Predicting oil production from chalk reservoirs relies on quantifying contributions from fracture and matrix porosity, which change during compaction. Cl isotopes in water characterise fluid transport processes. Chalk matrix microporosity and fractures will give different values. We will combine two novel methods, trace water extraction from dry oil and Cl isotopes to characterise porosity from produced fluid. High pressure lab. experiments carrying fracture/matrix porosity in cores will give characteristic brine geochemistry related to poroperm to calibrate field values. We will compare fluid derived porosity regime with values measures on field core. Porosity changes from geochemistry will be compared with compaction in the field.

The M2M Thematic Programme funded 17 scientific investigation projects leading to more unified physical understanding of fluid flow distributions in heterogeneous rock. The programme focused on developing an understanding of the relationships between measured and modelled subsurface fluid flows spanning the range of spatial and temporal scales relevant to fluid resource management. The programme was motivated by the growing recognition that assumptions of uniformity at certain scales are inadequate for extrapolating fluid behaviour both in time and space. Research spanning a wide spectrum of observation and simulation scales was undertaken by the programme which can be divided into four themes: (1) understanding the natural processes which lead to scaling relationships between size and magnitude of rock and flow heterogeneity; (2) quantification of essential fluid flow properties and their spatial pattern from measurements;(3) identification of appropriate statistical models and scaling laws describing rock property heterogeneity and fluid-rock interactions in geological media;(4) understanding the relationships between rock property distributions and flow model parameter distributions.

Stability of a reactive front in a heterogeneous porous medium characterised by a statistical description of a permeability and/or reactivity will be studied. Stochastic partial differential equations will be formulated. The feasibility of solving these stochastic differential equations will be evaluated in this proof of concept proposal, and the expected values and variances for the growth rate and wavelength of the disturbances determined as a function of input parameters. The results will have significant impact on areas such as reactive diagenesis in oil reservoirs and acid treatments of well bores. The investigators will interact with Mobil Tec Co., who are partially matching the proof of concept grant.

The project will develop and explore the application of scaling methods to strongly heterogeneous flow fields; investigate the loss and retention of information by scaling over large space and long time scale ranges; and, define the dependence between large space/long time scale migration behaviour and the underlying geological model. High resolution, highly accurate flow and transport simulation data sets for a large number of realisations possessing the high variance and strong textures observed in actual geological systems using alternative geological simulators will be used to test upscaling approaches reported in the physical sciences literature and to identify improving upscaling laws where the existing laws are inadequate.

This proposal is to test the hypothesis that secondary (crack) porosity can be treated as a scaling problem in both fracture and fluid percolation theory. This will be achieved by measurements of elastic, transport and mechanical properties on rock samples with known and controlled crack densities (crack porosities) that span the percolation threshold under a wide range of stress conditions. The measured data will be used to calibrate and validate generic models for fluid and fracture percolation that can then be upscaled to predict permeability at the reservoir scale from wireline logs.

Coupled (mechanical-hydraulic) numerical models based on the distinct element method will be used to investigate the behaviour of fluid flow in fractured rock-masses under stress. Flow localization is predicted at some critical stress; parameters affecting this localization will be investigated. Flow in the vicinity of boreholes and by grain infiltration will be simulated. The models will be tested against field observations and hydraulic tests in boreholes.

Reservoir quality in hydrocarbon reservoir sandstones can be greatly influenced by mineral cementation or dissolution. This can change porosity by 50% and permeability by 105. Such processes were partly controlled by palaeo-hydrogeology. The micro-isotopic and micro-geochemical composition within cements holds a detailed zonation record of palaeo-hydrogeology, which can now be investigated by new micro-scale analytical technology. We will combine conservative tracers and palaeopressures from fluid inclusions with natural isotopic tracers measured by ion and laser microbeam instruments. Statistically based sampling will enable reliable up-scaling to calibrate blocks in basin-scale computer models. This will integrate microanalysis with basin architecture. Study sites are selected to resolve conflicting interpretations of characteristics cementation processes.

This project will use the techniques of stereolithography and PIV directly to measure the fluid velocity field in complex, 2D, geologically realistic media with multi-scaled heterogeneities. The resulting velocity fields will be published widely and will provide an invaluable resource for the validation of models of fluid flow in complex geometries for which validation ID presently impossible. Three specific studies will also be undertaken; a) a detailed investigation of the non-linear interaction between matrix and fracture flow, b) a study of the scaling laws in the region of the percolation threshold in the presence of fractal fracture populations and significant matrix permeability and c) an examination of the scaling of the velocity flow field and how this reflects material scaling with a view to identifying potential rules for upscaling of fluid simulations.

The aim of the proposed project is to study evolution in the spatial characteristic of coupled flow and porosity development in heterogeneous porous media. We will develop a modelling engine and methodologies to generate porosity templates for use in flow and transport models of fractured aquifers. Although the primary motivation for this study is to enhance our ability to predict flow and contaminant transport in vulnerable fractured aquifers, such as the chalk, the approach is generic and we foresee a wide range of scenarios where the model may be applied. The work has three specific objectives: 1) to produce a generic model of porosity development, 2) to investigate percolation, scaling and self-organisation phenomena in porosity development due to flow, and 3) to model pore structure and flow histories for a range of natural and anthropogenic problems.

This project is designed to integrate geological structural characterisation of fault zones with numerical modelling of flow behaviour at different scales. We will develop a 3D flow simulator which can model the impact of geological heterogeneities (clustered fault / fracture arrays) under different stress conditions on fluid flow. The project is collaboration between a structural geology research group (the rock deformation research group), an applied mathematics group (the centre for computational fluid dynamics) and a series of industrial partners (Arco, BP, Shell and Midland Valley).