Zakaria, Hasan (ADNOC Offshore) | Al-Hammadi, Mariam (ADNOC Offshore) | Lehmann, Christoph (ADNOC Offshore) | Al-Hassani, Sultan (ADNOC Offshore) | Ahmed, Shafiq (ADNOC Offshore) | Khan, Owais (ADNOC Offshore) | Al-Ali, Ahmed (ADNOC Offshore)
A sedimentological study of an Offshore, mid-Jurassic reservoir was carried out in order to understand reservoir quality and reservoir architecture. In-house core description, and analysis of open-hole petrophysical log interpretation and conventional core analysis, enabled the authors to interpret the depositional environment and produce hand drawn facies maps to understand the facies architecture; by developing facies scheme, depending of depositional environment comingled with diagenetic process.
About 2,285 ft of core and 1,799 thinsections were described from 18 wells, distributed throughout the field. Description of core was done at 1:50 scale and about 495 thinsections were pictured throughout the reservoir section. Detailed description of textural and faunal content, along with sedimentary features was carried out to determine the depositional model and facies architecture. By analyzing the diagenetic features and porosity type, Reservoir Quality controls were derived. All these elements were taken into consideration in order to build facies scheme that not only justifies the depositional environment but also incorporates the impact of diagenesis.
A low relief, very active shoal system on a giant carbonate platform was interpreted. Various Lithofacies were grouped into 5 Facies associations keeping in mind depositional environment and diagenetic impact. This model was used to make 4 hand drawn facies maps representing reservoir X and High permeable layer, X7 with general tendency of better facies in the northern part of the field.
The novelty of this work is the differential degree of cementation due to the abundance of echinoderms degrading the reservoir quality, and identifying these dominant echinoderm facies zones allows us better well placement by avoiding them.
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The Vaca Muerta Formation (Neuquén Basin) is a world class Shale reservoir that covers oil, condensate and gas windows, with more than 300 horizontal wells drilled in the whole basin. This case study is located in the Shale Oil window that includes 30 horizontal wells on production, in a zone characterized by a huge areal and lithological variability due to the nature of the mix carbonate-siliciclastic depositional system. The main objective of this work is to characterize petrophysical and sedimentological properties of Vaca Muerta Fm. at log resolution to visualize and adjust the landing zones, relate to well productivity and extrapolate this information to a static model.
Logs and core integration workflows allowed to obtain 11 electrofacies honoring the composition and texture of the formation. The electrofacies composition is calculated from the basic electrical logs (Gamma Ray, Density, Photoelectric Factor and Compression Sonic) and interpreted kerogen volume, while the textural component was imposed by working the supervised electrofacies models with the sedimentological description of the rock. Subsequently, each electrofacies was assigned petrophysical properties such as porosity and water saturation from well logs calibrated with laboratory data.
The Vaca Muerta Formation consists primarily of a mixed carbonate-siliciclastic basinal facies in the largely progradational Quintuco-Vaca Muerta system. There are between 150-450 meters of organic-rich strata, all of which have the potential to produce, but there is also significant vertical and lateral heterogeneity related to the intercalation of different lithologies, the clinoform geometry and areal position. A better understanding of the reservoir characteristics of each of these facies, their distribution and their link to petrophysical properties is a key variable to select the best landing zones to develop the area.
The main findings of this study are: i) electrofacies model shows that organic content (electrofacies E7-E11) and porosity increases north and northwestwards for all LZ, ii) the mineral proportion for each electrofacies varies within the depositional system position (e.g. carbonate content increases southeastward, iii) in general, best productive wells are related to better electrofacies, iv) Electrofacies E1 & E2 (low TOC) show higher Sw and low TOC, while E7-E11 exhibits lower Sw, v) the model highlights new upside opportunities with additional hydrocarbon potential, vi) the geological and electrofacies model allowed to improve the understanding on the depositional system that will help to build robust paleoenvironmental maps.
