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العنوان
Integration of Well Log Evaluation and Seismic Attribute Analysis and its Impact on the Reserve Estimation for Some Reservoirs on the North East, Onshore Wells Nile Delta /
المؤلف
El Dahan, Doha Monier Abd El Aziz Mohamed.
هيئة الاعداد
باحث / Doha Monier Abd El Aziz Mohamed El Dahan
مشرف / Abdallah Mahmoud
مشرف / Azza Mahmoud Abd El-Latif El-Rawy
مناقش / Samir Mohamed Raslan
تاريخ النشر
2017.
عدد الصفحات
200p. :
اللغة
الإنجليزية
الدرجة
ماجستير
التخصص
الجيوفيزياء
تاريخ الإجازة
1/1/2017
مكان الإجازة
جامعة عين شمس - كلية العلوم - جيوفزياء
الفهرس
Only 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 in the northeast onshore area of the Nile Delta in West EL Manzala concession. The area includes two gas fields (El Wastani and Dabyaa fields).
The main aim of this study is to integrate the well log evaluation and seismic attribute analysis and its impact on the reserve estimation for some reservoirs in the northeast onshore Nile Delta. This objective has been achieved by evaluating the well logs of Upper and Lower Abu Madi reservoirs and mapping different seismic attributes. These tasks were followed by statistical correlation between the petrophysical results and seismic attributes 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 eight wells in addition to core data for one well. The seismic data consist of 16 seismic lines with check-shot data of some of the wells. Techlog software, Petrel software and OpendTect software have been used in this study.
The seismic data interpretation involved mapping horizons and faults. To start this mapping, six synthetic seismograms were constructed for seismic to well tie. Horizon mapping included mapping four different horizons and the faults. These horizons are Top Upper Abu Madi, Top Gas Sand of Upper Abu Madi, Top Lower Abu Madi, and Top Base Lower Abu Madi. Four horizon maps have been constructed in time domain and were depth-converted to construct four maps in depth domain. The seismic interpretation concludes the presence of two 4-way dip closures dissected by a series of normal faults in the study area. The eastern closure is approximately 5x5 Km in dimensions and has structural relief (structural closure) equal to about 25 msec. (45 m). This closure is dissected by a set of NW-SE oriented normal faults with throws ranging from 12 to 27 msec. The northwestern closure is approximately 2.5x2 Km in dimensions and has structural relief (structural closure) equal to about 15 msec. (15 m). The western flank of this closure is dissected by a set of NNW-SSE oriented normal faults with throws ranging from 11 to 54 msec. This closure lies on the upthrown side of a large fault that has arcuate outline on the top Upper Abu Madi map.
Seismic amplitude extractions focused on the following derived attributes:
 Time-based (isochron) attributes.
 Amplitude-based (RMS amplitude) attributes.
 Waveform-similarity (horizon-based coherence and coherence volume) attributes.
 Frequency-based (spectral decomposition) attributes.
Isochron maps have been constructed for the Lower and Upper Abu Madi by subtracting the base interpolated horizon from the top interpolated horizon of the mapped events. They show the changes in thickness of these two units in the study area.
RMS amplitude maps were created for Upper Abu Madi reservoir package by using the reflectivity volume for the top Abu Madi as well as for the top Gas Sand and 50 msec. below and above it. For the Lower Abu Madi Reservoir package, RMS amplitude maps were created by using different windows, at the top surface of the reservoir package and 50 msec. below and above that surface. These maps clearly show that the sand fairways at the top Gas Sand and top Lower Abu Madi are aligned in NW-SE oriented zones.
A Variance volume was generated using the second-generation coherence algorithm (Petrel 2013) for time window equal to 10 msec. above and 10 msec. below the top Upper Abu Madi grid, and 10 msec above and 10 msec below top Lower Abu Madi grid. It was calculated for the extent of the whole cube (the lateral coverage of the time grid).
The Coherency attributes done on the Top Upper and Top Lower Abu Madi aided in the detection the faults in the study area and the reservoir fairway distribution.
