Quartz cementation inhibited by crestal oil charge: Miller deep water sandstone, UK North Sea

In the Miller Field, diagenetic quartz abundance, isotopic compositions and salinities of quartz-cementing fluids display a distinct pattern which is related to the structural depth of the reservoir sandstones. Qual iz cement volumes increase from the crest of the field (average 6.0 +/- 1.5%) toward s the flanks of the field (average 13.2 +/- 2.1%) and directly reduce reser voir porosity. By integrating petrographic observations with results of flu id inclusion measurements and O isotope analyses of diagenetic quartz, the pattern of quartz cementation is seen to be related to the reservoir filing history. Oil filled the crest of the reservoir first and prevented extensi ve quartz cementation. At greater depth in the reservoir oil zone, quartz o vergrowths continued to precipitate until inhibited by the developing oil c olumn. Oxygen isotope compositions of diagenetic quartz imply that quartz c ement continued to precipitate in the water zone of the reservoir up to the present day.