Shale-gas potential from Cretaceous succession in South Africa’s orange basin: insights from integrated geochemical evaluations

Shale sediments were collected from four Cretaceous stratigraphic units across four explorations well locations in South Africa’s Orange Basin and analysed to determine organic-matter characteristics, such as amount, quality, thermal maturity, and their viability as gas resources. The geochemical results show that the Cretaceous shales contain moderate organic quantities, as shown by TOC averagely up to 1.29%. The organic facies consist primarily of Type III kerogen, as proven alongside low hydrogen indexes between 40 and 133 mg HC/g TOC. As seen under a reflected light microscope, the dominance of such land plant-rich organic matter is in harmony with the significant amount of Vitrinite macerals. These organic sediments can produce primarily gas when they mature. The geological and geochemical properties of the organic sediments, chiefly Type III kerogen, generate both wet and dry gas, particularly when adequate thermal maturity is enhanced at deeper locations. Thus, the Orange Basin is considered promising for shale gas exploration and production

Characterization and impact of peat fires on stabilization of tropical lowland peats in Banting, Selangor, Malaysia

Peat soil is a representative material of soil and well known as rich in organic matters, high compressibility, high porosity and low shear strength. During dry seasons, peat lands will lose lots of water and potentially turn into a tinderbox bringing in fires. When peat forest fires happen, it prompts degradation of humic-rich organic matter eventually reduce the stability of peat soil. The impacts of peat fire on peat soil from degraded area in Banting, Selangor, Peninsular Malaysia, were investigated through the field identification, physical and engineering properties through burnt peat site. The Unconfined Compressive Strength (UCS) result shows the burnt peat soil gained in strength that strongly related to the binder and filler dosage, moisture content of peat and curing time. The value of UCS strength increased with the gain of moisture content of peat samples but the strength tends to decrease when the moisture content exceeds certain point. The organic material changed its physical and chemical structure resulting from the fire event, thus, the capability of the soil to hold water particles is reducing and yielded higher UCS strength of cement-peat-stabilization. The most important geotechnical aspects of peat that have effect on stabilization process are natural water content, humification grade, ash content, and pH value. The results also suggested that lateral variation within the peat basin indirectly affects the strength of cement-peat-stabilization. The strength of burnt peat can be considerably improved by stabilization and support the concept of Air Curing Technique

Pyrolysis analyses and bulk kinetic models of the Late Cretaceous oil shales in Jordan and their implications for early mature sulphur-rich oil generation potential

In this study, oil shale samples were collected from Late Cretaceous Muwaqaar Chalk Marl Formation (MCM) in Jordan to study their petrologic and organic geochemical properties. Pyrolysis and bulk kinetic techniques were performed on the Late Cretaceous oil shales. The results of this study were used to characterize the different organofacie types in the Late Cretaceous oil shales and their effect on the petroleum type generated during thermal maturation and the temperature of petroleum generation. On the basis of the geochemical results, the analysed Late Cretaceous oil shales contain predominantly Type II and rarely Type I kerogens. These kerogens are consistent with the high dominate of sapropel organic matter (i.e., alginite and amorphous organic matter). A good correlation is noted between increasing abundance of organic matter and the kerogen type that was derived from an open pyrolysis–gas chromatography (Py–GC). The Py–GC data indicate the analysed oil shale samples contain heterogeneous organic matter of the kerogen Type II-S. It is interesting to know that this sulphur-rich kerogen (Type II-S) can generate high sulphur oils at low maturity ranges. This is consistent with the predicted temperature petroleum generation from bulk kinetic models. The bulk kinetic models in this study indicate that the main phase of petroleum formation from the thermally immature Late Cretaceous oil shales occur between 122 and 148 °C. These temperature values of the petroleum generation are generally consistent with the kerogen type II-S and further indicate that the analysed oil shale samples can generate sulfur-rich oils at early stage of kerogen cracking

Effects of maturity on the pyrolytic fingerprint of coals from North Borneo

Pyrolysis-gas chromatography-mass spectrometry (Py-GC–MS) and thermally assisted hydrolysis and methylation (THM-GC–MS) were applied to 27 coal samples of lignite to high volatile bituminous rank (vitrinite reflectance %Ro = 0.28–0.66) from the Malaysian states of Sabah and Sarawak on Borneo, to investigate rank effects on molecular properties. The molecular fingerprints of these coals appeared to be controlled by diagenetic and, to a smaller extent, early catagenetic transformations (%Ro 0.28–0.50). The molecular assemblages from immature coals consist mainly of lignin-derived material and long-chain (≥ C24) ester-bound polymethylene chains, whereas mature coals are enriched in short (C10–C25) free and/or trapped (isoprenoid) hydrocarbons, alkylated phenols and resinite aromatic derivatives. By comparing a large suite of potential molecular proxies of maturation (indices of pristane formation, resin aromatization, lignin alteration stages, etc.) and other maturity proxies (%Ro, Tmax), rank effects on different coal constituents are illustrated, as well as the suitability of the proxies for specific rank ranges. The results highlight the importance of decarboxylation of long-chain fatty acids (%Ro 0.35–0.40) and the progressive accumulation of resistant aryl-O (probably diaryl ether) bonds at advanced stages of maturity. The coals from Pinangah in Sabah were more mature than those from Sarawak (Mukah and Balingian coalfields), whereas the molecular signature of other coals from northeastern Sabah (Sandakan area) and southeastern Sabah (Silimpopon and Maliau areas) varied across the rank range studied.This study was partially financed through grants RP002C-13AFR and FP042-2013A. We are grateful to Klaas Nierop (Utrecht University) for valuable discussions on FAMEs patterns and to the anonymous reviewers for their insightful comments.Peer Reviewe

