الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The Nile Delta basin is the most prolific, prospective gas and condensate province in Egypt. The Nile Delta is the main gas producing province in the northern part of Egypt with approximately 62 TCF proven reserve. 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 soils. The area of study is located 120-150 km from Alexandria, deep water (250-1500m) North west margin of Nile delta cone.
The main aim of this study is to integrate the well log evaluation , seismic attribute analysis and modelling to show its impact on the reserve estimation for some reservoirs in the western offshore Nile Delta. This objective has been achieved by evaluating the well logs of El-Wastani reservoirs and mapping different seismic attributes. These tasks were followed by statistical correlation between the petrophysical results , seismic attributes and modelling to evaluate the impact of the well logs and seismic on the reserve estimations.
The present study made use of a data set consisting of borehole and seismic data. Borehole data include a full set of well logs for Five wells in addition to core data for one well. The seismic data in depth domain provided with composite logs for the wells. Techlog software, Petrel software and OpendTect software have been used in this study.
The seismic data interpretation involved mapping horizons. To start this mapping, Horizon mapping included mapping nine different horizons. These horizons are top and base of each four channels.
The seismic interpretation concludes the presence of two 4-way dip closures.
Applying different workflows on the seismic data enabled understanding the distribution and delineation of channel fairways, Among the workflows tested seismic attribute extractions from different cubes as RMS, Coherency, Sweetness and Envelope are conducted, on window extractions between the top and base of each channel.
Isochore maps have been constructed for the four channels by subtracting the base interpolated horizon from the top interpolated horizon of each channel. They show the changes in thickness of these four units in the study area.
RMS amplitude maps were created for Saffron reservoir package by using the reflectivity volume between top and base of each Channel. These maps clearly show that the sand fairways of El-Wastani channels are aligned in NNW-SSE oriented zones.
A Coherence volume was generated using the second-generation coherence algorithm (Petrel 2017) for Depth window between top and base of each channel using horizon probe. It was calculated for the extent of the whole cube (the lateral coverage of the depth grid).
Sweetness and Envelope cubes were generated for depth window between top and base of each channel using horizon probe. It was calculated to help oin delineation of the maximum channel polygon.
SD frequency analysis was conducted and showed detail on thinner bed not captured by the seismic attribute extractions nor geobody extraction workflows.
Spectral decomposition (SD) is a technique that breaks down seismic signal into narrow frequency sub-bands. When these sub-bands are examined in a spatial context (i.e., plan view of a 3-D survey) they reveal interference that is occurring across the available bandwidth of signal so that it makes use of much lower seismic frequencies to image the reflective nature of the subsurface rock mass. Such decomposition provides greater resolution and detection of the layer stacking heterogeneity, boundaries, and thickness variability than are possible with traditional broadband seismic attributes. A tuning cube has been created for each channel (between top and base) by using Spec. Decomp-tuning cube of OpendTect software. from the amplitude spectrum window. The seismic could be split into different frequency ranges, as Low Frequency range (0 – 10 Hz), Medium Frequency range (15 – 25 Hz) and High Frequency range (30 – 69Hz). An amplitude map has been created at frequency at 3,9,21,36,54,69 Hz (Figures 4.27 to 4.32). from observations of these maps, the most representative maps for the reservoir fairway definition are at frequencies 9, 21 and 36 Hz.
Red Green Blue (RGB) color blended maps were created mixing these three frequencies into the same map. A set of ten RGB color blended maps for El-Wastani channels have been created and shown on Channel 1 by applying different window sand four RGB color blended maps for El-Wastani channels (Top-Base) have been chosen that clarify the channel fairways. from the RGB maps, we can observe a number of well-defined reservoir fairways more or less with a consistent NNW-SSE trend.
Geo-body extraction attribute was creating by blending different seismic cubes (RMS, RGB SD, Sweetness and Envelope) then adjustment opacity threshold value and amplitude window. Geo-body extraction attribute delineates stratigraphic features, lateral and vertical extension of the channels.
Petrophysical evaluation of the wells in the study area shows the presence of hydrocarbons within the Pleistocene/Pliocene El-Wastani sands with good reservoir parameters. Analysis of the Modular Dynamic Tester data confirms the presence of hydrocarbons. Observations on the seismic amplitude extractions and the petrophysical evaluation results led to the following conclusions:
1. There is good negative correlation between VSH and RMS amplitude, where areas of low VSH content correspond to areas of high amplitude anomalies.
2. There is good correlation between net sand thickness, gas saturation, porosity and RMS amplitude.
3. Use of seismic sections, attribute analysis and geobody extractions help in robust delineation of channels.
4. Geobody from Envelope, RMS amplitude extraction maps, RGB horizon probes showed the best channel details of channels 1, 2 and
5. Envelope and sweetness horizon probes showed details of channel 4 (different fluid fill)
6. GIIP calculated from static reservoir model is closest to the GIIP result from the field production data
Static reservoir characterization created to provid the initial distribution of properties over the prospect needed for reservoir modelling.
The parameters of Saffron Field channel reservoirs; Channel 1, Channel 2, Channel 3 and Channel 4 are calculated to estimate the three different types of models:
1. Structural modelling to identify different structure pattern in the area.
2. Facies modelling which characterize different facies/depositional elements composing Late Pliocene Saffron Field channel’s reservoirs.
3. Petrophysical modelling for detection petrophysical distribution within channel reservoirs.
The final step is volumetrics that can be calculated by several methods according to the input parameters in either a probabilistic or stochastic approach. Understanding how each method and their inputs affect the resulting volumetrics is key to determine which method yields a sensible calculation.
Six volumetrics calculation methods have been conducted on the hydrocarbon bearing reservoirs of the Saffron channels. These methods included geobodies extracted from RMS, Sweetness, Envelope, and RGB SDs cubes, reservoir modelling as well as area vs. depth method all populated with the petrophysical averages calculated from the area wells.
It was found that the volumetrics method (volumetrics case) which uses reservoir modelling yields a volume closest to the actual field volumes proven after several years of production. It is recommended to perform this workflow in other areas to confidently calculate the hydrocarbon volumetrics within the reservoir features.