram, both geographically (e.g. basin, field, or lead) and stratigraphically (e.g. bulk lithology or high-resolution facies). West » » To provide a framework for capturing available data and key uncertainties within a basin Figure 1 > A highly simplified example of a Neftex Insights Play Cross Section from Cyprus and Lebanon. ® APPLICATIONS OF PLAY CROSS SECTIONS J10 LST–J20 TST (181Ma) » » To show the geographic and subsurface distribution of tested and untested plays J80 TST (159.8 Ma) 50 Provides an understanding of thermal regime » » To illustrate play concepts as simple reservoir, charge, seal, and trap combinations D Y N A MIC M O D Provides age and lithological constraint Provides the structural framework P E R T I E P R O S C K I C G E O C H E M A N O N I A FINAL PLAY CROSS SECTION E O Gives insight for infilling stratigraphy » » To highlight the approximate position, stratigraphic thickness, and depth of burial of key play elements 100 Play cross sections have a number of different uses: 150 » » To help determine the prospectivity of an area by capturing proven play information, as well as untested play potential » » To provide rapid familiarization of a basin’s evolution, both structural and stratigraphic » » To provide insight into potential risks associated with untested plays as a first pass assessment on reservoir quality and charge Establishes timing and context of key tectonic events Play Cross Sections — Visualizing Play Concepts Confirms petroleum system elements Figure 2 >The building blocks of a play cross section. The structural framework is provided by a seismic line. The stratigraphy is filled in using well data and an understanding of the regional geology through gross depositional environment (GDE) maps and chronostratigraphic charts. Where available, other data are incorporated to provide further constraint on the interpretation. 22 | Halliburton Landmark