Bio- and Sequence Stratigraphy of the Pliocene Rocks in Temsah Gas Field , offshore Nile Delta , Egypt

Abstract

The sequence stratigraphy is an essential explorationist tool for local hydrocarbon exploration, reservoir evaluaton and also regional studies. The present study based on the integration between 3D modelling of the structural elements that affect the basin and the effect of tectonical stresses on the depositional current direction, biostratratigraphic investigation processed from ditch cutting samples collected from three boreholes penetrated Rosetta, Kafr El- Sheikh and Wastani Formations, wireline well log interpretation and petrophysical analysis estimated for six wells distributed around the study area , seismic stratigraphic interpretation of seismic well section constructed for an area of 65 km2 and finally property modelling for each prospective sand reservoir distributed in the area, allowed to understanding and achieve the aim of the present study that discussed before. Subsurface geologic interpretation of the structural pattern observed that the area is affected by three normal, growth and gravitational main bounded faults trended NE-SW direction that subdivided the area into three main sectors and many small scale synthetic and antithetic faults resulted in the formation of tilted rotational fault blocks dipped in the NW direction and deformed- undeformed rollover anticlines act as structural seal for hydrocarbon potentiality. This structural pattern affected the depositional current direction and resulted in the formation of syn-depositional delta slope channels in the study area. Biostratigraphic consideration of the study area depending on 109 ditch cutting sample prepared for foraminiferal and nannofossil investigation allowed to establish bio-chronostratigraphic subdivision of Kafr El-Sheikh formation into standard chrono-biostratigraphic zones then standard sequence stratigraphic cycles and clarify the paleo-environmental condition for each sequence. 4 . Summary and Conclusion 173 standard planktonic foraminiferal biozones have been identified in the Pliocene sucession depend on quantitative analysis. These planktonic zones are arranged from top to bottom as follows: Globorotalia crassaformis (in partim), Globorotalia puncticulata, eq. Globorotalia puncticulata/Globorotalia margaritae, eq. Globorotalia margaritae Zones. Equivalent benthic zones have also been recorded along the same successions. These include: Articulina tubulosa, Bulimina elegans marginata plexus, Bulimina marginata, Anomalinoides helicinus, Cibicides italicus/ Uvigerina rutila Zones. The nannofossil species allowed the subdivision of the studied Pliocene succession into 7 standard biozones, from top to bottom, are as follows: Pseudoemiliana lacunose (NN19), Discoaster brouweri (NN18), Discoaster surculus (NN16), Reticulofenestra pseudoumbilicus (NN15), Discoaster asymmetricus (NN14), Ceratolithus rugosus (NN13) and Amaurolithus tricorniculatus (NN12) Zones. This results enables to construct a bio- and chronostratigraphic correlation of the Early-Late Pliocene Kafr EL-Sheikh Formation and delineate the occurrence of pronounced hiatuses along the Pliocene rocks in the study area. Depending on the foraminiferal facies and the high subdivision of the benthic species, Kafr El-Sheikh formation ranged in the paleoenvironmental conditions from outer neritic-upper epibathyal environment in the lower member to transitional-littoral environment in the upper member due to the regression of the sea level in Late Pliocene and Early Pleistocene age. Consequently, the biostratigraphic data analysis, sequence stratigraphic cycles have been tided on the wireline logs and petrophysical data to estimate the lithologic characters of each cycle identified by the biostratigraphic analysis, sand distribution of each reservoir that represented by the LST of each cycle, true thicknesses of each cycle, depositional current directions and depositional environment of each system tract. The different system tracts (HST, TST