الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The present Nile Delta covers an onshore area of about 30,000 km2 and about an equal size offshore down to the 200 m isobath. The delta reaches expands some 240 km along the Mediterranean coastline and extends to a maximum of 160 km from north to south. The Nile Delta represents about 2.4% of total area of Egypt; without the Nile Valley and Delta, Egypt is mainly a desert country. The southern apex of the delta is located approximately 30 km north of Cairo.
The Nile Delta occupies a central position within the plate tectonic development of the eastern Mediterranean. It lies on the northeastern margin of the African plate extending from the subduction zone adjacent to the Cretan and Cyprus arcs to the Red Sea where it rifted from the Arabian plate.
The Nile Delta formed by the subdivision of the River Nile into branches as it flows north through its valley in Upper Egypt. The river branches spread out in a V-shaped fan and make their way towards the Mediterranean through Lower Egypt, where the Nile River splits into the western Rosetta branch and the eastern Damietta branch. In ancient times the Nile flood deposited layers of silt in this area, making the deltaic fan expand from east to west and pushed out into the sea.
The Nile Delta’s geologic history became known due to the activities of the oil companies which started work in the Nile Delta in the early sixties of the last century. This can be attributed to the fact that this province started to disclose part of its hidden hydrocarbon reserves as a direct result of using state of the art exploration techniques, in addition to the expanding the use of different types of geological and geophysical modeling techniques.
The present Nile Delta is known as Neogene-Quaternary Delta. The Fayum Delta (Late Eocene – Oligocene) and Moghra Delta (Early Miocene) are the ancestry of the present Nile Delta. The Fayum Delta and Moghra represent deposits of an ancestral Nile, which flowed in a northwesterly direction across the present – day El Bahr depression into the Mediterranean Sea, after that an eastward shift of the Nile and its delta took place during Early to Middle Miocene time forming the present Nile Delta (Neogene – Quaternary Nile Delta). The shifting of river from west to east may be as a result of tilting and crustal movements that affected northern Egypt.
The study area, Abu Madi gas field, lies in the northeastern part of the Nile Delta, west Dimmetta branch. It extends between Latitudes 31 ̊ 07’ N to 31 ̊ 15’ N and Longitudes 31 ̊ 23’ E to 31 ̊ 28’ E. The geology and the entrapment mechanism of the Nile Delta are still under discussion because the Delta does not have any outcrops of old rocks, where it is covered by the Holocene. The sedimentary rocks represented in Bilqas, Mit-Ghamr, El-Wastani, Kafr El Sheikh, Abu Madi, Qawasim, Sidi Salem and Qantara formations penetrated in Abu Madi Field consist of thick clastics representing Miocene – Holocene time interval.
This study aims to evaluate geologic controls that governed pore pressure of the shale formations in the Abu Madi area. It also evaluates the diagenetic characteristics of some Lower-Middle Pliocene Kafr El Sheikh Formation and other reactive shales in this gas field. According to the values of pore pressure, mud density will be optimized, so that the well will be drilled safely, hence costs and drilling problems can be reduced. Every method used to predict or recognize changes in pore pressure is based on formation compaction. Compaction occurs primarily in shale, so most prediction methods are based on events during drilling or logging shale intervals. In normal cases shale becomes denser with depth.
The shale density and transit time derived from wire line logs were plotted in an attempt to identify deviation from established trends, which indicates changes in pore pressure. The wire line logs were used in qualitative and quantitative manners to predict abnormal pressure zones. The relation between pore pressure anomalies and tectonic setting in the study area was determined. This deviation is interpreted as a result of shale diagenesis, and tectonics; all have positive effect in the budget of the study area.
The NGR is a wire line log which measure the percentage of Gamma Ray, Uranium, Potassium and Thorium in shale formations which helped in determining intervals with clay mineralogical diagenesis with depth from montmorillonite to illite, so that will be a reason for the abnormal pore pressure in that intervals which confirmed by other wire line logs and pore pressure estimation methods.
Base map of the study area and formation tops data were used for the construction isopach and structure contour maps.
Density extrapolation method has been used to calculate the overburden stress (vertical stress), Gamma ray discrimination and V-shale method have been used to differentiate between shale and non-shale zones and Eaton method using sonic log used to calculate pore pressure and fracture gradient, Plumb Bradford correlation method used for calculating the static Young’s modulus, Klimentos permeability method for calculating Biot coefficient, Coats Denoo method for calculating the unconfined compressive strength, Weingarten and Perkins weak sand porosity correlation for calculating the friction angle and Mohr-Coulomb stress model for calculating the maximum and minimum horizontal stresses.
