Thickness record of varves from glacial Ojibway Lake recovered in sediment cores from Frederick House Lake, northeastern Ontario

The thicknesses of 384 rhythmic couplets were measured along a composite sequence of glacial Lake Ojibway glaciolacustrine deposits recovered in two sediment cores from Frederick House Lake, Ontario. The visual comparison of distinctive couplets in the CT-scan radiographs of the Frederick House core samples to photographs of core samples from Reid Lake show a match of ±1 varve number from v1656-v1902, and ±5 varve numbers between v1903-v2010, relative to the regional numbering of the Timiskaming varve series. There are two interpretations for the post-v2010 couplets that fall within the Connaught varve sequence of the regional series. In the first, the interpreted numbering spans from v2066-v2115, which produces a gap of 55 missing varves equivalent to v2011-v2065, and corresponds to the original interpretation of the Connaught varve numbering. The second spans v2011a-v2060a, and represents alternative (a) numbering for the same varves. Varve thickness data are listed in spreadsheet files (.xlsx and .csv formats), and CT-Scan radiograph images of core samples are laid out on a mosaic poster showing the interpreted varve numbering and between-core sample correlations of the varve couplets.

Integrated Assessment of Marine-Continental Transitional Facies Shale Gas of the Carboniferous Benxi Formation in the Eastern Ordos Basin

In the Benxi Formation of the Carboniferous system of the Upper Paleozoic in the Ordos Basin, there are many sets of coal measures dark organic-rich shale, being marine continental transitional facies, with significant unconventional natural gas potential. Previous studies are only limited to the evaluation of tight sandstone reservoir in this set of strata, with no sufficient study on gas bearing and geological characteristics of organic-rich shale, restricting the exploration and evaluation of shale gas resources. In this study, analysis has been conducted on the organic carbon content, the major elements, the trace elements, and the mineral composition of core samples from the Benxi Formation in key drilling sections. In addition, qualitative and quantitative pore observation and characterization of core samples have been conducted. The sedimentary environments and reservoir characteristics of the shale of the Benxi Formation have been analyzed. Combined with the gas content analyzing the results of the field coring samples, the shale gas resource potentials of the Benxi Formation have been studied, and the geological characteristics of the Benxi Formation shale gas in the eastern Ordos Basin have been made clear, to provide a theoretical basis for shale gas resource evaluation of the Benxi Formation in the Ordos Basin. The results show that (1) in the Hutian Member, Pangou Member, and Jinci Member of the Benxi Formation, organic-rich shale is well developed, with the characteristics of seawater input as a whole. There is a slight difference in sedimentary redox index, which shows that the reducibility increases gradually from bottom to top. (2) There is an evident difference in the mineral characteristics of shale in these three members. The Hutian Member is rich in clay minerals, while the Jinci Member is high in quartz minerals. (3) The pores are mainly inorganic mineral intergranular pores, clay interlayer fractures, and micro fractures, and organic matter pores are developed on the surface of local organic matter. (4) The mud shale in the Jinci Member has a large cumulative thickness, has relatively high gas-bearing property, and is rich in brittle minerals. The Jinci Member is a favorable section for shale gas exploration of the Benxi Formation.

Investigation of Oil Presence and Wettability Restoration Effects on Sulfonated Polymer Retention in Carbonates Under Harsh Conditions

Polymer flooding in carbonate reservoirs is greatly affected by polymer retention, which is mainly due to polymer-rock surface interactions. Consequently, this leads to a delay in polymer front propagation and related oil recovery response. This work investigates the effect of oil presence and wettability restoration on polymer retention under harsh reservoir conditions of high temperature and high salinity (HTHS). An ATBS-based polymer was used for this study. Polymer single- and two-phase dynamic retention tests as well as bulk- and in-situ rheological experiments were conducted on Indiana limestone outcrops and in the presence of high salinity brine of 243,000 ppm at temperature of 50 °C. A total of four coreflooding experiments were conducted on core samples with similar petrophysical properties. Bulk rheology tests showed that the polymer is stable at HTHS conditions. Also, polymer retention and in-situ rheology tests highlighted the significance of oil presence in the core samples where retention was found to be around 40-50 and 25-30 μg/g-rock in the absence and presence of oil, respectively. An additional 50% reduction in retention was further observed on a restored wettability (aged) core sample. Polymer inaccessible pore volume (IPV) was found to be high in the range of 23 to 28%, which was supported by the 1D saturation profiles obtained from the CT scanner. The ATBS-based polymer shows excellent results for applications in carbonates under harsh conditions without considerable polymer loss or plugging. This paper also provides valuable insights into the impact of oil presence and wettability restoration on polymer retention. Furthermore, this study shows that careful consideration of the latter factor is necessary to avoid unrepresentative and inflated polymer retention values in oil reservoirs.

