Quantification of microporosity and its effect on permeability and acoustic velocity in Miocene carbonates, Central Luconia, offshore Sarawak, Malaysia

Carbonate reservoirs are mostly considered to be complicated since in the petroleum industry, and because predicting the quality and achieving a high recovery factor from these rocks is challenging. Carbonate rocks have a complex porosity, which often leads to substantial uncertainty in prediction of permeability values for any particular porosity figure. The petrophysical analysis of carbonate reservoirs is and prone to more significant uncertainty. Pore size in carbonates rocks varies from micro to cave system scale. Carbonates with moldic and vuggy porosity usually contribute positively to the hydrocarbon production, yet sometimes these pores are mostly unconnected, thus yielding low flow rates, even though micropores form a high component of the total porosity of a reservoir. This study explores the reservoir properties of carbonate rocks of Central Luconia (Offshore Sarawak, eastern Malaysia), with emphasis on the relevance of microporosity on permeability and acoustic velocity relationships. A petrographic study of 260 samples obtained from the reservoir interval of Well A in the Central Luconia, Malaysia, was conducted to identify pore types (moldic, vuggy, interparticle, intraparticle and fractures) and measure porosity (ranging from 4 to 25%). For microporosity quantification, an enhanced workflow is introduced using the Digital Image Analysis (DIA) technique, where 32 petrographic images of each thin sections were taken under the transmitted light microscope that covers the entire thin section. The DIA technique was then implemented on these petrographic images to quantify the amount of macroporosity. After that, the microporosity was calculated in the following way: the difference in value between the observed macroporosity using DIA, and the total porosity measured on core plugs. Finally, the resulting amount of microporosity was then correlated with acoustic velocity and permeability to determine if significant improvement is achieved in the coefficient of determination (R2). Moreover, it has increased from 0.55 to 0.67 for the permeability and from 0.61 to 0.87 for the acoustic velocity. The analysis also highlights that those samples with more substantial pores and a high figure (>50% of total porosity) of microporosity exhibit slower acoustic velocity for both P and S waves. Also, this study proposed a simple predictive model of elastic properties in the Central Luconian Miocene carbonate, Malaysia. © 2018 Elsevier B.V

AUGMENTED WIRELINE BASED LITHOLOGY AND FACIES PREDICTION, FOR UPPER ORDOVICIAN SUCCESSION, MURZUQ BASIN, LIBYA

The upper Ordovician reservoir is one of the leading producing units in SW part of the Murzuq basin; it has a complex architecture inherited from the glacial effects on the braided fluvial deposits of the late stage at this era. The ultimate target for any petrophysical evaluation is to determine the quantities of water saturation and porosity accurately, but unfortunately, the models for thinly interbedded sand and shale layers are not straightforward. Therefore in this paper, an effort has been made to delineate and distinct between the types of interbedded (shaly-sand and sandy-shale layers), and lithology end members by application compressional compliance versus density cross-plot in the two studied wells. After that, the determination of the thinly interbedded of layers type is augmented by correlating Vp-compliance with Poisson's ratio, effec tive porosity, and VP/VS. Among all the examined cross-plot; Poison's ratio, VP/VS and effective porosity with compressional compliance enhanced the upper and lower boundaries of the thinly interbedded sand and shale layers of the Ordovician succession in Murzuq basin. The Mamuniyat formation (main reservoir) with more clean sand content displays low compressional compliance, low-velocity ratio, and low Poisson's ratio. In contrary, the rich TOC shale (Hot shale) shows high compressional compliance, high-velocity ratio and high Poisson's ratio. While the disputed sandstone, siltstones and silty shales of late Ordovician Bir Tlacsin formation has slightly higher compressional compliance, velocity ratio, and Poisson's ratio than the underlying Mamuniyat formation, which enables drawing a clear contact between two gradually graded formations in the areas with no abrupt changes. The estimated petrophysical and elastic and properties are then used as an input for electrofacies prediction in both wells, by using unsupervised neural network classification. The predicted petrophysical facies clusters in both wells failed to differentiate between the various type of shales. However, the petro-elastic facies cluster reliably delineated the interbedded sandy- shale and shaly-sand thin layers without using gamma-ray logs. The results will help to avoid and to reduce the errors made during fluid substitution and rock physics models of shaly-sand formations. © 2018. All Rights Reserved

Antimicrobial activity of 7,3ʹ,4ʹ-trihydroxyflavonol isolated from Acacia nilotica var. ad stringens

