Synchronous oil migration and cementation in sandstone reservoirs demonstrated by quantitative description of diagenesis

Abstract

We present a model that explains the patterns of sandstone burial diagenesis in certain oil reservoirs, in which petroleum migration and burial cementation were synchronous. The coincidence of these two processes controls the chemistry and distribution of major burial cement phases across the field, which in turn controls the distribution of reservoir quality, causing a rapid decline of porosity and permeability with depth. Such a rapid poroperm deterioration is observed in many North Sea sandstone oilfields; we highlight the Magnus Sandstone Member of the Magnus Oilfield, northern North Sea as a type example of such a reservoir. The two most significant elements of the synchronous cementation and migration model are that burial cementation in the reservoir occurs over a restricted time interval, probably less than 10 Ma and that rapid and widespread fluid circulation is not invoked to explain the concentrations of cements observed. We speculate that cementation takes place at, and in a series of zones below, the oil-water contact which descends as oil fills the reservoir, with little change to the bulk chemistry of the reservoir formation waters through time.

Diagenesis and reservoir quality evolution of the paleogene sokor1 sandstones in the agadem block, termit basin, eastern Niger

“…At this stage, coating the detrital quartz grains, quartz overgrowth lead to decrease pore radii and then reducing porosity and permeability of the Sokor1 sandstones. Generally, it is accepted that aqueous pore fluids displacement by hydrocarbons can inhibit the progress of diagenetic reactions thereby stopping precipitation of quartz cement (Kantorowicz 1985, Emery et al 1993, Worden et al 1998, Kraishan et al 2000, Heasley et al 2000, Marchand et al 2002, Molenaar et al 2008. Therefore the overall lack of quartz cement in Sokor1 sandstones during the eodiagenesis stage could be in part attributed to early emplacement of oil.…”

Influence of reservoir oil charging on diagenesis and reservoir quality: An example from Dunlin Reservoir Sandstones, East Shetland Basin, North Sea, UK

“…Besides these controlling factors, recent studies (e.g., Emery et al, 1993;Gluyas et al, 1993;Marchand et al, 2000Marchand et al, , 2002Saigal et al, 1992;Wilkinson et al, 2004;Wilkinson & Haszeldine, 2011;Xia et al, 2020) have highlighted the impact of hydrocarbon charging on reservoir diagenesis and quality. According to these studies, petroleum emplacement in reservoirs can prevent mechanical compaction through over-pressuring; and modifies the wettability of reservoir pores, thereby reducing or inhibiting the rate of reactions between mineral grains and water.…”