Diagenetic and Depositional Impacts on the Reservoir Quality of the Upper Jurassic Arab Formation in the Balal Oilfield, Offshore Iran

The Kimmeridgian-Tithonian aged Arab Formation, as the main reservoir of the Jurassic succession in the Balal oilfield, located in the offshore region of the Iranian sector of the Persian Gulf, is investigated in this study. The formation is composed of dolomites and limestones with anhydrite interbeds. Based on detailed petrographic studies, six microfacies are recognized, which are classified in four sub-environments including supratidal, intertidal, lagoonal and the high energy shoal of a homoclinal carbonate ramp. The main diagenetic features of the studied succession include dolomitization, anhydritization, cementation, micritization, fracturing and compaction. Based on stable isotope data, dolomitization of the upper Arab carbonates is related to sabkha settings （i.e. evaporative type）. In terms of sequence stratigraphy, three shallowing-upward sequences are recognized, based on core and wireline log data from four wells of the studied field. Considering depositional and diagenetic effects on the reservoir quality, the studied facies are classified into eight reservoir rock types （RRT） with distinct reservoir qualities. Dolomitization has played a major role in reservoir quality enhancement, whereas anhydritization, carbonate cementation, and compaction have damaged the pore throat network. Distribution of the recognized RRTs in time and space are discussed within the context of a sequence stratigraphic framework.

Inspecting the Reservoir Characteristics of the Burgan Formation of Soroosh Oil Field Applying Rock Typing Methods in the Context of Geological Studies

The Albian age Burgan Formation is one of the most important siliciclastic reservoirs in the Arabian Plate. Northwest of Persian Gulf is the main area in Iran invaded by these siliciclastic sediments. This study uses a new and comprehensive procedure to identify the reservoir characteristics of the Burgan Formation in Soroush oil field (NW Persian Gulf). Results from core and petrographic studies led identification of 7 microfacies (MF1 to MF7) that are grouped into 3 main facies association (FA1, to FA3). Results from reservoir characterization indicate a dramatic decrease in reservoir quality from bottom to top (FA1 toward FA3). Using the Flow Zone Indicator (FZI) method, 5 Hydraluic flow units (HFUs) were recognized in the formation. The HFUs are in a notable accordance with facies associations. The HFUs 1 and 2 correlate with theFA1, the HFUs 3 and 4 with the FA2 and the HFU5 cover intervals defined by FA3. Cluster analysis of wireline logs resulted in determination of 5 electrofacies (EF1 to EF5) which are in agreement with the ascertained HFUs. Inspecting the vertical distribution of FAs, HFUs and EFs, three distinct zones are determined. The lower zone is characterized by good reservoir quality, abundance of FA1, HFUs1 and 2 and also EFs 1 and 2 is observed there. The middle zone with a moderate reservoir quality and upper zone presents the poorest quality. In the middle zone FA2, HFUs3 and 4 and also EFs 3 and 4 are more abundant while in the upper one interval are clearly correlated with FA3, HFU5 and also EF5.

An Integrated Appraisal of Burgan Reservoir in Soroosh Oil Field, Using Petrographic and Petrophysical Approaches

The Burgan Formation in northwest of the Persian Gulf is applied to lower part of Albian age Kazhdumi Formation, where is dominated by coarse to medium terrigenous facies. It is the most susceptible siliciclastic unit in the area to hydrocarbon reservoir. This reservoir is studied in a well of Soroosh oil field with best available data to determine its facies characteristics, sequence stratigraphy and reservoir quality. Based on the petrographic results and log data, 7 facies are determined in the formation, which are mainly composed of sandstone and shale. These facies are classified into three facies associations (FA) based on their sedimentological properties and environmental conditions. The first FA consists of sandstone, siltstone and shale, mostly developed in the lower part of formation, and is related to a fluvial environment. The second FA consists of fluvial sandstones and sandwich by marine shales and is related to fluvial-dominated shallow marine setting (estuary to delta). The third FA consists of limestones of chemical and biochemical origin and is related to a marine condition. According to their reservoir quality, these facies associations show a decreasing trend in porosity and permeability values from FA1 to FA3. The first FA is more abundant in the lower part of the Burgan Formation where causes a good reservoir quality trait. FA2, presenting a medium reservoir quality, is more frequent in the middle parts of studied formation and FA3 is found almost in the upper parts. Based on the results from this study, three 3rd order sequences have been identified. Sequences 1 and 3 are partial but the sequence 2 is the main and most complete one of the formation in the studied area. The paleosol horizons are used for relative sea level change analysis of the formation in sequence stratigraphic studies.

