A Study of Microfacies and Petrophysical Analysis of Some Subsurface Cretaceous Rocks of Abu Gharadig-34 Well,Western Desert,Egypt

Abstract

The main aim of this study is to shed light on the microfacies association, petrophysical parameters, and depositional environment of different rocks such as sandstone, limestone, shale, siltstone, and dolomite of subsurface Cretaceous rock units (Abu Roash “C” member, Abu Roash “E” Member, and Bahariya Formation) from Abu Gharadig-34 well in the north western desert, Egypt. In this study, nine microfacies were identified. These microfacies include calcareous siltstone, bioclastic wackstone, ferruginous sublithic arenite, dolomitic lithic arenite, lithic arenite, fossiliferous bioclastic wackstone, glauconitic dolomitic sublithic arenite, ferroan dolomite, and ferruginous sandy siltstone. Generally, subsurface Cretaceous rock units are deposited in different depositional environments ranging from tidal flats to open circulation passes through restricted circulation shelves. Statistical analysis of the petrophysical data showed that the highest porosity was concentrated at Abu Roash “C” member, which had very good porosity and high permeability. The porosity increased when the bulk density decreased. The permeability of the studied samples was the same as the porosity, which increased when the bulk density decreased. It can be concluded that Abu Roash “C” member is a good reservoir in the Abu Gharadig-34 well.     

The Petrography,Mineralogy, and Hydrocarbon Potential of the Shales of the Duwi Formation,Abu Tartur,South Western Desert,Egypt

Abstract

Eight shale samples related to the Duwi Formation (Campanian-Maastrichtian) of the Abu Tartur mines of the southwestern desert of Egypt were petrographically, mineralogically, and geochemically studied. The study results indicate that the detrital material of these shales were derived mainly from mafic to ultramafic components of the basement rocks under intensive chemical weathering and deposited in an alkaline reducing marine environment of low energy and these shales do not attain the requirements of hydrocarbon production.     

沉积相对岩石物理特性从岩心到录井尺度粗化的控制及在石油勘探中的意义

有效的粗化岩石物理特性及跨尺度对比对油藏描述及模拟有极重要的意义。本文用统计数学方法探讨沉积过程和沉积相对油藏岩石物理特性跨尺度对比的影响。对单一沉积过程及渐变水动力所产生的油藏(例如滨岸相)岩心与录井的岩石物理特性可以在较大范围内交叉对比。录井的岩石物理特性能比较实际的反映岩心的特性。对多个沉积过程及突变型水动力所产生的油藏(例如三角洲相)岩心与录井的岩石物理特性交叉对比性差。而且录井的岩石物理特性不能实际的反映岩心的特性尤其是对薄层(<1m)泥沙岩交互相油藏。     

Petrophysical evaluation of clastic Upper Safa Member using well logging and core data in the Obaiyed field in the Western Desert of Egypt

Upper Safa Member is part of Jurassic Khatatba Formation; it consists of low net gross ratio sand streaks. The core and well logging data were used to perform a comprehensive reservoir evaluation. The Schlumberger application “Techlog” was used to perform the required evaluation analysis. Four oriented wells were selected for this study. The volume of shale “Vsh” using gamma-ray (GR) was used to evaluate the lithology and to discriminate sand “reservoir” from shale “non-reservoir”. A porosity model using the density log was constructed and used as an input to calculate Archie’s water saturation “Sw”. Porosity- Permeability (Poro-Perm) Transform was used to evaluate the reservoir permeability. The net reservoir and net pay thicknesses were seen attractive in three out of four wells. The reservoir quality parameters “Porosity and Permeability” were different from well to well. The hydrocarbon saturation “Sh” was high in the three wells. The hydrocarbon intervals depths were highlighted and considered in the perforation strategy.     

Anisotropy of permeability,P-wave velocity and electrical resistivity of Upper Cretaceous carbonate samples from Tushka Area,Western Desert,Egypt

