Pore fluid evolution and quartz diagenesis in the Khatatba Formation, Western Desert, Egypt

In the Khatatba sandstones (Middle Jurassic, Salam oil field, Egypt), detai led fluid inclusion analyses in the quartz overgrowths reveal a complex his tory. The earliest cement zones precipitated from hot, connate freshwater a nd seawater (Th = 133-162 degrees C; salinity = 0-3.5 wt.% NaCl eq.). A sec ond phase of quartz precipitated from brines of variable salinities (Th = 1 25-148 degrees C; salinity = 5-20-wt.% NaCl eq.), inconsistent with connate fluids. Both phases of quartz cementation resulted from multiple events of injection of hot fluids related to fracturing, quartz precipitation being caused by cooling after injection. The final phase of quartz precipitated f rom consistently high salinity brine (Th = 114-133 degrees C; salinity = 21 -24 wt.% NaCl eq.) associated with oil (Th = 79-127 degrees C) during a per iod of overall cooling. (C) 2000 Elsevier Science B.V. All rights reserved.