Abstract Thirty-eight mudrock samples from the Cambrian Conasauga Group were analysed by immersion, helium and mercury porosimetry. The data generated from these techniques include effective porosities, pore throat size distributions and sample densities. The purpose of these analyses was to obtain information required to evaluate the capacity of the Conasauga Group mudrock to retard transport of and to store contaminants on the Oak Ridge Reservation (East Tennessee, USA). Results indicate that the three porosities were 9.90±2.61%, 3.8±0.7% and 8.1±4.3% for immersion (φI), mercury (φHg) and helium porosity (φhe), respectively. These values are considerably higher than those previously reported for these rocks (0.1–3.4%). The φHg values are commonly the smallest of the three. Although the three porosities generally show little change with depth, an expected trend as a result of the maximum burial depth of the Conasauga Group of >4 km, a decrease with depth is seen in some of the coreholes for only φI. Furthermore, inconsistencies between the different porosity types provide an insight into the mudrock pore structure and related geochemical characteristics. For example, they indicate the existence of considerable pore space accessed only through <3 nm pore throats and the possibility of meteoric cement having replaced original diagenetic cement for some mudrock samples, which would lead to a possible instability to immersion with contaminated water. These characteristics have significant implications for the evaluation of the mudrock retardation and storage capacity for contaminants, and the design of remediation measures.

Porosity characteristics of Cambrian mudrocks (Oak Ridge, East Tennessee, USA) and their implications for contaminant transport

Thicknesses of adsorbed water layers on sediments from the JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well, Northwest Territories

Differences in petrophysical properties (e.g. porosity and electrical resistivity) were noted between similar rock types from Giant and Con mines in the Yellowknife mining district (Northwest Territories). For example, the time required for resistivity of the rock samples to stabilize after pore-water saturation was considerably longer for Giant mine samples compared to Con mine samples. An exploratory study was initiated to find an explanation for these differences. This involved monitoring the resistivity of water used to immerse samples from the two mines, over a period of 340 hours, after vacuum saturation. Results indicate that considerable differences existed between the resistivity-time curves of the water in which the samples (sericite schist and basalt) from the mines were immersed. The resistivity of the water containing Giant mine samples was consistently higher and required considerably longer time to stabilize, compared to the Con mine samples. These differences are consistent with the differences in the sample porosity and electrical resistivity. 1 Contribution to the 1999-2003 Yellowknife, Canada-Northwest Territories Exploration Science and Technology (EXTECH III) Initiative 1 Résumé : On a relevé des différences dans les propriétés pétrophysiques (p. ex. porosité et résistivité électrique) entre des types de roches semblables provenant des mines Giant et Con dans le district minier de Yellowknife (Territoires du Nord-Ouest). À titre d’exemple, le temps nécessaire pour que la résistivité d’échantillons de roches se stabilise après leur saturation en eau interstitielle s’est révélé considérablement plus long pour les échantillons de la mine Giant que pour les échantillons de la mine Con. Pour expliquer ces différences, on a entrepris une étude exploratoire qui consistait à surveiller la résistivité de l’eau utilisée pour immerger des échantillons provenant des deux mines pendant 340 heures, et ce, après leur saturation sous vide. Les résultats obtenus indiquent des différences marquées dans les courbes de la résistivité en fonction du temps de l’eau d’immersion des échantillons (séricitoschiste et basalte). La résistivité de l’eau contenant des échantillons provenant de la mine Giant était uniformément plus élevée et prenait beaucoup plus de temps à se stabiliser que celle contenant des échantillons de la mine Con. Ces différences concordent avec celles relevées sur la porosité et la résistivité électrique des échantillons.

N Scromeda

Papers

Effect of vacuum-drying and temperature on effective porosity determination for tight rocks