Fluid flow through connected sub-seismic features in mudstone

In the past decade, tight sandstones and shales are increasingly being considered for hydrocarbon production however there are still several scientific and technological obstacles to overcome to ensure unconventional reservoirs are economically viable. Compared with conventional reservoirs, such as permeable sandstone, there is a paucity of basic field research involving mudstone formations, partly due to their susceptibility to erosion making field studies difficult. Other direct applications are radioactive waste disposal and also CO2 storage. A 15 metre thick faulted shale unit, deposited in the distal zone of a submarine fan, was studied to investigate the controls on fluid flow through low permeability clastic rock. Turbidite flows are present within the shale as very thin (1-5mm) fine grained sandstone beds, channels and lenses which would not be picked up by wireline logging. The shale is cut by a series of conjugate faults and an associated fracture network; the faults have a maximum recorded throw of 10m i.e. at the limit of typical industry seismic surveys. Field data show evidence for two distinct flow episodes; carbonate-filled veins and green alteration halos. Flow utilised a subgroup of both the fractures and the more permeable sandstone bands but this flow network varied between flow episodes. Flow modelling shows that the interplay between the structural and depositional features, often averaged out during upscaling processes, acts to significantly increase the connectivity of the flow network emphasising the importance of field statistical characterisation for predicting distributions of such small scale features. Predictions based upon statistical analysis of data from sparsely distributed boreholes are likely to be needed to accurately characterise these sub-seismic flow networks. Key features that controlled permeability enhancement were closely spaced faults creating an interaction zone of high fracture density and networks with fluid flow conduits that connect to multiple other conduits.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2014

Author dc:creator

• McCay, Alistair

DOI

10.48730/fwr3-8k57

Identifier

T13764

OAI identifier oai:identifier

oai:strathclyde:g158bh353