Prediction of reservoir properties from processes and architecture in deep-water clastic systems

Abstract

Deep-water depositional systems are sculpted, and built from the deposits of, discrete flow-types and depositional processes. Different flow processes govern the interactions with substrate, and control whether flows are depositional or erosional, the architecture of the geobodies, and the grain-scale texture of any deposit. The interplay of these variables results in a wide-range of heterogeneities at different scales in deep-water systems. These heterogeneities, from grain-scale, to bed-scale, to architectural-element-scale, each exert strong controls on reservoir quality distribution and performance. Therefore, understanding where these heterogeneities develop, how they develop, and how they impact fluid flow important for reservoir quality prediction in the subsurface. Here, multiple methods including: 1) petrographic thin section analysis; 2) sedimentary logging; 3) architectural panel analysis; and 4) reservoir modelling, are used to document the distribution and effects of each scale of heterogeneity. Datasets utilised include: outcrop studies of the Tanqua Depocentre, South Africa, and the Jaca Basin, Spain; and core-plug and bed-type data from the X Formation, North Sea. Key outcomes of the study include: 1) the spatial variability of grain-scale texture, and its associated effects on reservoir quality, is quantified for the first time in lobe and channel-fill deposits. Axial positions are shown to have better reservoir potential than marginal or fringe positions due to an abundance of coarser-grained, cleaner, high-density turbidites; 2) bed-scale heterogeneities, and bed-types with discrete grain-scale textures, are demonstrated to exert strong controls on connectivity and permeability in reservoir models. These heterogeneities strongly impact permeability in models of discrete sub-environments of a submarine lobe deposit. Axial positions exhibit the highest permeabilities due to an abundance of structureless sandstone, whereas fringe and off-axis positions are characterised by structured sandstones, and exhibit low permeabilities. Realisations of a distal lobe finger reveal high permeabilities, and challenge the notion that the distal lobe fringe is all poor-reservoir quality; 3) architecture and facies distribution of a submarine channel-fill are characterised in three dimensions, and reveal consistent lateral axial to margin trends, whereas longitudinal changes in facies are less-predictable. Characterisation of channel-base-deposits and their distribution demonstrate challenges in their identification, and implications for reservoir compartmentalisation; 4) variable flow confinement and flow deflection are suggested to influence lobe stacking patterns and depositional processes, increasing heterogeneity at multiple scales adjacent basin margins, and therefore reservoir quality distribution.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stephen Flint (Supervisor)