The Origin of Large-Scale Quartz Cementation: Evidence from Large Data Sets and Coupled Heat–Fluid Mass Transport Modelling

Summary

Quartz is the most important porosity destroying cement in sandstone reservoirs. The large petrographic data sets, from 11 intervals from around the world, presented and referenced here, indicate that massive quartz cementation follows a predictable pattern. Cementation occurs in two distinct phases: an early minor phase during which a few percentage of authigenic quartz are precipitated, followed by the relatively abrupt start of massive deep burial cementation which can result in up to 20% reduction in porosity. Massive quartz cementation typically begins at 90 ± 10°C. The relative temperature dependence indicates some form of kinetic control.

Computer modelling indicates that it is not possible to import large quantities of silica into the reservoir. Thus the source of silica for quartz cementation must be derived from within the sandstone or directly adjacent to it. The pattern of cementation strongly suggest sources which have a temperature and, in some cases, a stress dependence. Temperature-dependent silica contributing reactions probably include the dissolution of feldspars, the transformation of smectitic clay to illite and the dissolution of heavy minerals (although only a minor contributor in many circumstances). Pressure dissolution within sandstones and adjacent siltstones also becomes important over the same stress/temperature range, partly because the dissolution of framework grains will increase the stress on the remaining framework grains. Finally, fluid movement within a non-isothermal reservoir promotes redistribution of quartz.