Acacia species (Mimosaceae) is widely distributed in tropical and subtropical countries and has a variety of ethnomedicinal uses. There is inadequate laboratory investigation to identify bioactive compounds and therapeutic effect of Acacia nilotica var. ad stringens. This research has been conducted to extract, isolate and identify major compounds from heartwood of Acacia nilotica var. ad stringens and to test them against representative bacteria. Powdered air-dried heartwood of A. nilotica var. ad stringens has been extracted with methanol/water, 4:1 and the extract has been then purified using chromatographic techniques (column and paper chromatography). A pure flavonoid compound has been isolated and the structure has been elucidated based on extensive spectroscopic analysis procedures (IR, UV, 1H NMR, and mass spectrometery). The isolated compound has then been evaluated for antimicrobial potential against Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Bacillus subtilis, Bacillus cereus, and Staphylococcus aureus) using cup-plate agar diffusion method. The spectroscopic analysis of the isolated compound has led to its identification as 7,3ʹ,4ʹ-trihydroxyflavonol. The compound shows varying antimicrobial responses with high potency against Gram-negative human pathogens. The Gram-positive bacteria which are inhibited are Bacillus cereus, Corynebacterium sp., Enterococcus faecalis, Staphylococcus aureus , and Streptococcus agalactiae. The Gram-negative bacteria are Acinetobacterbaumannii , Acinetobacter sp. , Escherichia coli, Pseudomonas aeruginosa and yeasts are Candida albicans and Cryptococcus neoformans. The present study has demonstrated that 7,3ʹ,4ʹ-trihydroxyflavonol is an effective antimicrobial compound. If applied in suitable pharmaceutical formulations it could be valuable for treating various bacterial infections or introduced as adjunct treatment along with standard agents.

New approach towards the classification of microporosity in Miocene carbonate rocks, Central Luconia, offshore Sarawak, Malaysia

Microporosity is recognized as a significant concern in limestone reservoirs throughout the world because it presence can highly complicate the hydrocarbon estimation and production. Numerous studies around the globe emphasises on the physical appearance, occurrence, and abundance of microporosity, but no published study has been emphasises on the presence of microporosity in Miocene carbonate reservoirs. Miocene carbonates from Central Luconia, offshore Sarawak, Malaysia, contains a significant amount of micropores, which occurs in grain, matrix, and cement. For a better understanding of the presence of micropores, it is necessary to consider grains, matrix, cement, and pore types. Based on the qualitative and quantitative knowledge of these components a classification of micropores is proposed and their effect on reservoir quality. These results can reduce the number of the assumption made about the internal rock connectivity and quality.For quantitative analysis, 32 high-resolution images of each thin sections were taken under the transmitted light microscopy. Succeeding these 32 images were stacked together as a photo panel to enable quantifying the amount of grain, matrix, cement, pore types and macroporosity using Digital Image Analysis and J.Microvision software. Furthermore, Field Emission Scanning Electron Microscopy images were also used for the measurement of crystallometry of micrite particles, classification of micrite particles and the micropores.Eight facies scheme is introduced based on the detailed lithofacies study of five wells. The qualitative observation of thin sections unveiled that corals, red algae, green algae, foraminifera, echinoderms, sponge, bivalve, and bryozoans are the most dominant components. Foraminifera, red algae, and corals are the far most dominant components covering almost 50% of the total intervals. Regarding porosity types, the mouldic porosity is the far most dominant pore types with converting the total 50% of the interval. Lithofacies observed in these wells indicate a good reservoir quality, but diagenesis plays a vital role in enhancing or reducing their porosity and permeability. Most of the depositional textures of the reservoir are leached, making this location unique to study facies distribution and diagenetic history.Result exhibits that the micrite particles are classified into five classes, which are very fine, fine, medium, coarse and very coarse, with a diameter of 0.1–2 μm, 2–4 μm, 4–6 μm, 6–8 μm and 8–10 μm respectively. The texture and morphology of micrite microtexture are classified into six classes. Among these six classes, rounded, subrounded, trigonal, rhombic (micro-sub)-polyhedral micrite are representing porous micrite particles, whereas fitted bounded subhedral, and fitted fused anhedral are interpreted as tight micrite particles. Furthermore, five micropores classes are introduced based on the size of these particles. The empirical porosity-permeability relationship is affected by the presence of microporosity and its influences the assessment of ultimate recovery of hydrocarbons in Central Luconia, offshore Sarawak, Malaysia. Keywords: Quantification, Grain types, Porosity, Microporosity, Micrite particles, Central Luconi

