CAN OIL EMPLACEMENT PREVENT QUARTZ CEMENTATION IN SANDSTONES

In the current debate on the ability of oil emplacement to halt quartz cementation in sandstone oil reservoirs, this paper supports a 'yes, it can' answer. Although we find some of the empirical data (petroleum fluid inclusion abundances, quartz-depth trends) to be inconclusive, we have made progress in this debate by examining theoretical controls for three end-member quartz cementation scenarios. (1) Silica externa lly sourced via advection. Oil emplacement must halt quartz cementatio n because of the associated massive reduction in relative permeability to water. (2) Silica supplied internally, water-wet reservoir. Quartz cementation will be inhibited because the rate of diffusion will be r educed by orders of magnitude, making diffusion the rate controlling s tep. The degree of inhibition will depend on rock fabric and oil satur ation; at very high oil saturations quartz cementation could effective ly cease. (3) Silica supplied internally, oil-wet reservoir. Quartz ce mentation will be halted as water cannot access to grain surfaces.