Geological and Geostatistical Models of Qusaiba Shale: High Resolution Outcrop Analog from Central Saudi Arabia

摘要

Qusaiba shale represents an important source rocks and reservoir target for shale gas in Saudi Arabia. Geological heterogeneity within Qusaiba represent a challenge for characterization, exploration and development. A detailed study has been carried out to describe and characterize Qusaiba shale in central Saudi Arabia using high-resolution outcrop analog from central Saudi Arabia. Here we describe measure and model the spatial distribution of lithofacies, porosity and geomechanical properties at outcrop scale. The aims of this study are to describe the lithofacies, paleoenvironments and to reconstruct 3D high resolution geological and geostatistical model for Qusaiba Formation. Excellently exposed Qusaiba Formation outcrops in central and northern Saudi Arabia provide good outcrop analog for the subsurface equivalent of Qusaiba succession These outcrops suit quite well for examining and evaluating geological heterogeneity (sedimentological, stratigraphic, structural and geomechanical properties). All these aspects might all have important impacts on shale reservoir properties and quality and architecture. Outcrop analog studies provides high resolution scales information within interwell spacing where subsurface data and information have some limitations. Integrated approach was followed to observe, measure sedimentologic, stratigraphic properties that supported by laboratory measurements of lithofacies types, porosity, Schmidt hammer values, point load index, P-wave velocity and dynamic Poisson ratio. Based on field and laboratory data a 3D geological and geostatistical properties models have been generated. These lithofacies were deposited in offshore and lower shoreface to middle to the upper shoreface depositional environments. The geological and geostatistical models are capable to capture the lithofacies distribution, cyclic nature of and architecture at outcrop scale.The geostatistical models show the 3D distribution of Qusaiba shale properties including lithofacies, porosity, Schmidt hammer, P-Wave velocity, point load Index and Poisson ratio. Generally, a good correlation is noted between facies vertical and lateral distribution and the other parameters. This agreement on distribution pattern reflect first the depositional control on lithofacies from offshore at the base to upper shore facies at the top as revealed on the three main depositional cycles. That property modeled reflect depositional lithofacies and stratigraphic hierarchy. Variation in values distribution might reflect depositional and post depositional controls. The high-resolution outcrop analog models might provide guides and leads for the prediction of the lithofacies types and porosity distribution. The models are capable to capture the lithofacies distribution, cyclic nature of and architecture at outcrop scale and this might help to understand and predict sedimentary properties and heterogeneity of equivalent lithofacies in the subsurface.