Confinement effects on the physical properties of shale oil and gas
Creators: name: Videnberg, Theodor
Publisher: name: Imperial College London
Year: 2018

description: BP, EIA and other organisations estimate that huge amounts of hydrocarbons are stored in shale and tight-oil reservoirs. With the improvement of drilling techniques, multi-stage hydraulic fracturing and geological characterization, hydrocarbon production (particularly in the USA) and research into shale reservoirs has intensified. A particular feature of those reservoirs is their exceptionally low permeability and pore diameters down to the nano-meter range, a region where the pore diameter sizes of the porous media approach the dimensions of the molecular fluid sizes. At those conditions, previous experimental, modelling and analytical work has indicated that confinement effects can be present, which modify the fluid properties from bulk (macroscopic) ones. Confinement has been observed to have affected critical temperatures, possibly critical pressures, phase transition lines, diffusion coefficients and so-forth. A particular problem of the experimental techniques, which have been used in the past to study confinement, is that they are either performed at low temperature and/or low pressures, conditions which are not applicable for shale reservoirs. In this thesis a new methodology is introduced to study confinement and pore properties at elevated pressures and temperatures. The methodology is based on a material balance approach, which has been tested on the systems of (methane + pentane + SBA-15) and (methane + decane + SBA-15) at temperatures on the range (325 - 400) K and pressures up to about 24 MPa. The results of those measurements and the methodology will be introduced in the thesis, as well as relevant information on the experimental setup used (synthetic non-visual method according to the Dohrn classification). Errors and the uncertainty analysis will also be discussed. The uncertainty analysis is performed with a Monte Carlo simulation that captures the entire experiment and all possible uncertainties. The method of implementation of the Type A and Type B uncertainties is introduced and discussed. Additionally, a new experimental apparatus is designed which is based on Raman spectroscopy, employing a visual cell and using an analytical technique. Equipment design, relevant calibrations and some measurements with the (methane + pentane + SBA-15) - system with that particular setup will be presented. I also present modelling work on confinement as part of the thesis. This includes the analytical derivation of a confined equation of state for the hard-sphere and for the square-well fluids, employing a van der Waals-type approach in the limit of low density. In another step, the modification of the Peng-Robinson 1978 equation of state (EoS) to account for confinement is presented. The implementation of the confined cubic equation of state into a programming environment is discussed. The advantages, pitfalls and assumptions of these approaches are addressed. The work is relevant for hydrocarbon exploration and production of shale reservoirs, as it presents a new route for the measurement of confinement effects at elevated pT conditions. Methods to improve the experimental setup and decrease the uncertainties are also discussed. The thesis also shows that there are differences in the composition and pore density of confined fluids as compared to the bulk state, which has direct significance for hydrocarbon-in-place estimates and multi-billion dollar management decisions made in the petroleum industry.