Fully Integrated Modelling of Subsurface, Remote Sensing and Outcrop Geology; Prospect Generation in the Paleozoic of the Ahnet Basin Algeria

Abstract

The fully integrated modelling of subsurface seismic and well data with outcropping surface geological data is a challenge in which the application of modern technologies which involves the standardisation of datasets on different scales and from different sources plays a key role. In this paper we present an example of the Paleozoic of the Ahnet Basin in Algeria where a prospect generation exercise was undertaken integrating data from 2d and 3d seismic volumes, logs and core data from previously drilled wells, maps of outcropping geology, and high-resolution remote sensing datasets. The geology of the area is well known from previous studies on both surface geology and well data, and comprises a Paleozoic series unconformably resting on infra-Cambrian relative basement, and made up of clastic sedimentary series with intercalation of limestone sediments ranging from Cambrian to Devonian Age, which comprise various gas bearing tight reservoirs some of which producing in this part of the Basin. These are present in anticlinal structures of Hercynian Age which are partly eroded and covered by Cretaceous bioclastic limestones. The anticlines show a deformational history reflecting an interference of differently oriented Hercynian transpressional deformation patterns overprinted by later stage, Alpine reactivations. Our integrated geological analyses permitted to propose a new updated view on the geological history of the area. This includes the reconstruction of the structural deformation of the Hercynian anticlines, and the reconstruction of the post-Hercynian geological evolution including structural reactivation, showing tilting and upheaval of the area in Alpine and Recent times. An extensive interpretation of outcropping geological structures was performed using high resolution satellite images and specific image processing. This was calibrated with available high-quality geological maps and some later additional limited geological surveys. Detailed well log correlations and seismic interpretation 2d and 3d seismic data provided a detailed framework of subsurface structures. The datasets on surface vand subsurface originally coming from different digital sources were integrated in one uniform interpretation environment using best practice standardization which permitted to drive the seismic interpretation and depth modelling, by carefully calibration with outcropping features such as bedding dip, fault trends and fold axis trends. Applying regional velocity modelling this permitted to correctly map the geological structures and prospects in the area, and perform an articulated exercise of Prospective and Contingent Resources estimates. The application of an integrated geoscientific workflow deploying up-to-date technologies which integrate GIS with a surface-subsurface 3d modelling space shows the validity of new developments of the 4th Industrial Revolution in the planning of E&P Prospect evaluation.