--> ABSTRACT: Quantifying the Inhibiting Effect of Oil Charge on Quartz Cementation in Clastic Reservoirs, by Ann M. E. Marchand, Stuart S. Haszeldine, Anthony E. Fallick, and Craig Smalley; #90906(2001)

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Ann M.E. Marchand1, Stuart S Haszeldine1, Anthony E Fallick2, Craig Smalley3

(1) University of Edinburgh, Edinburgh, Scotland
(2) SUERC, Scotland
(3) BP Amoco, Sunbury-on-Thames, England

ABSTRACT: Quantifying the Inhibiting Effect of Oil Charge on Quartz Cementation in Clastic Reservoirs

Controversy exists as to the extent that oil charge inhibits quartz cementation in clastic reservoirs. The Brae Formation reservoirs in the Miller and Kingfisher Fields (North Sea) provide good empirical evidence of the inhibiting effect of oil on quartz cementation : low quartz cement volumes and high porosities are preserved in structural highs or early charged reservoirs; high quartz cement volumes and lower porosities occur in aquifers and recently charged reservoirs. The effect of oil on quartz cementation was quantified by combining petrographic results with fluid inclusion data, basin modelling and kinetic modelling of quartz cementation.

Fluid inclusion data indicate that quartz cementation commenced around 70ºC. Maximum temperatures from fluid inclusions in the crest of the reservoir in the Miller Field are ~95ºC and increase towards the OWC (~118ºC). In the Kingfisher Field, maximum temperatures in fluid inclusions are overall ~100ºC. In both these reservoirs, present day temperature is 120ºC. Basin modelling results confirm that oil emplacement inhibited quartz cementation in oil zones : oil emplacement occurred from 40 to 10Ma in Miller (~90 to 120ºC) and around 30 to 20Ma in Kingfisher (~95-105ºC). Quartz cementation rates in oil and water zones were calculated by numerical modelling. Results show that oil zone cementation rates (~10-21moles/cm2.s) are at least two orders of magnitude lower than water zone cementation rates (~10-19moles/cm2.s).

Overestimation of quartz cement volumes in reservoirs (and underestimation of porosity) occurs if the effect of oil on quartz cementation is not taken into account, resulting in erroneous reservoir performance assessments.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado