INFLUENCE OF DIAGENESIS AND DEPOSITIONAL
CONDITIONS ON LOWERING SANDSTONE RESERVOIR QUALITY OF ABU ROASH "E" MEMBER, ABU SENNAN
AREA, NORTH WESTERN DESERT, EGYPT
MOUNIR K. SAAD
Dept. Geology, Fac, Sciences, Cairo Univ., Giza, Egypt
|
The sediments of Abu Roash "E" Member (Turonian), Abu Sennan field, are sandstones commonly intercalated with shales and limestones. Their depositional mechanism is interpreted from core descriptions, sedimentary structures and wireline log data. Where core data are lacking, electric imagery logs and ditch cutting samples have proven useful in making lithic assessments. Based on the gamma ray responses and rock types. the Abu Roash "E" Mbr is subdivided into upper (transitional sand and mud intertidal flats) and lower (shallow marine) units. Small scale planner cross laminations, low amplitude ripple laminations, flaser, wavy and lenticular bedding, horizontal rhythmic laminations and bioturbation are the main primary sedimentary structures recorded in the sandstones of the intertidal flat unit. Fluctuations of cementation, porosity and permeability were controlled directly or indirectly by conditions during and soon after deposition.
The damaging problem of the sandstone reservoir is bifolded. The introduction of massive amounts of detrital clays in a laminated and bioturbated manner drastically destroys porosity and pore interconnectivity. On the other hand, the relatively clean sandstone (clay matrix free) shows severe sealing of pore spaces by the poikilotopic ferroan calcite cement, quartz over-growths and authigenic clays. The dual interplay of depositional conditions and diagenetic pathways significantly lower the reservoir quality.
|
|