Eswaran Padmanabhan

Soil carbon stocks in Sarawak, Malaysia

The relationship between greenhouse gas emission and climate change has led to research to identify and manage the natural sources and sinks of the gases. CO2, CH4, and N2O have an anthropic source and of these CO2 is the least effective in trapping long wave radiation. Soil carbon sequestration can best be described as a process of removing carbon dioxide from the atmosphere and relocating into soils in a form that is not readily released back into the atmosphere. The purpose of this study is to estimate carbon stocks available under current conditions in Sarawak, Malaysia. SOC estimates are made for a standard depth of 100 cm unless the soil by definition is less than this depth, as in the case of lithic subgroups. Among the mineral soils, Inceptisols tend to generally have the highest carbon contents (about 25 kg m(-2) m(-1)), while Oxisols and Ultisols rate second (about 10-15 kg m(-2) m(-1)). The Oxisols store a good amount of carbon because of an appreciable time-frame to sequester carbon and possibly lower decomposition rates for the organic carbon that is found at 1m depths. Wet soils such as peatlands tend to store significant amounts of carbon. The highest values estimated for such soils are about 114 kg m(-2) m(-1). Such appreciable amounts can also be found in the Aquepts. In conclusion, it is pertinent to recognize that degradation of the carbon pool, just like desertification, is a real process and that this irreversible process must be addressed immediately. Therefore, appropriate soil management practices should be instituted to sequester large masses of soil carbon on an annual basis. This knowledge can be used effectively to formulate strategies to prevent forest fires and clearing: two processes that can quickly release sequestered carbon to the atmosphere in an almost irreversible manner.

Quartz surface morphology of Tertiary rocks from North East Sarawak, Malaysia: Implications for paleo-depositional environment and reservoir rock quality predictions

Abstract The relationship between quartz surface textural defects (derived from weathering and diagenesis), palaeo-depositional environment and reservoir quality were studied using Tertiary outcrop rock samples obtained from the Belait and Lambir formations of the Sarawak Basin, Malaysia. Thin sections were used for mineral identification and to make observations regarding grain size and texture. Morphological characterization of the samples was performed using scanning electron microscopy (SEM) attached with energy-dispersive X-ray spectrometry (EDX) system, to show variations in quartz surface texture. The SEM images of Belait conglomerates reveal euhedral quartz crystals characterized with prominent mechanical weathering defects (such as straight and conchoidal fractures and striations). Conversely, the analysis of the Lambir sandstones identified chemical weathering features (such as chemical etchings, pitting, solution pits and notches). On the basis of petrology, SEM and CT scan images, evaluation results of reservoir quality indicate that the Lambir Formation in this study area is high-energy coast deposit, with apparent tide-dominated features; while Belait Formation is neritic-delta deposit, with obvious wave-dominated features; reservoir quality of the Belait Formation and Lambir Formation are poor, but the porosity of the Belait Formation is relatively higher than that of the Lambir Formation.

Geochemistry of Miocene sedimentary rocks from offshore West Baram Delta, Sarawak Basin, Malaysia, South China Sea: implications for weathering, provenance, tectonic setting, paleoclimate and paleoenvironment of deposition

Geochemistry, paleoweathering, provenance, tectonic setting, paleoclimate and paleoenvironment of deposition of offshore Miocene sedimentary rocks in the West Baram Delta have been examined through multi-element geochemistry and mineralogy. Materials and methods used in the study include ninety four core samples from four subsurface wells, XRF, thin sections and FESEM. Four main groups of samples are identified in the wells: porous sandstones, cemented sandstones, siltstones and mudstones. The sandstones are classified as sublitharenites, litharenites and Fe-rich sandstones based on chemical composition and mineralogy. Variations in compositional trends suggest strong lithological and diagenetic controls on the geochemical composition of the samples. Petrography of the samples indicates that they are composed mainly of quartz, K-feldspar, siderite and clay minerals. The samples are characterized by moderate to high degree of chemical weathering with CIA values between 52–76 and PIA values from 65–100. Provenance analysis of the samples shows predominantly felsic and intermediate igneous provenance with minor mafic contribution. The samples are inferred to have originated from a passive margin tectonic setting that followed the continental collision and rifting stages of the foreland basin development phase of the Sarawak Basin. The paleoclimate of deposition of the samples is interpreted to be warm and humid enhancing the chemical weathering. The paleoenvironment of deposition is predominantly suboxic to anoxic.

