الفهرس 
CHAPTER TWO SEISMIC INTERPRETATIONOnly 14 pages are availabe for public view
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Abstract
Jade field in Matruh basin is one among the most significant fields in the northern part of the Egyptian Western Desert. It attracts the attention of geologists and geophysicists for oil and gas investigation and exploration. This is due to the presence of huge subsurface sedimentary section which include considerable reservoir rocks within the members of the Early Cretaceous Alam EL-Bueib Formation. However, potential source rocks have been encountered within the Jurassic formations and Alam EL-Bueib Formation.
The study area is located in the northern part of the Western Desert, and lies between latitudes 30° 54` 45`` – 30° 57` 45`` N and longitudes 27° 05` 00`` – 27° 09` 45`` E.
The present study deals with evaluation the structural framework, stratigraphy and reservoir characteristics. This is to evaluate the petroleum system and hydrocarbon potentialities of AEB-4, AEB-5 and AEB-6 in the study area using existing 2D seismic reflection data and well data to establish the various reservoir properties that characterize the pay zone.
Lithostratigraphically, the Jade field in Matruh basin comprises rock units ranging from Middle Jurassic to Miocene. The target formation in the study area is Alam EL-Bueib, especially 4, 5 and 6 layers. The Early Cretaceous Alam EL-Bueib Formation is composed mainly of sandstone interbedded with shales, siltstone and carbonate streaks.
Tectonically, the north Western Desert is considered as a part of the unstable shelf of Egypt and therefore its tectonic setting could be determined from surface and subsurface structures. Meshref (1982) considered that northern Egypt seems to be affected by three tectonic events of which the oldest one is most probably of Paleozoic to Triassic age. It was resulted in NW or WNW trending structures. The second event that was resulted in ENE Syrian Arc trending structures of Cretaceous age. The third one is of Late Eocene to Early Oligocene age and was resulted in the NW (Gulf of Suez) and NNE (Aqaba) trending structures. This may be due to the collision of Africa with Asia plates.
Structurally, the NE - SW trend which was especially active during the Late Cretaceous-Early Tertiary time (Syrian Arc System) is traceable on surface structures as in Abu-Roash, Wadi El-Rayan, and Bahariya Oases. The NW - SE trend was reported in several Tertiary surface structures lying to the NE of Siwa and extending between Moghra, Wadi El-Natrun, and the Nile Delta. Faulting is evidenced in the Lower Cretaceous rocks of the northern Western Desert where the strike of these faults is parallel to the Syrian Arc System.
On the other hand, the structural analysis of the available 2D seismic lines data is directed to determine the subsurface entrapping styles within the study area.
Seismic Interpretation, The interpretation of Twenty (20) seismic lines covering the study area led to identify the most important seismic reflectors throughout Alam EL-Bueib Formation especially in 4, 5 and 6 zones. The Alam EL-Bueib 3D structure model – 4, 5, and 6 depict a complicated structural pattern and illustrate the following conclusions:
- NNE-SSW fault (F1) is inverted normal fault can be clearly observed on the seismic sections and consider the master fault in the study area created in Jurassic due to Early Jurassic plate movement and inverted in Late Cretaceous due to strike slip movement which is caused by compressional force of Syrian
- NNW-SSE normal Faults (F2, F3, F4 and F5) are extending from northwest to southeast (NW–SE) direction created due to transtensional deformation of dextral (right lateral) strike slip movement in Late Cretaceous. All the interpreted normal faults (Fault – 2, 3, 4 and F5) on the seismic sections generally form half graben that extends throughout the downthrown side of the master fault in the studied area.
The structural characterization of the Alam EL-Bueib Formation is one of the most essential goals. The Alam EL-Bueib – 4, 5, and 6 zones have been modelled to change the fault structure of the trap. To connect seismic data (time) with well data, a synthetic seismogram was created (depth). The structural architecture of the Alam EL-Bueib reservoirs is depicted using seismic profiles from the Jade field.
Petrophysical characteristics deduced from the process of welllog analysis by using Interactive petrophysics software are generally varied vertically in the form of a litho-saturation cross plot and laterally in the form of iso-parametric maps. The Alam EL–Bueib Formation density-neutron cross-plots reveal the existence of sandstone with some calcareous cement. The distinct petrophysical properties of the Alam El-Buieb-4, Alam El-Buieb-5, and Alam El-Buieb-6 Formation were studied using reservoir physics and well logging data from four wells in the jade oil field. The following conclusions may be drawn from the well log analysis:
• Alam El-Buieb-4 Formation:
- It’s mostly made up of shale, siltstone, and fine sandstone, with some dolomite layers thrown in for good measure. This unit is approximately 620 feet thick.
- The average values of effective porosity in level AEB-4 range from 12% to 14%.
• Alam El-Buieb-5 Formation:
- Is represented mainly by interbedded sand and siltstone with traces of shale. The thickness of this unit is around 280 ft.
- The average values of effective porosity in level AEB-4 range from 12% to 14%.
• Alam El-Buieb-6 Formation:
- Is characterised by the dominance of sandstone as a significant lithological ingredient, with limestone and shale strata. This unit is approximately 950 feet thick.
- The average values of effective porosity in level AEB-4 range from 14% to 16%.
