The Middle Cambrian Deimena Group sandstones are the main oil reservoir in Lithuania with 18 oilfields discovered so far in the western part of Lithuania. The sandstones show a great variability in reservoir quality, making the reservoir exploration and the construction of its models difficult. The porosity and permeability show a complicated variability even within a single oilfield; closely spaced wells within a single oilfield may have a different reservoir quality, whereas in the vertical sense their properties also vary greatly within the reservoir bodies. Quartz cementation is the main diagenetic process influencing and controlling the petrophysical properties of Cambrian sandstones. The amount of quartz cement, and inversely its porosity and permeability, are only weakly correlated with the burial depth and palaeotemperature within particular oilfields. Evidently, factors other than general physical conditions and overall chemical conditions related to burial depth must locally have influenced the processes involved in quartz cementation and controlled the location and amounts of quartz cement. The main factor is the reservoir architecture. The amount of quartz cement positively correlates with the amount of shale structures in sandstone bodies. Clay-induced chemical compaction and pressure solution of detrital quartz at shale–sandstone contacts and within thin shale lamina is the main process yielding silica for local quartz cement. The supply of silica for quartz cement in the sandstones is thus dependent on the number of thin clay lamina and clay intercalations within the reservoir sandstones. The sandstone/shale ratio and the thickness of sandstone bodies control the location and degree of quartz cementation and thus the reservoir quality.

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2011 - Vol.53
No. 1, No. 2, No. 3

2010 - Vol.52
No. 1-4

2009 - Vol.51
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2008 - Vol.50
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2007
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2006
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2005
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2004
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2003
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2002
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2001
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