Paleoenvironmental reconstruction and hydrocarbon potentials of Upper Cretaceous sediments in the Anambra Basin, southeastern Nigeria

Palynological, organic petrographic, and organic geochemical analyses of the Campanian-Maastrichtian sediments in Akukwa-2 well were carried out to infer their paleoenvironments, origin of the organic matter, and hydrocarbon generation potentials. The TOC values of the analysed sediments range from 0.27–3.02 wt%, while the S2 pyrolysis yield range from 0.55 to 3.35 mg HC/g rock. This indicates that the Nkporo and Mamu sediments possess fair source generative potential. The samples contain Type III-II and Type III kerogen as shown by the present-day HI values between 58 and 292 mg HC/g TOC and pyrolysis-GC data. The organic matter within the sediments is also likely to generate mainly gas. This is in agreement with the petrographic observations, which revealed that the analysed shale samples contain abundant vitrinite macerals, apart from bituminite, alginite, cutinite, and resinite. Also, the sediments are immature to early mature in terms of hydrocarbon generation as indicated by vitrinite reflectance, biomarker maturity, and pyrolysis Tmax data. Biomarker distribution ratios, palynomorphs assemblage, and organic petrographic observations further point out that the organic materials within the sediments were of mixed aquatic and terrigenous origin and were deposited under suboxic paleodepositional conditions. Based on sedimentological, palynological, and biomarker characteristics, the environment of deposition of the analysed sediments was inferred to be a relatively quiet, shallow marine with fluvial incursion, most especially at the upper part of the intervals studied and consequently, it is a delta associated depositional environment with a fluviatile influence. The sediments are therefore suggested to be deposited in a paleogeographic setting close to vegetation source

Critical rate analysis for CO2 injection in depleted gas field, Sarawak Basin, offshore East Malaysia

This study aimed to address the challenges and strategies to determine the critical rate of CO2 injection into a carbonate depleted gas field. In this research, the critical rate is the maximum allowable injection rate before formation damage initiation. The cause of formation damage could be due to in-situ mobilization or trapping of migratory fines resulting in plugging the flow path. This study performed a thorough investigation of a different rock-fluid system to evaluate the safe injection limit, as the critical rate is different for each rock-fluid system. The geochemical effect of CO2 injection toward carbonate formation was also investigated in this research. Other than that, the porosity and permeability changes due to CO2-brine-rock multiphase flow characteristics were considered to understand the feasibility of CO2 sequestration into carbonate formation. This research discussed experimental design to mimic the CO2 injection scenario of CO2 into carbonate depleted gas field. Therefore, several core flooding experiments were conducted under reservoir conditions using representative native cores, CO2, and synthetic formation brine. Abrupt changes in differential pressure (ΔP), analysis of effluent collected after CO2 multi-rate flow, and pH reading are the key indicators to consider that the condition has reached a critical rate. The experimental result demonstrated the existence of fines migration, scale formation, and salt precipitation after the core was subjected to supercritical CO2 multi-rate flow. Considering these issues and challenges associated with injectivity, this study recommended a maximum injection rate prior to field scale injection

Multiple stages of continental rifting in Eastern Peninsular Malaysia: New insights from Jurassic–Cretaceous granitoids

Supplementary Table S2 Zircon in-situ Hf isotopic data for the Middle Jurassic–Early Cretaceous granitoids in East Malaya

Multiple stages of continental rifting in Eastern Peninsular Malaysia: New insights from Jurassic–Cretaceous granitoids

Supplementary Table S1 LA–ICP–MS zircon U–Pb age data for the Middle Jurassic–Early Cretaceous granitoids in East Malaya

Mineralogy and Geochemistry of the Paleocene–Eocene Palana Formation in Western Rajasthan, India: Insights for Sedimentary Paleoenvironmental Conditions and Volcanic Activity

Organic-rich shale rocks from the Paleocene–Eocene Palana Formation in western Rajasthan, India, were systematically investigated based on inorganic and organic geochemistry combined with microscopic examinations to evaluate the sedimentary paleoenvironmental conditions and volcanic activity and their impact on the high organic carbon accumulation. The Palana shales are categorized by high organic matter (OM) and sulfur contents, with total values up to 36.23 wt.% and 2.24 wt.%, respectively. The richness of phytoplankton algae (i.e., telalginite and lamalginite) together with redox-sensitive trace elements further suggests a marine setting and anoxic environmental conditions during the Paleocene–Eocene. The significant low oxygen conditions may contribute to enhancing the preservation of organic matter during deposition. The mineralogical and inorganic geochemical indicators demonstrate that the Palana organic-rich shale facies was accumulated in a warm and humid climate with moderate salinity stratification conditions in the water columns, thereby contributing to the high bioproductivity of the phytoplankton algae blooms within the photic zone. The presence of significant contents of zeolite derived from volcanic material together with silica minerals such as apophyllite and tridymite in most of the Palana organic-rich shales indicates a volcanic origin and supports hydrothermal activities during the Paleocene–Eocene period. These volcanic activities in this case are considered the influx of large masses of nutrients into the photic zone due to the ash accumulation, as indicated by the presence of the zeolites in the Palana shales. Therefore, the high bio-productivity associated with effective OM preservation led to the organic carbon accumulation in the Palana Formation during the Paleocene–Eocene