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<jats:p>More than twenty pinnacle reefs have been discovered in the southeast of Ajdabiya Trough within the Paleocene carbonate sediments, most of which are oil-bearing. However, detailed reservoir characterization and conditions governing oil fill-up in this reef remained unresolved. The major faults provide paths for significant vertical movement of fluids at the edges of the Intisar reef reservoirs. At the same time, the ongoing karst-solution collapse also creates vertical zones for fluids encroachment both outside of and within the productive area of the Intisar reef reservoirs. The seismic data shows numerous karst-collapse features up to 300 m in diameter which developed shortly after the final drowning of Intisar ‘B’ and ‘C’ reefs. These karst-collapse features may be the main contributing factor to the escape of hydrocarbons within these reefs, which could explain the high-water cuts in the Intisar ‘B’ and ‘C’ reefs. On the other hand, the porosity of the southeastern part of the Intisar ‘A’ reef was significantly improved by fracturing and dissolution, where faults associated with fractures are most common in this part of this reef.</jats:p>

<jats:p>This study develops an innovative workflow to identify discrete lithofacies distributions with respect to the well-log records exploiting two tree-based ensemble learning algorithms: extreme gradient boosting (XGBoost) and adaptive boosting (AdaBoost). In the next step, the predicted discrete lithofacies distribution is further assessed with well-log data using an XGBoost regression to predict reservoir permeability. The input well logging records are gamma ray, neutron porosity, bulk density, compressional slowness and deep and shallow resistivity. These data originate in a carbonate reservoir at the Mishrif basin of southern Iraq's oil field. To achieve solid prediction of lithofacies permeability, random subsampling cross-validation was applied to the originated dataset to formulate two subsets, training for model tuning and testing for prediction of subsets that are not observed during model training. The values of total correct percentage (TCP) of lithofacies predictions for the entire dataset and testing subset were 98% and 93% by the XGBoost algorithm; and 97% and 89% using the AdaBoost classifier, respectively. The XGBoost predictive models led to attain the least uncertain lithofacies and permeability records of the cored data. For further validation, the predicted lithofacies and reservoir permeability were then compared with the porosity-permeability values derived from the Nuclear-Magnetic Resonance (NMR) log, the secondary porosity of the Full-bore Micro Imager (FMI) and the production contribution from the Production-Logging Tool (PLT). Therefore, it is believed that the XGBoost model is capable of making accurate predictions of lithofacies and permeability for the same well's non-cored intervals and other non-cored wells in the investigated reservoir.</jats:p>

<jats:p> Previous basin modelling of the Faroe–Shetland Basin (FSB, offshore UK) has suggested mid-Cretaceous petroleum generation, which predates the deposition of the working Paleogene reservoirs and traps. To justify the time discrepancy between generation, reservoir, and trap formation, factors such as intermediary accumulations and overpressure have been invoked. However, across much of the FSB, the Cretaceous sequences that overly the Kimmeridgian source rock are heavily intruded by Paleogene-aged intrusions. Recent modelling has shown that the emplacement of the intrusions, coupled with lower radiogenic heat production from underlying basement, leads to estimates of petroleum generation occurring up to 40 myr more recently than suggested by previous models. In this work, we seek to better understand the role that igneous intrusions have exerted on petroleum generation and migration in the FSB. Models with varying thicknesses of Paleogene intrusions are compared with those that consider the Cretaceous sequence as purely sedimentary (i.e. similar to assumptions in previous modelling). The estimated times of petroleum generation are compared with geochronological constraints on the ages of oils (i.e. <jats:italic>c</jats:italic> . 90–68 Ma) along with the deposition and formation of other petroleum system elements. By considering only the effect of igneous intrusions, the expulsion onset from the source rock is retarded by up to 12 myr. In addition, our models show the impact of the intrusions on petroleum saturation and migration, suggesting that intrusions have potentially compartmentalized the basin, trapping petroleum beneath or within the sill complex. Finally, our findings suggest that basin models in regions impacted by significant magmatism need to consider the impact of intrusions to more accurately constrain both petroleum generation and migration. </jats:p> <jats:p content-type="thematic-collection"> <jats:bold>Thematic collection:</jats:bold> This article is part of the New learning from exploration and development in the UKCS Atlantic Margin collection available at: <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://www.lyellcollection.org/topic/collections/new-learning-from-exploration-and-development-in-the-ukcs-atlantic-margin">https://www.lyellcollection.org/topic/collections/new-learning-from-exploration-and-development-in-the-ukcs-atlantic-margin</jats:ext-link> </jats:p>