Incorporation of silica into the goethite structure: a microscopic and spectroscopic study

Quartz and iron (hydr)oxide are reactive surface phases that are often associated with one another in soils and sediments. Despite the several studies on the coating of quartz with iron oxides, the reactivity of dissolved species (Si) leached from quartz with iron (hydr)oxides has received limited attention. In this study, goethite synthesized on quartz substrates were characterized using field emission scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy, and Fourier-transform infrared (FT-IR) spectroscopy. The SEM characterization revealed that bundles of thin parallel aligned goethite rods were formed at pH > 10, while large pseudohexagonal crystals of twinned goethite needles were synthesized at pH ≤ 10 after dehydration and hydration in the alkaline media. TEM analysis showed expanded and distorted lattice spacing of the crystal structure of iron (hydr)oxide due to silica incorporation. The characterization showed that silica increased the crystallite size of the goethite and transformed its acicular texture to a larger, twinned needle structure. FT-IR and XRD analyses revealed band shifts in crystal bonds as well as new bond formations, which indicate the presence of changes in the chemical environment of Fe–O and Si–O bonds. Thus, the presence of sorbed silicates modifies the crystal and lattice structure of goethite.

Hydrocarbon Bond Variation in Some Shales from Batu Gajah, Malaysia

This study demonstrates the variation in aliphatic hydrocarbons in shales by Fourier transform infrared (FTIR) spectroscopic characterization from an isolated outcrop of Batu Gajah area, Malaysia. IR spectra of analyzed sample indicate alkanes, alkenes and alkynes groups of aliphatic hydrocarbon. The spectra indicated the variation in the distribution of the aliphatic hydrocarbon groups. =C–H bonds occur as dominant peaks in the spectra. The main peaks in the infrared spectra reflected alkane methyl symmetric C–H stretching, Alkyne C=C stretching, alkene =C–H stretching bonds. Alkyne and alkene aliphatic hydrocarbons have higher peak intensities in samples B1 and B8, respectively. The Presence and absence of alkene aliphatic hydrocarbon in samples of units 2 and 3 also have been observed. Total organic carbon content also has been measured for ten samples. All sample had a variation in TOC values, while B1 sample of unit 1 had an exceptional (3.501%) value of TOC.

An enhanced approach to predict permeability in reservoir sandstones using artificial neural networks (ANN)

A key challenge in the oil and gas industry is the ability to predict key petrophysical properties such as porosity and permeability. The predictability of such properties is often complicated by the complex nature of geologic materials. This study is aimed at developing models that can estimate permeability in different reservoir sandstone facies types. This has been achieved by integrating geological characterization, regression models and artificial neural network models with porosity as the input data and permeability as the output. The models have been developed, validated and tested using samples from three wells and their predictive accuracy tested by using them to predict the permeability in a fourth well which was excluded from the model development. The results indicate that developing the models on a facies basis provides a better predictive capability and simpler models compared to developing a single model for all the facies combined. The model for the combined facies predicted permeability with a correlation coefficient of 0.41 which is significantly lower than the correlation coefficient of 0.97, 0.93, 0.99, 0.96, 0.96 and 0.85 for the massive coarse-grained sandstones, massive fine-grained sandstones-moderately sorted, massive fine-grained sandstones-poorly sorted, massive very fine-grained sandstones, parallel-laminated sandstones and bioturbated sandstones, respectively. The models proposed in this paper can predict permeability at up to 99% accuracy. The lower correlation coefficient of the bioturbated sandstone facies compared to other facies is attributed to the complex and variable nature of bioturbation activities which controls the petrophysical properties of highly bioturbated rocks.

Enhancing the Interpretation of Rift Structures in Sudan Using AVO Analysis and Seismic Inversion

Uncertainty in structural complexities and rock heterogeneities is a major challenge that controls oil exploration and drilling operations in the rift basins of Sudan.

Perturbation of Homogeneous Thermal Conductivity Distribution in Some Carbonates by Stylolites

Stylolites are partings within rocks that exhibit complex mutual column and socket interdigitization. These features can exhibit pronounced roughness on several scales. Stylolites, under deep-burial conditions, could permit circulation of undersaturated fluids and become reservoirs allowing also deep commercial gas production. However, the impact of stylolites on variations in thermal conductivity in carbonates is not well-known. This study was undertaken to investigate the heterogeneity in thermal conductivity in a variety of carbonate specimens containing different types of stylolites.

Impact of Shifting Agriculture on the Sustainability of Anthroscapes in Sarawak, Malaysia

Shifting cultivation has a negative connotation particularly in western societies. It is viewed as a system that progressively deforests without attempts to regenerate the forests. Although the system is practiced in many developing countries its contributions to the forest ecosystem and the low-input agricultural system is not recognized. A major advantage is the biodiversity that prevails in this system in comparison to that which exists in the mono-clonal plantations. Mismanaged systems can lead to a land becoming a biodiversity-desert. Shifting cultivation, as practiced by the forest communities is a viable, sustainable enterprise but becomes compromised by modern interventions. Despite the negative connotations, the impact of shifting cultivation can be contained in a sustainable land management system. Precise data on spatial distribution of land areas affected by shifting cultivation is needed. The degradation potential of various fragile systems where shifting agriculture has been detected, can be ascertained with greater precision with such precise data.