Rudists are a group of strange shaped marine bivalves lived in the Tethys Ocean from the Late Jurassic to the Late Cretaceous. The rudist-bearing carbonates form a lot of oil and gas reservoirs in the Middle East. Therefore, the taxonomy, morphology, paleo-ecology of rudists is important to understand the rudist-bearing carbonate reservoir features for oil exploration and development. However, it is difficult to understand these characters of rudists because we can't collect whole rudist samples from the underground oil and gas reservoirs through core sample. X-ray CT is a useful method to visualize three dimensional rudist images with non-destruction of the core. Hence, X-ray CT has a potential to obtain the information of the taxonomy, morphology and depositional environment of rudists from core information. We conducted the X-ray CT scan to the reservoir formation (Formation A) of the Cenomanian age using core slab samples of Well #A and Well #B in the Abu Dhabi oil field. The some rudist fossils were observed on the cutting surfaces of slab cores in the both wells. However, the three dimensional morphology of rudists were not identified inside of the slab core. On the CT images, some autochthonous rudists were identified and it made the colony in Well #A. This rudist is standing position and suggesting original position of depositional environment from
Al-Enezi, Bashar (Kuwait Oil Company) | Kostic, Boris (Badley Ashton & Associates Ltd) | Foote, Nicolas (Badley Ashton & Associates Ltd) | Filak, Jean Michel (Kuwait Oil Company) | Al-Mahmeed, Fatimah (Kuwait Oil Company) | Al-Shammari, Obaid (Kuwait Oil Company) | Bertouche, Meriem (Badley Ashton & Associates Ltd)
Resistivity image logs are high-resolution tools that can help to unravel the depositional and structural organisation in a wellbore. They provide a particularly powerful dataset when calibrated against core, maximising their benefit for reservoir characterisation. This paper shows examples how very detailed image assessment from selected wells in the Greater Burgan Field has helped to constrain the stratigraphic model and depositional interpretations of the Cretaceous Burgan and Wara reservoirs.
A multidisciplinary study of 123 cored wells, integrating core sedimentology, petrography, bio- and chemostratigraphy, wireline well and resistivity image logs, has delivered a robust stratigraphic and depositional framework for one of the most important reservoirs in the world's largest siliciclastic oil field. A descriptive image facies scheme that has been calibrated against core and conventional well logs captures the lithological variation, sedimentary features and surfaces of the reservoir, providing a detailed proxy for the sedimentological evaluation of uncored intervals and wells.
The sand-rich lower Burgan (4S) comprises fine to very coarse-grained fluvial channel sandbodies that are locally separated by laterally restricted mudrock baffles. Image and core analyses suggest that the majority of the sandstones are high-angle cross-stratified and form stacked barforms within amalgamated channel sandbodies. Their consistent orientation towards the NE-E supports a low-sinuosity (braided) fluvial system resulting in a relatively simple, sheet-like depositional architecture across the field. Although slightly finer grained, the cored middle Burgan channel sandbodies (3SM) are similar to those in the lower Burgan. However, palaeoflow data from the imaged wells show a higher directional spread in the order of
The examples from the Burgan and Wara Formations highlight the value of integrated image analysis for reservoir characterisation by delivering a consistent descriptive framework, embedding different datasets.
The PDF file of this paper is in Russian.
The present paper describes the results of analysis of depositional environment and tectonic setting in South - East part of the Pre-Caspian basin. The main purpose of the study is generalization and interpretation of geological and geophysical data for creation of stratigraphic chart, description of lithological and tectonic processes for reconstruction of the structural history of pre-salt perspective traps, located in close vicinity to Tengiz field.
It is known quotation that carbonates are born, not made, hence, their characteristics can give an insight into their depositional environment. Such factors as availability of the light, warm climate, chemical composition and transparency of the water altogether define the growth of the reef-building organisms. Highest carbonate production take place close to the water surface, therefore, facies and texture of carbonates may be linked to the sea level changes. It means that understanding of the depositional environment and sequence stratigraphy may be used for reservoir description, where no data is available.
For understanding of tectonic processes, analysis of seismic reflectors was carried out. Shallowest depth on top of carbonates is observed on Tazhigali - Pustynnaya structure, gradually deepening towards Ansagan and Maksat to the south, southeast. Also, III and V reflective horizons in post-salt deposits has inclined surface from the north to the south.
Tectonic deepening in south, southeast direction took place in several stages. The first stage, most probably, took place in Late Devonian – Early Carboniferous age, when Ansagan and Maksat structures were drowning. At the northern part of the Karaton-Tengiz uplift, the growth of reefs continued up to Late Carboniferous. Seven supersequence boundaries, interpreted on Tengiz carbonate platform, also predicted to be present on Tazhigali - Pustynnaya.
For the better understanding of the difference in depositional environment and tectonic setting, the thickness of structures and inclination degree of interpreted horizons were compared. Well logging interpretation and published papers were integrated whenever possible. As the result, conceptual model of structural history and stratigtaphic charts were created for the studied region.