Petrophysical properties (such as porosity, permeability, grain density, bulk density, electrical resistivity, and P-wave velocity), as well as the anisotropy of the permeability, seismic velocity (P-wave velocity) and electrical resistivity were characterized in 42 carbonates (limestone) rock samples, collected from shallow wells (seven wells encountered the Upper Cretaceous carbonate rocks with variation in thickness, where well 1 encountered 50 ft thick Nubian sandstone, which decreased to about 30 ft thickness in well 7) from Tushka area, Egypt.The petrographic investigation of the studied carbonate rock samples shows three microfacies associations: Facies1 (MFA-1) is mainly an oolitic, low dolomitic and low glauconitic, fossil-rich packstone with a tendency towards floatstone or rudstone, Facies 2 (MFA-2) is mainly a glauconite rich, low dolomitic floatstone with some tendencies towards rudstone and Facies3 (MFA-3) is mainly a sparry calcite-cemented, low dolomitic rudstone rich in glauconite and iron minerals.The MFA-2 with the lowest average density and highest average porosity is characterized by a strong anisotropy of both permeability and electrical resistivity. The values of the anisotropy ratio of seismic velocity (P-wave velocity) are close to one for all facies, this means that no anisotropy can be detected in the seismic velocity. A comparison between the coefficients of anisotropy reveals that the anisotropy of electrical resistivity and permeability are related to each other.     

The Nature of Pre-Miocene and Miocene Sediments in the Offshore Northern Part of the Gulf of Suez,Egypt

The present study deals with subsurface geology pre-Miocene and Miocene rock units penetrated in the extremely northern offshore Gulf of Suez area. Throughout the pre-Miocene and Miocene, changes in the tectonic pattern, depositional environment, and sediment types indicate different magnitudes and tectonic instability. Based on the available seven dry subsurface composite well logs (GS 9-1, Darag 17-1, GS 24-1, X 80-1, GS 56-1, Fina Z 80-1A, and GS78-1 wells) besides dipmeter logs, 39 stratigraphic maps (isopach and facies maps) are constructed to show thickness variations, facies changes, and paleogeology of Jurassic (Massajid Formation), Lower Cretaceous (Nubia Formation), Upper Cretaceous (Raha, Abu Qada, Wata, Matulla, and Sudr formations), Lower Miocene (Nukhul, Rudeis, and Kareem formations), and Middle Miocene (Belayim, South Gharib, and Zeit formations) times. Moreover, two cross sections are constructed to show thickness and lateral variations in facies changes and tectonics affecting the area at that time. Despite this, the study area has suitable conditions for hydrocarbon generation and accumulation, the seven wells drilled in the study area are considered to be dry or nonproductive. They are considered to be dry or not productive due to tilting of strata to the SW direction, absence of cap rocks (evaporites and salts) and shale in most parts of the study area (especially in the extremely northern parts), and affecting the area by a large numbers of normal faults due to active and continuous tectonic events on the Gulf of Suez area. These reasons may be aided to the migration of hydrocarbons from the area to outside and to the adjacent oil fields.     

河流、沙漠与湖泊沉积环境下形成的层序的对比分析

从不同陆相环境下各种层序地层的发育特征分析入手．探讨了不同类型层序地层——沙漠、河流、湖泊层序地层对比的基础和内容。认为不同陆相环境下各种层序的对比基础是基准面变化,对比内容包括层序的界面特征、层序结构即体系域构成和体系域内沉积体系发育特征．讨论了不同陆相沉积环境下发育的层序地层对比存在的一些问题。     

准噶尔盆地南缘上侏罗统—下白垩统沉积序列及沉积环境演化

准噶尔盆地南缘上侏罗统—下白垩统的沉积相,可以分为曲流河相、冲积扇相、湖水改造冲积扇相和滨浅湖亚相。根据构型要素分析法,划分出10种主要典型岩石相。其中Gm₁为褐红色块状砾岩,复成分,粒度为细—粗砾,分选、磨圆差,主要为杂基支撑;Gm₂为褐色块状砾岩,复成分,粒度为细—中砾,分选和磨圆一般—差,主要为颗粒支撑;Gm₃为灰绿色、橘红色块状细砾岩,分选、磨圆较好,颗粒支撑。Gm₁和Gm₂沉积期,多处发育震积构造。中—晚侏罗世,气候干旱,北天山构造活动,盆地快速充填,可容纳空间减小,上侏罗统齐古组主要发育曲流河沉积。受蒙古—鄂霍次克洋快速闭合的影响,张性环境演变为局部挤压环境,北天山继续构造活动,盆地收缩,可容纳空间减小,盆地边界由早—中侏罗世的中天山退至北天山,上侏罗统喀拉扎组沉积期,准噶尔盆地南缘广泛发育褐红色冲积扇沉积,侏罗纪盆地充填结束;在下白垩统清水河组沉积期,蒙古—鄂霍次克洋闭合完成,构造相对稳定,盆地扩张,可容纳空间增大,大范围快速湖侵,气候转为湿润,准噶尔盆地南缘发育湖水改造冲积扇沉积,之后广泛发育滨浅湖沉积,发育灰绿色、橘红色滨湖砾岩及细粒沉积,白垩纪盆地充填开始。     

