Salt is one of the most effective agents for trapping oil and gas. As a ductile material, it can move and deform surrounding sediments and create traps. However, effective sealing of reservoirs for movement of hydrocarbons along breaching faults or fracture swarms (i.e., macroseepage) is a different mechanism than the movement of hydrocarbons on a molecular scale along grain boundaries and microfractures as happens with microseepage. To address salt seal integrity, Forum Exploration has chosen to evaluate the applicability of passive surface geochemical surveys for mapping hydrocarbons in their onshore West Gebel El Zeit lease in part due to difficulties in seismic imaging through salt and anhydrite sequences. Two economic producing wells have been drilled in the lease, but due to compartmentalization and complexity in the area, three dry wells also have been drilled. Target formations include the Kareem Formation at approximately 2700 m and the Rudeis Formation at approximately 3000 m. The geochemical survey encompasses 100 passive geochemical modules. Passive samplers also have been deployed around two producing wells and one dry well for geochemical calibration. Calibration data indicate positive thermogenic signatures around the two producing wells in contrast to the background or baseline signature from around the dry well. The Kareem Formation calibration signature ranges from approximately C6 to C12 with the Rudeis Formation calibration signature ranging from C5 to C9. This suggests that the Rudeis calibration signature is lighter than the Kareem, in agreement with independent measurement of American Petroleum Institute (API) gravity on produced oil samples (API gravity 41° oil for the Rudeis and 35° oil for the Kareem). A postsurvey well, Fh85-8, has been drilled based on combined geochemical and seismic data results. The well is a Kareem oil discovery, with an initial production of approximately 800 barrels of oil per day. We have developed evidence in this Gulf of Suez example to show that microseepage occurs through substantial salt sequences. Consequently, ultrasensitive passive surface geochemical surveys provide a powerful tool for derisking salt plays.

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