Outcrop-Based Geological Modelling of Fluvio-Deltaic Successions From the Middle Jurassic Ravenscar Group, Yorkshire, NE England

Abstract

Fluvio-deltaic sandstones are significant petroleum reservoirs around the world. Sandstones deposited in these settings are volumetrically important but are often heterogeneous as petroleum reservoirs. Upscaled geological models based on sparse well data and low vertical resolution seismic data commonly lack the facies scale heterogeneity which controls the petrophysical properties. Outcrop analog studies are a methodology for capturing the facies architecture in such systems. The present study has used the well exposed coastal cliff sections of the Middle Jurassic Ravenscar Group in Cleveland Basin, UK to build high resolution three-dimensional geological models.

Data were collected by field observations, LiDAR scanning, and UAV (drone) photogrammetry from ten outcrops along a 40 km long, 30 to 130 m thick section between Kettleness and Yons Nab on the Yorkshire Coast. Sedimentary logs were collected from 29 accessible localities along the outcrop and 27 borehole cores behind the Long Nab outcrop. Well logs from a further 15 boreholes behind the Ravenscar outcrop were also incorporated. LiDAR and drone data were used to build scaled photorealistic virtual outcrops from which sandstone body geometry (e.g., width, thickness), stacking pattern, distribution and average lithofacies were studied. Integrating the fieldwork data, VO data and borehole data, a series of high-resolution three-dimensional geocellular models were built to study the distribution of sandstone bodies and their connectivity.

Virtual Outcrop studies and outcrop reservoir modelling are powerful techniques for the analysis of fluvial architecture as they provide a means to remove the bias that results from studying facies proportions in single vertical sections. The prepared small (3 to 10 km² area) but high resolution (10 m x 10 m x 0.5m cell size) models provided a unique three-dimensional subseismic scale insight into the sandbody geometry, distribution and connectedness. The thin cell size (0.5 m) of the model allowed small-scale facies such as the thin storey surface mudstones, the heterolithic facies within counter point bars and the thin crevasse splay sandsheets to be captured. The study identified the channelbody connectivity through overbank crevasse splays in low N/G delta plain setting. The facies scale geological modelling study improves the understanding of the subsurface heterogeneity and may contribute to enhance the petroleum production.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018