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

Abstract

In the Khatatba sandstones (Middle Jurassic, Salam oil field, Egypt), detailed fluid inclusion analyses in the quartz over-growths reveal a complex history. The earliest cement zones precipitated from hot, connate freshwater and seawater (Th = 133-162°C; salinity = 0-3.5 wt.% NaCl eq.). A second phase of quartz precipitated from brines of variable salinities (Th = 125-148°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 from consistently high salinity brine (Th = 114-133°C; salinity = 21-24 wt.% NaCl eq.) associated with oil (Th = 79-127°C) during a period of overall cooling.