| Abstract/Description or Keywords |
Thin section petrography was conducted on forty-four (44, see Table 1) samples from the OW-11-01-Nanaimo OBS well 390, to determine their mineralogical, textural, diagenetic and reservoir characteristics. Work was focused on pore systems and processes affecting the porosity evolution. Various diagenetic features have affected the reservoir quality to varying degrees, both creating and destroying porosity. The original intergranular pores are blocked by matrix clay and further reduced by early chlorite lining, quartz overgrowth, feldspar overgrowth and compaction, therefore no original intergranular pores were observed in any sample. Later stage dissolution produced secondary intergranular pores and improved the reservoir quality of Nanaimo Group sandstones to some degree. The formation of pyrite, calcite cement and organic matter emplacement locally occludes secondary pore spaces, all sandstone samples show very low to low visible porosity (trace to 2-3%). The porosity types of the Nanaimo Group sandstones can be generalized as: secondary porosity (sp), microporosity (mp) and microfractures. Secondary porosity (as a result of feldspar dissolution) is the major pore type in the Nanaimo sandstones. Microporosity is abundant and is extensive within the clay matrix, leached feldspars, chert, and rock fragments (volcanic, plutonic and metomorphic rock fragments) and has little contribution to reservoir quality due to the very smaller pore size. |
