Investigation of Petrographic and Diagenetic Properties of Asmari Reservoir Cap Rock, SW Iran

Many problems in the production and development of oil fields lie in the correct and accurate assessment of the reservoir cap rock. Ramshir oil field is located 130 km southeast of Ahvaz and is one of the most important oil fields in the southwest of the country. To evaluate the petrographic and diagenetic properties, 300 thin microscopic sections were studied. According to petrographic studies, it was found that the cap rock in Ramshir oil field is composed of more evaporative sediments (mainly anhydrite with some gypsum) with some non-evaporative sediments (marl, carbonate and bituminous shale). The most important diagenetic processes in the study area were considered to be dolomitization, cementation, compaction, anhydrite, recrystallization and substitution. Petrographic and diagenetic studies suggest a swamp-swamp environment for this environment. Lithological changes are a sign of hot, humid, hot and dry weather during sedimentation of the cap rock of this field. Doi: 10.28991/HEF-2021-02-03-06 Full Text: PDF

Interaction Between Mafic Dike Rocks and Salt Deposits in the Rhine Graben, Southwest Germany

ABSTRACT Dikes of primitive olivine melilitites and monchiquites intruded into an Oligocene (Rupelian) potash salt deposit near Buggingen (SW Germany). Ocelli and amygdules reveal distinct mineral assemblages depending on whether the dike rocks are in direct contact with the potash layer or with bituminous shales (Fish Shale). Samples in contact with the potash salt layer show roundish textures that contain smectite ± talc ± chlorite, calcite, and in cases anhydrite and halite, while those close to the bituminous shale mainly comprise smectite, calcite, zeolite group minerals, and analcime. No textural or mineralogical evidence for high-temperature (magmatic) interaction between the dike rocks and the evaporites was observed. This is presumably related to (1) a very low magmatic water activity in the magma, which prevented exsolution of aqueous fluids and appreciable dissolution of the salt, and (2) fast cooling of the magmas, inhibiting melting of the salt deposits and potential liquid mingling and/or assimilation processes. Halite formation in the dike rocks is, rather, related to later, post-magmatic hydrothermal fluids that previously interacted with the salt-rich host rocks. Alteration of the initially glassy groundmass to smectites and zeolites caused an enrichment of Na in the residual fluid, but halite saturation was not attained, as indicated by the absence of groundmass halite. Only fluid–rock interaction in millimeter-sized vugs caused halite precipitation via desiccation by swelling of previously formed clay minerals. Locally, the boron silicate datolite formed in pseudomorphs after olivine. Its precipitation was controlled by the Si and B supply provided by the breakdown of serpentine and smectite.

Kosyu-Rogov Composite Tectono-Sedimentary Element

The Kosyu-Rogov Tectono-Sedimentary Element is one of the last exploration frontiers left in the European part of Russia. Up to 15 km-thick sedimentary section comprises several working petroleum systems. Multiphase structural development created various trapping configurations and numerous reservoir-seal pairs. There are several mature source rocks including the world-class Domanik bituminous shale in the area. The past exploration efforts fell short of delivering expected volumes of oil and gas reserves. This was mainly due to underestimation of technical difficulties related to exploration in the complex tectonic settings and inadequate understanding of the petroleum system development. They were in unfavourable conditions for the reservoir presence and hydrocarbon retention. Revision of the tectonostratigraphic framework of the Kosyu-Rogov CTSE shows new high-impact exploration opportunities. The large petroleum potential of the area is confirmed by the discovery of the Nertseta oil field, the biggest oil find in Russia in 2016.

Geochemical and organic petrographic characteristics of high bituminous shales from Gurha mine in Rajasthan, NW India

A high bituminous shale horizon from the Gurha mine in the Bikaner sub-basin of the Rajasthan District, NW India, was studied using a collection of geochemical and petrological techniques. This study investigated the nature and environmental conditions of the organic matter and its relation to the unconventional oil-shale resources of the bituminous shale. The analyzed shales have high total organic carbon and total sulfur contents, suggesting that these shale sediments were deposited in a paralic environment under reducing conditions. The dominant presence of organic matter derived from phytoplankton algae suggests warm climatic marine environment, with little connection to freshwater enhancing the growth of algae and other microorganisms. The analyzed bituminous shales have high aquatic-derived alginite organic matters, with low Pr/Ph, Pr/n-C17, and Ph/n-C18 ratios. It is classified as Type II oil-prone kerogen, consistent with high hydrogen index value. Considering the maturity indicators of geochemical Tmax (< 430 °C) and vitrinite reflectance values less than 0.40%VRo, the analyzed bituminous shale sediments are in an immature stage of the oil window. Therefore, the oil-prone kerogen Type II in the analyzed bituminous shales has not been cracked by thermal alteration to release oil; thus, unconventional heating is recommended for commercial oil generation.

