Pore morphology and the characterisation of North Sea sandstones

Within the oil and gas industry it is of the utmost importance to determine the value of a hydrocarbon accumulation. Key to this process is the prediction of reservoir flow and performance. Measurements on core are the main source of information that underpin this crucial prediction; however core is not always available and it is necessary to find another means to estimate the required flow properties.;Inspection of core data often reveals the presence of a simple relationship between the core porosity and the permeability to gas. Where this is the case, it is common practice to establish a relationship and then use estimates of porosity from wireline logs to predict permeability. However, for the reservoir examined in this thesis, like many others, this porosity-permeability relationship is neither linear, nor straight-forward.;A plug porosity-permeability relationship for this reservoir was derived from the analysis of 199 sandstone plugs. In addition 63 of these plugs have image analysis data; the end-trims of these plugs were impregnated, sectioned and polished. Back-scattered electron microscope images at both high (x150) and low (x30) magnifications were taken, captured as 256 grey scales and numerically analysed. This analysis enabled the pore geometry to be quantified.;The images data led to an improved understanding of the controls on permeability and porosity. This understanding was achieved by the demonstration that micro-porosity is an ineffective porosity in terms of fluid flow. Micro-porosity is identified as pores <13 m2 and mostly occurs within the clay (defined as the grey scale range 50-170 on the SEM images). Image porosity was calculated and observed to be less than plug porosity and has a stronger linear relationship with permeability; this is a result of micro-porosity being included in the measurement of plug porosity but not in the image porosity calculation. A non-linear relationship between gas permeability and mean pressure in the calculation of Klinkenberg permeability is present; a possible explanation for this observation is given.