The structure contour map on top Abu Madi Formation shows a NW-SE trending gentle anticline structure, which is delineated by structure contour line of 3025 m (TVDSS) value. This anticline area includes a NW-SE three culminations closed by the structure contour line 3000 m (TVDSS). The highest areas at these culminations have a subsea depth of 2975 m. The well number 10 was drilled in these high structures. However, this structure contour map indicates that, the top of Abu Madi Formation seems to be not affected by faults dissected the area of Abu Madi – El Qar’a Field.
The structure contour map of top Sidi Salem Formation shows that sediments of the formation were deposited on the entire area including the paleo-high region at the middle part where Qawasim Formation is missed. At this pat, Sidi Salem is unconformably overlained by Abu Madi Formation.
Those maps have been built, according to the available formation tops and published maps. Faults layout of the area gives an initial significance to the trends of stresses.
Compilation of the data including drilling, geology and petrophysical data, identification and classification of drilling hazard, identification of the key data, that are missing to build the mechanical earth model and visualization of the drilling mechanics in a geological and petrophysical context (horizon, formation tops and E-logs) have been completed.
In this study, the well sonic data considered the main pillar in the building of the velocity log, as a first step to construct the 1D geomechanical earth model in Abu Madi gas field.
A new relationship extracted between the compression- and shear-slownesses, to be used, when it is needed, as the DSI logs are rarely recorded.
Based on the sonic model, a new set of relationships between the static and dynamic elastic constants, by studying the interval from 3046 m to 3607 m in the well AM S-1 of the study area, have been developed.in the absence of sonic logs at any well location, a synthetic DTSM log could be extracted and validated according, to the new four steps workflow.
The geomechanical model defines the magnitude and orientation of the three principal stresses, the pore pressure, the elastic properties and the rock strength within the Abu Madi gas field. The estimated pore pressure in Abu Madi field was conducted as one-dimensional mechanical earth model (1D MEM), which have been built by using input data from 5 boreholes, as no image log was available. Cutting description, RFT and drilling events were used to build, calibrate and validate the model, as well as the petrophysical data were integrated and prepared for 1D property logs generation. All the estimated pore pressures were plotted against the wireline data, and all values of the estimated pore pressure were plotted to conclude the setting of pore pressure regime in the study area. from the one-dimensional mechanical earth model (ID MEM) in Abu Madi filed, it was clear that the high estimated pore pressure is result from clay diagenesis. Although clay diagenesis is a contributory factor to abnormal pressure, it is thought to be a secondary rather than a principal cause. By adding to the abnormal pressure, the compaction pressure, it can explain the pressure gradients, which rise more steeply than the overburden gradient. Clay diagenesis interpreted as Th/K cross plot, show illite which is originally converted from montmorillonite.
The recorded pressure in the location of AM S-1 well at depth 3141 m is 1.3 g/cm3 equivalent mud weight. On the other hand, the bottom sandstone streak of Abu Madi Formation is varied from 3166 to 3379 m., the porosity decreased down to 25 %, the SW increased to 50%, the elastic rock properties decreased and the Young’s modulus showed a high value equal 5.1 Mpsi, which tells that, this sandstone streak is very strong and could build a filter cake slowly in the drilling phase, and has sanding production low possibility at the production phase.
Shale showed a gradual increase in the pore pressure, which started with 1.11 gm/cm3 and came to a maximum of 1.31 gm/cm3 at the bottom part of the Qawasim Formation, consequently the 9 5/8” casing was properly set at 3066 m at base Kafr El Shiekh Formation while the mud density was 1.29 gm/cm3 and it just balanced the formation pore pressure.
In the Qawasim Formation from 3529 to 3590 m, the formation pore pressure had varied widely from a minimum of 1.03 gm/cm3 to a maximum of 1.32 gm/cm3 at 3539 m.
Pore pressure prediction for the 8.5” section of AM S-1-5well (from depth 3065 to 3605m) shows over-pressured shales with values of 1.23 g/cm3 ,1.36 g/cm3, 1.28 g/cm3 and 1.29 g/cm3 at depths 3177 m, 3258 m 3498 m and 3539 m; respectively. The pore pressure increased due to the clay diagenesis and compaction equilibrium.
Most drilling-related failures are caused by unstable boreholes, whether these are caused by lost circulation, wellbore instability, or stuck pipe. Rock strength has been computed from the empirical equations, using the elastic properties derived from log measurements, giving a continuous log of unconfined compressive strength. A very high mud weight may lead to tensile failure of the wellbore wall (hydraulic fracturing) with attendant mud losses. Alternatively, if the mud weight is too low, compressive failure occurs as the shears formation at the wellbore wall and caves in or spalls creating breakouts. Formation failure can also be affected by the rock fabrics, but specifically in Abu Madi gas field the main cause of wellbore instability the highly stressed shale especially in Kafr El Sheikh Formation which becomes more active in the deviated boreholes.