The recolonisation of volcanically disturbed Eocene habitats of Central Europe: the maar lakes of Messel and Offenthal (SW Germany) compared

To reconstruct the palaeoenvironment and changes within the vegetation, 68 core samples were analysed palynologically from the lacustrine filling of the Eocene maar lake of Offenthal (Hesse, SW Germany). The lacustrine succession includes 16 m of clastic sediments overlain by 13 m of finely laminated bituminous shale. Based on a revised 40Ar/39Ar age of ~ 47.8 ± 0.3 Ma, the lacustrine filling at Offenthal can be dated as uppermost lower Eocene to lowermost middle Eocene which is almost coeval to part of the nearby lacustrine succession at Messel. Cluster and non-metric multidimensional scaling (NMDS) analyses of well-preserved palynomorph assemblages reveal successional stages during the recolonisation of the maar lake and its surroundings which are related to lithological changes. Furthermore, the palynomorph assemblages from Offenthal are compared with assemblages from Messel by NMDS analysis to find similarities and differences during the recolonisation of volcanically disturbed habitats in Central Europe during Paleogene greenhouse conditions. Based on the similar succession in the vegetation at both lakes, four different phases can be distinguished during recolonisation and reestablishment of the vegetation at these sites: (1) an initial phase, (2) a recolonisation phase, (3) a recovery phase, (4) a climax phase.

Glendonite-Like Carbonate Aggregates from the Lower Ordovician Koporye Formation (Russian Part of the Baltic Klint): Detailed Mineralogical and Geochemical Data and Paleogeographic Implications

Stellate and plate-like carbonate bodies, traditionally called anthraconites, are found throughout the Baltic-Ladoga Klint in bituminous shale of the Koporye Formation (Tremadocian, Lower Ordovician). Although this time interval is usually considered as a greenhouse, there is some evidence for the existence of at least temporary cold conditions during the Cambrian–Ordovician. However, the origin of anthraconites is still strongly debated. We studied the mineralogical, petrographic, cathodoluminescence, geochemical, and isotopic characteristics of anthraconites from five sections of the Russian part of the Baltic paleobasin. A close similarity between the morphological, petrographic, cathodoluminescence, and isotopic characteristics of the studied anthraconites with those of glendonites allow us to suggest that these bodies formed in a similar paleo-environment and should be considered as pseudomorphs of the mineral ikaite. The oxygen and carbon isotope ratios reveal that ikaite precipitation occurred in low-temperature conditions on the seafloor. The carbon isotopic values reveal influence of inorganic seawater carbon along with organic matter decomposition and/or methane oxidation during ikaite-glendonite transformations. The oxygen isotopic composition significantly changed after deposition due to meteoric diagenesis. We propose that the studied Tremadocian anthraconites formed under a region of upwelling, where cold phosphate-rich deep waters rose to the relatively shallow part of the Baltic paleobasin, providing favorable conditions for ikaite precipitation. Based on our cathodoluminescence study, we suggest that ikaite was transformed to calcite over several stages during diagenesis. Mineralogical studies also reveal that primary calcite was transformed to sulfate (gypsum) or dolomite during late superimposed processes.

Organic Geochemistry and Source Rock Potential of Naokelekan Formation in Selected Wells, North Iraq

In this study, organic geochemical characteristics and potential of Upper Oxfordian–Lower Kimmeridgian aged bituminous shale beds in Naokelekan formation (North Iraq) were investigated by using TOC and pyrolysis analyses. The Total Organic Carbon (TOC) contents for the studied samples varying between from 0.46-21.33%, average 7.06% and Taq Taq-1 well as good hydrocarbon potential (0.85-1.66 %, with average of 1.06%), whereas Jk-1 well can be rated as an very good hydrocarbon potential from 1.04-4.16 %, with average of 2.15 %. The low Hydrogen Index (HI = 24-605 mg HC/g TOC) for Bj-1 well, (HI = 147-673 mg HC/g TOC) in the Jk-1 well while in Taq Taq-1 well (HI = 9-48 mg HC/g TOC) indicate that kerogen type for the vast majority of the studied samples is Type II/I for Bj-1 well and Type IV with few samples, Type of I and II kerogens in the Taq Taq-1 and Jk-1 well. Consequently most of the organic matter of Bj-1 and Jk-1 well tends to generate petrol, even though a small portion of them exhibit a tendency to generate gas. While all samples of Taq Taq-1 well tends to generate gas. The studied bituminous rock samples characterized by low Tmax (434-602 °C) for Bj-1,Taq Taq-1 (344-429 °C) and (419-602 °C) for Jk-1 well. These values show, in terms of potential of hydrocarbon generation, that the studied samples have a source rock potential of organic matter from immature to over mature. Additionally, the S1 hydrocarbon type values indicate no external contribution of migrated hydrocarbons to the bituminous rocks of the studied area.

Hydraulic fracturing proppants

Hydrocarbon reservoirs can be classified as unconventional or conventional depending on the oil and gas extraction difficulty, such as the need for high-cost technology and techniques. The hydrocarbon extraction from bituminous shale, commonly known as shale gas/oil, is performed by using the hydraulic fracturing technique in unconventional reservoirs where 95% water, 0.5% of additives and 4.5% of proppants are used. Environmental problems related to hydraulic fracturing technique and better performance/development of proppants are the current challenge faced by companies, researchers, regulatory agencies, environmentalists, governments and society. Shale gas is expected to increase USA fuel production, which triggers the development of new proppants and technologies of exploration. This paper presents a review of the definition of proppants, their types, characteristics and situation in the world market and information about manufacturers. The production of nanoscale materials such as anticorrosive and intelligent proppants besides proppants with carbon nanotubes is already carried out on a scale of tonnes per year in Belgium, Germany and Asia countries.