Delineating Weak Zones in Limestone based on Borehole Drilling and Electrical Resistivity Tomography

This study is focused on imaging of weak zones in subsurface using borehole and geophysical datasets. These weak zones are present within Jhill limestone of Miocene age across the northern, Karachi. A total of forty-nine core samples were collected from eleven boreholes about 30 m deep within the study area. The core analysis reveals presence of cavities in fractured limestone at shallow and deep levels. The lateral extension and thickness of these weak zones are well imaged by the electrical resistivity tomography (ERT) dataset. The 2D tomographs of the six profiles show variability in the ground resistivity response. The ERT profiles are interpreted using on hand samples collects from boreholes. These tomographs reveal relatively high resistivity values interpreted as intercalation of dry clay and marl beds within limestone. The medium resistivity values suggest presence of clay and sand in highly fractured limestone or surficial dry features. The low resistivity values are interpreted to be originated 24 by the weak zones filled with lithologies having high moisture content within limestone. The collected core samples were analysed for geotechnical parameters. The integration of borehole and ERT datasets delineated weak zones in the northern and central regions, which should be well28 cemented to avoid any geohazard.

Factor analysis of the geochemical associations in the Plavica ore deposit, Republic of North Macedonia

The aim of this study is to investigate the geochemical associations in the Plavica deposit in Republic of North Macedonia. The analyses of drill core samples from the detail exploration works were statistically processed to determine the groups of chemical elements with common spatial distributions. The resulting geochemical groups represent different stages of the ore forming hydrothermal processes. The main ore elements are represented by geochemical association of ([As, Sb, Au, Sn] Cu, Bi, Fe, Ag) which group outlines the ore bodies.

Petrophysical Properties Estimation of Euphrates Reservoir in Qayyarah Oil Field Using Core and Well Log Data

The Early Miocene Euphrates Formation is characterized by its oil importance in the Qayyarah oil field and its neighboring fields. This study relied on the core and log data analyses of two wells in the Qayyarah oil field. According to the cross-plot’s information, the Euphrates Formation is mainly composed of dolomite with varying proportions of limestone and shale. Various measurements to calculate the porosity, permeability, and water saturation on the core samples were made at different depths in the two studied wells Qy-54 and Qy-55. A relationship between water saturation and capillary pressure has been plotted for some core samples to predict sites of normal compaction in the formation. The line regression for this relationship was considered as a function of the ratio of large voids to the total volume of voids in the sample. The coefficient of determination parameter was used in estimating the amount of homogeneity in the sizes of the voids, as it was observed to increase significantly at the sites of shale. After dividing the formation into several zones, the well log data were analyzed to predict the locations of oil presence in both wells. The significance of the negative secondary porosity in detecting the hydrocarbon sites in the Euphrates Formation was deduced by its correspondence with the large increase in the true resistivity values in both wells. More than 90% of the formation parts represent reservoir rocks in both wells, but only about 75% of them are oil reservoirs in the well Qy-54 and nearly 50% of them are oil reservoirs in the well Qy-55.

Automation of technological processes in the examination of core samples

Currently, there are quite serious problems in the methodology of conducting petrophysical studies. These problems have a significant impact on the process profitability of obtaining analysis results. Improving the efficiency of laboratory analyses is an important direction towards enhancement of the methodological approaches used in the laboratory practice. Automation of the process of recording the volume of water displaced from the chamber of a group capillarimeter while determining the water saturation of standard and full-size core samples is analyzed.

Deformations of weakly lithifed rocks of the Bazhenov-Georgievsky complex

Research subject. Deposits of the Upper Jurassic Bazhenov-Georgievsky complex situated in central West Siberian regions. At a frst approximation, the deposits are represented by interlayering pure or carbonatized radiolarites and organic-clay mixites. Materials and methods. A collection of core samples taken from the deposits was analyzed to study the geological and geophysical features of borehole sections, photographs of core samples, and micrographs of thin section. Soft sediment deformations, which appeared within the Bazhenov-Georgievsky complex as a result of earthquakes, were investigated using data obtained by Chinese researchers. Results. It is shown that, at different stages of diagenesis, layers with sharply differing density and mechanical properties came into contact, which led to various deformations of weakly lithifed layers during earthquakes. In the early and middle diagenesis, mobile carbonated radiolarites deformed plastic clay interlayers with the formation of carbonate nodules. In the middle diagenesis, in radiolarites, areas of weak lithifcation and mobile radiolarites coexisted. Along with plastic deformations, the processes of autobrecciation and autofluid fracturing of radiolarites, abrasion erosion of the boundaries of clayey varieties took place. In the late diagenesis, lithifed varieties predominated in radiolarites and clayey silicites; as a result of deformations, radiolarites and the argillaceous bridges separating them were transformed into fragments, polished surfaces, and pellets. If, under the influence of differential loads, fluidization (softening) and movement of weakly lithifed radiolarites occurred, then the rates of such movements in adjacent layers inevitably differed. Each of the described cases is demonstrated by the core material of specifc boreholes and petrographic thin sections. The scale of the phenomenon is shown from the signs of loading of millimeter interlayers to pressure shafts of brecciated limestones with a thickness of 7–10 m. Conclusions. The West Siberian Plate is epicontinental; therefore, the most intense earthquakes occurred at consolidated basement block boundaries during isostatic subduction and compensations in the Neocomian clinoform ultrafast sedimentation zones. Soft sediment deformations occurred within the Bazhenov-Georgievsky layers recorded the rock history of intense seismic events of the past, their temporary and spatial distribution.