ABSTRACT

Surface prospecting for hydrocarbons has been carried out on the gypsum deposits at W.Gasus, W. Syatine, Hamrawein and W.Wizr along the Red Sea coast.
Fluid inclusions study recognized the presence of aqueous and hydrocarbon – bearing inclusions. These inclusions are coexisting, and distributed mainly along microfractures of gypsum crystals as secondary inclusions. Primary hydrocarbon bearing inclusions are rare and observed only in Hamrawein gypsum deposits, and are associated with aqueous, and CO2 -bearing inclusions.
Microthermometric results of secondary aqueous inclusions indicate that the salt system was composed mainly of Ca ±Mg (as indicated from eutectic temperature). Salinity is low and ranging between 3.39 and 7.17 wt. % NaCl eq. Total homogenization was achieved at temperatures between 75 and 130 C. On the other hand primary aqueous inclusions are higher in salinity (8.86 to13.7 wt. % NaCl eq.), and lower in total homogenization temperature (50 to 70 C) relative to secondary inclusions.
Secondary hydrocarbon-bearing inclusions homogenized at temperatures lower than
-82.1 C (between -82.5 and -96 C), while the primary inclusions homogenized at temperatures higher than -82.1 C, between -68 and -75 C. Total homogenization was achieved at temperatures between 85 and 126 C in the secondary inclusions and was never achieved in the primary inclusions.
In primary CO2– bearing inclusions, the homogenization temperature of CO2 was observed to liquid at temperatures between 25.6 and 30.5 C.
IR spectrophotometer investigation lead to the determination of aliphatic chains of C-H, cyano group (C≡N), carbonyl group (-C=O), ethylenic group (C=C) and OH., in addition to heterocompounds of N, S, and O. Chemical analyses of gypsum shows relatively high content of TOC with average ranging from 0.19 to 0.68 wt.%. This in addition to the presence of hydrocarbon fluid inclusions along microfractures as secondary inclusions can prove the presence of microseeps of hydrocarbon from the underlain carbonate rocks