Evaluation of the nature,origin and potentiality of the subsurface Middle Jurassic and Lower Cretaceous source rocks in Melleiha G-1x well,North Western Desert,Egypt

The present work aims to evaluate the nature and origin of the source rock potentiality of subsurface Middle Jurassic and Lower Cretaceous source rocks in Melleiha G-1x well. This target was achieved throughout the evaluation of total organic carbon, rock Eval pyrolysis and vitrinite reflectance for fifteen cutting samples and three extract samples collected from Khatatba, Alam El Bueib and Kharita formations in the studied well. The result revealed that the main hydrocarbon of source rocks, for the Middle Jurassic (Khatatba Fm.) is mainly mature, and has good capability of producing oil and minor gas. Lower Cretaceous source rocks (Alam El Bueib Fm.) are mature, derived from mixed organic sources and have fair to good capability to generate gas and oil. Kharita Formation of immature source rocks originated from terrestrial origin and has poor to fair potential to produce gas. This indicates that Khatatba and Alam El Bueib formations take the direction of increasing maturity far away from the direction of biodegradation and can be considered as effective source potential in the Melleiha G-1x well.     

Stratigraphic distribution of the palynomorphs and the particulate organic matter in subsurface Lower/Middle Cretaceous deposits,Western Desert of Egypt: Palynological and geochemical approach

The stratigraphic distribution of the palynomorphs and particulate organic matter was studied in the subsurface Lower/Middle Cretaceous sections in Ii-26-1 and Ig-30-1 wells, located in north Western Desert of Egypt. Some important palynofacies parameters were employed as indicators of proximal–distal trends. The spatial and stratigraphical variations of six palynofacies categories had been illustrated. Optically, the type and nature of the recovered particulate organic matter together with their quantity were combined to reveal the prevailing paleoenvironmental conditions during deposition of the concerning sections. Thirty-seven samples were selected from the two wells to carry the total organic carbon (TOC) and Rock–Eval Pyrolysis analyses in order to geochemically evaluate the source rock.TOC and Rock–Eval Pyrolysis analyses illustrate extremely low TOC and HI values, demonstrating that the Alam El Bueib, Alamein, Dahab, Kharita and Bahariya formations are comprised principally of type IV kerogen and a few type III kerogen components. Therefore, they are inert to slightly gas prone, signifying a strong deficiency of hydrogen-enriched organic matter. Palynofacies analysis implies that all the studied formations have highly oxidized terrestrial organic matter (brown phytoclasts and black woods).     

Burial and thermal history simulation of the subsurface Paleozoic source rocks in Faghur basin,north Western Desert,Egypt: Implication for hydrocarbon generation and expulsion history

Paleozoic Zeitoun, Desouqy and Dhiffah formations represent source rocks to hydrocarbon in Faghur basin, north Western Desert, Egypt. They are characterized by a sufficient amount of organic matter belonging to kerogen type III and mixed type II/III, which are in maturation stage. A 1D-basin modeling was performed by using geological and geochemical data of the Paleozoic source rocks from five wells in Faghur basin, north Western Desert, Egypt. These data used in 1D basin modeling for constructing and understanding of burial and thermal geo-histories of Faghur basin and for simulating and predicting the timing of petroleum and expulsion for the Paleozoic source rocks in the studied wells. Burial and thermal history models indicate that the Zeitoun Formation entered onset of oil generation in the studied wells during Late Cretaceous (100.10–91.65 my) with transformation ratio (TR) 10–25, peak oil during Late Cretaceous (91.65–79.30 my) with TR 25–50 and late oil stage at Late Cretaceous (79.30 my-0) to present day with TR 50–60.45. Desouqy Formation entered onset of oil generation also during Late Cretaceous (94.43–73.60 my) with TR 10–25 in the studied wells, peak oil during Late cretaceous (73.60–62.40 my) with TR 25–50 and Late oil stage during Late Cretaceous to present day (62.40 my-0) with TR 50–61.82. Dhiffah Formation entered onset of oil generation in the studied wells during Early to Late Cretaceous (102.11–92.27 my) with TR 10–25, peak oil during Late Cretaceous (92.27–86.40 my) with TR 25–50 and late oil stage at Late Cretaceous to present day (86.40 my-0) with TR 50–67.27. No cracking oil to gas in the studied Paleozoic source rocks in the studied wells. These basin modeling results also suggest that the Paleozoic source rocks act as an effective source rock where a significant amount of petroleum is expected to be generated and expelled to any nearby prospect reservoir rocks in the Faghur basin.