Porosity Modification During Progressive Burial in Upper Devonian Leduc Reservoirs, Rimbey-Meadowbrook Reef Trend, Alberta

Porosity (and to some extent permeability) modifications during burial diagenesis of the Rimbey-Meadowbrook reef trend are summarized in a regional context, drawing together data from a number of publications and theses. The present depths of this reef trend vary from 1 km to over 4 km and provide a natural laboratory for studying the effects of progressive burial on carbonates. The effect of diagenesis, particularly dolomitization, on porosity modification is assessed by contrasting undolomitized buildups (e.g. Golden Spike, Strachan D3B) with dolomitized equivalents (e.g. Homeglen, Strachan D3A, Ricinus). This information is compared with parts of the deep basin of west-central Alberta between the Obed and Simonette buildups, whose diagenesis appears to be partly fault controlled. Porosity and permeability data when compared regionally and plotted versus depth show that: 1. During shallow ( 2000 - 3000 m), dolostones are significantly more porous and permeable than limestones. Dolostones are more resistant to pressure solution and thus retain their porosity and permeability much better than limestones. 2. At least four dissolution and fracturing phases are identified. The early phases overlapped with replacement dolomitization and resulted in enhanced effective secondary moldic and vuggy porosity. A brecciation phase postdates the replacement dolomites and predates dolomite and anhydrite cements reflecting solution and collapse of these dolomites during intermediate to deep burial.