Effect of alumina and silica nanocomposite based on polyacrylamide on light and heavy oil recovery in presence of formation water using micromodel

Increasing world request for energy has made oil extraction from reservoirs more desirable.Many novel EOR methods have been proposed and utilized for this purpose.Using nanocomposites in chemical flooding is one of these novel methods.In this study,we investigated the impact of six injection solutions on the recovery of light and heavy oil with the presence of two different brines as formation water using a homogenous glass micromodel.All of the injection solutions were based on a 40,000 ppm Na Cl synthetic seawater(SSW),one of which was additive free and the others were prepared by dispersing nanocomposite silica-based polyacrylamide(NCSP),nanocomposite alumina-based polyacrylamide(NCAP),the combination of both nanocomposites silica and alumina based on polyacrylamide(NCSAP),surfactant(CTAB)and polyacrylamide(PAM)with a concentration of 1000 ppm as additives.The Stability of nanocomposites was tested against the salinity of the brine and temperature using salinity and DSC tests which were successful.Alongside stability tests,IFT,contact angle and oil recovery measurements were made.Visual results revealed that in addition to the effect of silica and alumina nanocomposite in reducing interfacial tension and wettability alteration,control of mobility ratio caused a major improvement in sweeping efficiency and oil recovery.According to the sweeping behavior of injected fluids,it was found that the main effect of surfactant was wettability alteration,for polyacrylamide was mobility control and for nanocomposites was the reduction of interfacial tension between oil and injected fluid,which was completely analyzed and checked out.Also,NCSAP with 95.83%and 70.33%and CTAB with 84.35%and 91%have the highest light oil recoveries at 250,000 ppm and 180,000 ppm salinity,respectively which is related to the superposition effect of interactions between nanocomposites,solution and oil.Based on our results it can be concluded that the most effective mechanism in oil recovery was IFT reduction which was done by CTAB reduction also by using a polymer-based nanocomposite such as NCSAP and adding the mobility control factor,the oil recovery can be further enhanced.In the case of heavy oil recovery,it can be concluded that the mobility control played a much more effective role when the PAM performed almost similarly to the CTAB and other nanocomposites with a recovery factor of around 17%.In this study,we tried to investigate the effect of different injection solutions and their related mechanisms on oil recovery.

Provenance and Tectonic Setting of Late Lower Cretaceous (Albian) Kazhdumi Formation Sandstones (SW Iran)

Provenance and tectonic setting of the Late Lower Cretaceous (Albian) sandstones in SW Iran have been interpreted on the basis of geochemistry (major and trace elements) of 35 samples from Iranian offshore oil fields (Soroosh, Nowrooz, Foroozan and Hendijan). Geochemically, trace-element concentrations, such as La, Th, Sc and Zr, and ratios, such as La/Sc, Th/Sc, La/Co, and Th/Co, of sandstones from Kazhdumi Formation at four localities indicate that they were derived from felsic source rocks and deposited in a passive continental margin. Most major and trace element contents of Kazhdumi sandstones are generally similar to upper continental crust (UCC) values. However, some samples are depleted in major and trace elements (such as K2O, Na2O, Sr and Ba) relative to UCC, which is mainly due to absence or smaller amount of Na-rich plagioclase and K-feldspar and also paucity of clay minerals, which is possibly due to intense weathering and recycling. Enrichments in Zr, negative Sr anomalies and Th/U ratios higher than 4 for Kazhdumi sandstones are further evidence for recycled sources. The study of paleoweathering conditions based on chemical index of weathering (CIW) indicates a moderate to intense weathering of first cycle sediments, or it may alternatively reflect recycling under semi-arid to semi-humid climate conditions in Kazhdumi sandstones. The results of this study suggest that the main source for the Kazhdumi sandstones is likely located in uplifted shoulders of a rifted basin (Neo-Tethys) in its post-rift stage (Arabian basement).