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 interval (Upper and Lower Abu Madi reservoir packages) by using SpecDecomp-tuning cube of OpendTect software. The frequency ranges that were used in tuning cube calculations were set to 0-30 Hz. The software extracts and flats this slab of data then discrete Fourier transform was applied to this slab of data in order to produce the tuning cube.
from the amplitude spectrum window the seismic could be split into different frequency ranges, as Low Frequency range (10 – 25 Hz), Medium Frequency range (30 – 45 Hz) and High Frequency range (50 – 65 Hz). An amplitude map has been created at each frequency at 5 Hz increments. from observations of these maps, the most representative maps for the reservoir fairway definition are at frequencies 15, 30 and 55 Hz. Red Green Blue (RGB) color blended maps were created mixing these three frequencies into the same map. A set of six RGB color blended maps for Upper Abu Madi have been created, and six RGB color blended maps for Lower Abu Madi have also been created. from the RGB maps, a number of well-defined reservoir fairways more or less with a consistent northwest trend have been observed. This follows the known regional depositional dip in the area. In general, the reservoir fairways are narrow (300 – 700 m wide).
Formation evaluation of the Upper and Lower Abu Madi units in eight wells in the study area led to the following conclusions:
1- The net thickness of sandstone in the Upper Abu Madi increases towards the south whereas in the Lower Abu Madi unit it increases towards the west in Pay 1 and towards the northwest in Pay 2.
2- The shale content in the Upper Abu Madi pay zone shows high shale percentage at the southwestern part of the study area at well EW-13 and minimum shale content at the northern part of the study area at EW-8 well. The shale content in the Lower Abu Madi pay zones shows that for Pay 1 there is high shale percentage at the southeastern part of the study area at well EWE-2 and minimum shale content at the southwestern and northeastern parts of the area at EW-13 and Dabayaa-2 wells, respectively. The shale content in the Lower Abu Madi Pay 2 shows that the shale content increases in the southeast to more than 20% at well EW-13 and decreases in the northwest to less than 15% at wells EW-6 and EWW-2.
3- The lateral variation in effective porosity values in Upper Abu Madi is from lowest value at EW-13 and highest value at the northwestern part of the area at EW-8. The effective porosity distribution map for the pay 1 in Lower Abu Madi unit reveals that the lowest porosity values are at EWW-2 and EWE-2 wells in the southeastern and northwestern parts of the study area. The effective porosity map of pay 2 in the Lower Abu Madi unit indicates that the porosity reaches its highest values of 20.5% in the northwestern part of the area at well EWW-2.
4- The hydrocarbon saturation in the Upper Abu Madi pay shows the highest hydrocarbon saturation towards the southeastern part of the study area at EWE-2 well and the lowest hydrocarbon saturation towards the north at EW-8 well (32-48%). The hydrocarbon saturation of pay 1 in the Lower Abu Madi reservoir decreases towards the northwestern part of the study area (35-67%). The hydrocarbon saturation of pay 2 in the Lower Abu Madi reservoir decreases toward the southern part of the area where it reaches 37-45%.
5- Definition of the areas of high hydrocarbon saturation, relatively low shale content, high effective porosity, good pay thickness and shallow depth allowed the identification of the promising sites of future hydrocarbon exploration in the study area. For the Upper Abu Madi unit such area is towards the south. For the Lower Abu Madi pay1 such areas are towards the northeastern and western parts of the study area whereas for the Lower Abu Madi pay2 it is towards the northwestern part of the study area.
Petrophysical evaluation of the wells in the study area shows the presence of hydrocarbons within the Messinian Abu Madi 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:
5. There is good negative correlation between VSH and RMS amplitude, where areas of low VSH content correspond to areas of high amplitude anomalies.
6. There is fair correlation between net sand thickness and RMS amplitude.
7. There is fair correlation between HC saturation and RMS amplitude.
8. It is difficult to establish a correlation between seismic amplitudes and porosity. This may be because porosity is affected by a number of factors like shaliness of the rock, compaction and cementation.
from the volumetric calculations, it is clear that the eastern closure at the Lower Abu Madi level holds the highest volumes of hydrocarbons (97 bcf mean inplace gas), while the western closure of the Lower Abu Madi and the eastern closure of the Upper Abu Madi hold less volumes (51 bcf and 2.9 bcf inplace gas respectively).