Geochemical examinations within the investigated rock units help in the identification of potential source intervals. The organic richness of Jurassic source rocks ranges from fair to excellent. The organic richness of the Lower Cretaceous Alam EL-Bueib source rocks is considered fair to good, with kerogen type (III), indicating its capacity to yield mostly gas with minimal oil. The source rocks Alam EL-Bueib – 4 and 6 are at the mature stage of oil production. Kerogen type (III) is found in Jurassic source rocks, with input of type (II), indicating that the majority of Jurassic source rocks may generate gas with little oil. Within the oil and gas generation stage, the Jurassic source rocks, particularly the Upper and Lower Safa source rocks, are at a late to over mature stage.
The petroleum system of the study area includes elements and processes. The elements consist of the source rock, reservoir rock, seal rock and trap, while the processes include generation, maturation, migration and accumulation, and also the preservation of the hydrocarbons once in the trap.
Petroleum system elements
A- The source rocks were evaluated by calculating the organic carbon content (TOC wt.%). These TOC values were determined within the Lower Cretaceous Alam EL-Bueib and the Jurassic source rocks. The TOC values of the Alam EL-Bueib source rocks range from 0.59 to 2.09 wt.% with average value of 1.26 wt.%. The source rocks of Alam EL-Bueib Formation are considered as fair to good source rock except Alam EL-Bueib – 4 consider very good,, while the TOC values of the Jurassic source rocks range from 0.19 to 40.7 wt.% with average value of 6.1 wt.%. The Jurassic source rocks show good to very good organic richness in most zones, especially in Upper and Lower Safa.
B- The shale volume, effective porosity, water saturation, hydrocarbon saturation, reservoir and net pay thicknesses are all represented by iso-parametric maps in the reservoir rocks characterisation. The following was the interpretation of these maps::
1- The shale volume ranges from 8.1 to 16.6%, 4 to 6.3% and 3.4 to 9.6 % for Alam EL-Bueib – 4, 5 and 6 reservoirs respectively.
2- The effective porosities of the investigated area indicate that the effective porosity of the Alam EL-Bueib – 6 reservoir ranges from 12 to 16%, while the effective porosity of the Alam EL-Bueib – 4 and 5 reservoirs ranges from 12.5 to 14.8 % .
3- The water and hydrocarbon saturations distribution maps reveal that the variation of the water saturation of the Alam EL-Bueib – 4 reservoir ranges from 25.8 to 64.8%, while the hydrocarbon saturation shows traditionally a reverse pattern to that of the water saturation. It varies between 35.2 and 74.2%. The water saturation of the Alam EL-Bueib – 5 reservoir ranges from 40 to 50 %, while the hydrocarbon saturation varies from 50 to 60 %. The water saturation of the Alam EL-Bueib – 6 reservoir ranges from 30 to 70%. By contrast the hydrocarbon saturation of the Alam EL-Bueib – 6 reservoir ranges from 30 to 70%.
C- Seal rocks indicates that the Alam EL-Bueib reservoirs are sealed by local intra-formational shale intervals of Alam EL-Bueib - 3F, 3D and 3C members and effective compact carbonates of Alam EL-Bueib – 2 Member and Alamein Formation.
D- Traps, inspection of the 2D seismic lines of the study area, trap is typically of the structural type, consisting mainly of faulted anticlinal features. Trap is developed in NE-SW oriented faulted blocks. The master fault (Fault - 1) in the study area created in Jurassic due to Early Jurassic plate movement and inverted in Late Cretaceous due to Syrian Arc system movement. The master fault is extending from northeast to southwest (NE–SW) direction.
Transformation cycle
1. The maturity of a source rocks reflect the ambient pressure and temperature. According the basin analysis, the rocks which have vitrinite reflectance (%Ro) between 0.8 and 1.35% are described as mature source rocks, while the rocks which contain vitrinite reflectance (%Ro) values greater than 1.35% is described as over mature rocks. On the other hand, the rocks which have vitrinite reflectance (%Ro) values less than 0.8% is described as immature. In the study area, the vitrinite reflectance (%Ro) is between 0.74 to 0.79% for Alam EL-Bueib source rocks and between 0.93 and 1.4% for Jurassic source rocks.
2. Burial and thermal history models of the studied wells were constructed using PetroMod 2012.2 software. The data needed to construct these models include (Formation tops or true stratigraphic thickness, Geologic age of the time-rock unit, geothermal gradient, erosion and the non-deposition periods or hiatus. Accordingly, four burial histories and hydrocarbon generation models were constructed for (jade -1X, Jade-2X, Jade-6 and Jade-5), these burial history curves are plotted from the geological data of the studied wells. The timing of hydrocarbon generation and expulsion of the source rock is assessed by reconstruction of 1D model of burial history of the studied wells.
The most hydrocarbons were generated at temperatures between 66 and 177 °C (" ~ "150 – 350 °F), corresponding to burial depths of 1220 to 6100 m (" ~ " 4000 – 20000 ft). The oil window for each well is indication of the hydrocarbon generation potentiality of the source rock in the study area. The depth of oil window is varying from well to another. The depths of oil window in the study area range from 8074 to 11282 ft and the depth of onset gas generation around 13501 ft. All these values are accepted with the standard depths suggested to generated oil and gas.
3. Migration occurred vertically from the underlying Jurassic source rocks along the fault plane to be accumulated in the Lower Cretaceous Alam EL-Bueib reservoirs and may be related to the depocenter of the Alam EL-Bueib Formation sources.
Generally, the integrating of the petrophysical evaluation together with the structural investigations of the study area, it can be stated that the Alam El-Bueib Formation contains good reservoirs. Also, the Alam EL-Bueib Member (Alam EL-Bueib – 4, 5 and 6) have good porosity which make them be favorable for oil and gas accumulation especially, toward the central southern and northern parts of the study supported by high structure of these parts.