Case study of hydraulic fracturing in an offshore carbonate oil reservoir

Maximizing petroleum production while efficiently managing the operational costs is the oil and gas industry's primary goal which requires innovative engineering approaches and production-enhancing treatments such as hydraulic fracturing(HF).During the HF process,the injected fluid mixed with sands or proppants will create permanent fluid channels to drain more of the reservoir volume.The level of complexity and various constraints involved in real field treatments have made HF even more chal-lenging in layered carbonate reservoirs with the water drive mechanism.A prominent concern is the downward fracture growth to the oil/water contact zone that may cause unfavorable water cut levels.This fracture height confinement criterion necessitates optimization of fracture dimension design.Fracture height development is mainly a function of in-situ stress conditions and stress magnitude differences between geologic layers.In cases with a water table at the proximity of the wellbore,fracture height directly affects the operational success.This paper demonstrates a practical step-by-step approach towards the design of hydraulic fracturing treatment in an offshore carbonate oil reservoir.The modeling process involves optimization of the location,number,and conductivity of the proposed fractures.In-jection of high viscosity fluid causes a bi-wing vertical planar fracture to propagate perpendicular to the direction of minimum horizontal stress in the strike-slip faulting regime.Dimensions of the induced hydraulic fractures are also impacted by the amount and type of proppants.However,as with this case study,the magnitude of vertical stress is in the same range as the maximum horizontal stress;the fracture height growth is the limiting factor.The LGR method is used to define fractures in the dynamic reservoir model which has been built based on a complete set of data ranging from the analyses of logs,core samples,and seismic details,to perform production forecasts and economic evaluation.Then a hydraulic fracture software is implemented to provide a timetable for fracturing fluid volume and mixing proppant concentration for the desired fracture dimensions.The results show that,despite the operator's previous perception,five hydraulic fractures per well would be economical,which include a 150 ft long fracture and four shorter fractures with an approximate length of 75 ft designed to manage the risk of penetration into the water-bearing formations.Due to the reservoir pressure drop by time and more flexible fracture dimension constraints at earlier stages of production,executing such stimulations earlier than later would improve the commercial outcomes.

A CMOS 3.1 - 10.6 GHz UWB LNA Employing Modified Derivative Superposition Method

Low noise amplifier (LNA) performs as the initial amplification block in the receive path in a radio frequency (RF) receiver. In this work an ultra-wideband 3.1 10.6-GHz LNA is discussed. By using the proposed circuits for RF CMOS LNA and design methodology, the noise from the device is decreased across the ultra wide band (UWB) band. The measured noise figure is 2.66 3 dB over 3.1 10.6-GHz, while the power gain is 14 ± 0.8 dB. It consumes 23.7 mW from a 1.8 V supply. The input and output return losses (S11 & S22) are less than –11 dB over the UWB band. By using the modified derivative superposition method, the third-order intercept point IIP3 is improved noticeably. The complete circuit is based on the 0.18 μm standard RFCMOS technology and simulated with Hspice simulator.

Sedimentology and depositional environment of the Kazhdumi Formation Sandstones in the northwestern area of the Persian Gulf

Kazhdumi is one of the Bangestan Group formations aging late early Cretaceous (Albian). Three subsurface sections of the sandstone bearing part of Kazhdumi in the studied area located at northwest of the Persian Gulf are assessed for determining sedimentary facies and depositional environment. Based on the recognized facies, the sandstone bearing zones of Kazhdumi and their relevant paleoenvironments can be addressed as: first one is the B sandstone zone containing thick sandstone layers alternating with shale and siltstone thin layers which are deposited by river influenced conditions because of the characteristics like: cross bedding, oxidized constituents and palesol. The second one, the A sandstone zone which is deposited under a key limestone layer, is composed of sand/sandstone layers with marine features and presents the interaction of marine-river condition in deltaic channels. This zone, is a transition interval showing the changes of river-dominated condition to marine one. The third one is the A sandstone zone deposited above the key limestone layer containing fine grained laminated siliciclastic and chemical sediments. Alternation of distal channel facies and green marine shale of delta containing glauconite, pyrite and organic matter residuals, all confirm the reduction condition in estuarine environment. Applying facies analyses results, isopach maps, porosity distribution maps and sandstone grain size study, the paleocurrent pattern is determined from the southwest to northeast.