Quantitative Interpretation of carbonate reservoir rock using wireline logs: a case study from Central Luconia, offshore Sarawak, Malaysia

The current study focuses on the quantitative evaluation of petrophysical parameters of selected wells using wireline log data in Central Luconia, offshore Sarawak. Based on the relatively high resistivity and, low-neutron/-density log responses, three major zones are identified. These include gas-bearing zones (Zone-1 and Zone-3) and mixed zone (Zone-2). The gamma ray, neutron and density logs confirmed that Well A was composed of carbonate rocks ranging from limestone to dolomite. Zone-1 and Zone-3 consist of limestone, whereas Zone-2 contains dolomite. The average porosity of these zones (Zone-1, Zone-2 and Zone-3) are 15.7, 4.3 and 13.7%, whereas gas saturation is 83, 41 and 93%, respectively. The permeability values are 543 mD (Zone-1), 47.7 mD (Zone-2) and 601.5 mD (Zone-3). The water saturation value in Zone-2 is very high, up to 66% compared to Zone-1 and Zone-3 which are 17 and 7%, respectively. It is pertinent to mention that Zone-1 and Zone-3 contain movable gas (i.e., HC movability index is less than 0.7). Furthermore, bulk volume water values in three zones (0.012, 0.0083 and 0.009) indicate the presence of irreducible water. In contrast, pore-filled dolomite cement is mostly from Zone-2, indicating high water, low gas saturation, low porosity and less movability index values, which indicate the presence of high microporosity. Additionally, bulk volume water suggests that these micropores are saturated with irreducible water. High microporosity affects the wireline log response in Zone-2 and therefore provides misleading information

High Resistivity Reservoirs (Causes And Effects): Sahara Field, Murzuq Basin, Libya

High and low resistivity values is an alarming phenomenon that is usually associated with a very complicated reservoir history and worth looking into. Ordovician sandstone reservoirs are the primary oil producers in the Murzuq basin oil fields that is characterized with an average porosity of 14%, permeability range 410-10,760 md and clean quartz aranite composition. More than fifty wells were drilled in Sahara oil field, but only four of them were announced to have high resistivity values more than 100k ohm-m and ten others to be considered as low resistivity wells (below 50 ohm-m). Therefore, average deep resistivity was mapped in both water and oil legs using all available data set, and the top reservoir was employed as a trend map. They showed distinctive trends for low resistivity readings in oil-leg and confirmed the extreme deep resistivity nature for the wells (W7, W8, W9, and W10). Height above oil water contact and capillary pressure was also calculated for all the wells and revealed a high pressure (400 psi) at the location of the high resistivity wells. As a result, of higher capillary pressure in thicker reservoir area oil might have been able to displace water through geological time by benefitting of more considerable height above oil-water contact, higher connate pressure, and buoyancy forces support, which resulted in occupying all the larger pores and pushed the water into minor scattered pores leading to gradual alteration of reservoir wettability from water to oil-wet. Hence, the brine fluids will no longer be connected to each other inside the pore system. Therefore, they will lose their contribution to resistivity readings, and the resistivity tool will encounter a more resistant medium, which in turn will lead to underestimation of water saturation.</jats:p

Association between Vitamin D Status and Health Status of Adults in Western Libya

Vitamin D (VitD) is essential for health and preventing diseases. This study aimed to investigate the possible association between VitD status and health status in 306 Libyan male and female young adults (18–25 Y) and adults (26–65 Y). There were 89.54% of subjects that had VitD levels below normal (&lt;30 ng/mL), of which 45.42% were VitD deficient (&lt;10 ng/mL) and 44.12% were VitD insufficient (10–29.9 ng/mL). VitD deficiency was associated with higher fasting blood sugar (FBS), low-density lipoprotein (LDL), and triacylglycerol (TAG) levels. Young adults had lower VitD levels than adults, which was associated with some health conditions. VitD insufficiency was associated with higher body mass index (BMI) values in adults, especially females, with higher FBS levels in adult males and higher hemoglobin A1c (HbA1c) levels in adult females. VitD deficiency in young adults was associated with higher TAG levels (more likely in adults) and lower high-density lipoprotein (HDL) values. Furthermore, VitD deficient adult females appeared to have a higher risk of sleeping problems, psychological disorders, headache, and osteoporosis, whereas their male counterparts appeared to be at a higher risk of developing obesity and diabetes mellitus (DM). Findings showed a serious prevalence of VitD inadequacy in the Libyan population, which appears to negatively affect health status and be associated with some disease conditions.</jats:p