Logging Techniques Research Articles

Investigating the writing performance of educationally at-risk examinees using technology

This article demonstrates how recent advances in technology allow fine-grained analyses of candidate-produced essays, thus providing a deeper insight on writing performance. We examined how essay features, automatically extracted using natural language processing and keystroke logging techniques, can predict various performance measures using data from a large-scale and high-stakes assessment for awarding high-school equivalency diploma. The features that are the most predictive of writing proficiency and broader academic success were identified and interpreted. The suggested methodology promises to be practically useful because it has the potential to point to specific writing skills that are important for improving essay writing and academic performance for educationally at-risk adult populations like the one considered in this article.

Analysis Of the Behavior of Cyberattacks on Online Services Using the Cyber Threat Classification

The paper contains a study of the dynamics of attacks on online services using the categorization of cyber threats by type in the corporate network of the Krasnoyarsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences. The study was conducted using online service logs and allows solving pressing issues related to ensuring the built-in security of web services, such as: identifying both current and future cybersecurity risks. A summary of the most important logging and analysis techniques is provided. The authors describe the nature and content of the data sources and the software used. The extensive observation period of the study is one of its outstanding features. The structure of the processing system is provided and software tools for attack analysis and categorization are created. The paper shows that using categorized sampling allows for the detection of periodicity and the identification of patterns in specific types of attacks. A correlation matrix was created based on the type of attack. Except for Command Injection, Directory Browsing, and Java Code Injection attacks, which can be aggregated, the research found that most attack types had poor correlation. Based on the classification of cyber threats, the authors proposed a heuristic technique of risk comparison.

An integrated sedimentological, rock typing, image logs, and artificial neural networks analysis for reservoir quality assessment of the heterogeneous fluvial-deltaic Messinian Abu Madi reservoirs, Salma field, onshore East Nile Delta, Egypt

This study introduces an integrated evaluation of geological and geophysical data, including sedimentology, diagenetic alteration, image log analysis, core measurements, formation evaluation, and a neural analysis technique (K-mode algorithm) to characterize the upper Messinian heterogeneous reservoirs of the Salma Field, Nile Delta, Egypt. It links observed reservoir permeability and flow zone indicators (FZI) to predict reservoir quality and distribution within un-cored parts of the field. Core and image log analysis show that the Abu Madi sandstone reservoir is composed of seven clastic litho-facies deposited within fluvial to deltaic environments. The reservoir is controlled by four hydraulic flow units (HFU's) and five flow units (FU). Fluvial channel facies, tidally influenced fluvial channel facies, and uppermost parts of bayhead delta facies are dominated by clean sandstone with a low clay content (avg. 20%). These facies are characterized by the high pore-throat sizes (R35 and FZI values), indicating a pore system dominated by mega-to macro-pores. The estuarine facies is composed of mudstone, siltstone, and argillaceous sandstone, with 25% average clay content and moderate R35 and FZI values, indicating a pore system dominated by macro-to meso-pores. The heterolithic estuarine and bayhead delta facies contain abundant argillaceous-rich sandstones, with 29% average clay content and low R35 and FZI values, indicating a pore system dominated by micro-pores. A neural log technique was applied to predict FZIs and permeability in un-cored intervals. Paleocurrent analysis was conducted using image log data to guide sweet spot and reservoir quality tracking across the field. Reservoir quality is controlled by both diagenetic and depositional processes, chiefly an abundance of detrital clays, grain size, and sorting. In the Salama Field reservoirs, mineral dissolution, cement dissolution, and micro-fractures enhance the pore system, while pore-filling and grain-coating detrital clays reduce reservoir quality. These results are important as they improve the wider understanding of the Messinian Abu Madi reservoir in the wider Mediterranean region.

New geophysical logging techniques for practical problem solving at complex hydrogenetic uranium deposits

In-situ uranium recovery features high economic efficiency and low environmental impact as compared with other uranium production techniques. The article presents the experimental results on the application of new geophysical logging methods at a uranium deposit of hydrogenetic type. Complex hydrogenetic uranium deposits have a nonuniform lithology, varied permeability and alternation of permeable and water-resistant rocks. The development of such deposits is often complicated by a number of factors affecting the production process. The common methods of geophysical research in wells provide insufficiently reliable information about the geological structure of interwell space. As a result, it is difficult to control and monitor the production process, which can lead to inefficient consumption of chemical reagents, undesirable leakage beyond the limits of production blocks, incomplete extraction of uranium reserves, etc. To solve the problem of insufficient studies of interwell space, the method of radiowave geointroscopy was tested. This method is based on the measurement of electrical resistance. The tests were carried out in two stages, during the periods of high-rate production. By comparing the measurement results in different dimensions, the electrical resistance maps were plotted. The interpretation of the measurement results made it possible to obtain reliable data on the actual distribution of solutions in the interwell space in a given period of time, to identify areas of excessive concentrations of solutions (stagnant zones), to assess acidification dynamics in production blocks, and to delineate potentially difficult areas of the blocks.

Quaternary environmental and climatic history of the northern high latitudes – recent contributions and perspectives from lake sediment records

ABSTRACTLake sediment records archive the Quaternary environmental and climatic history in northern high latitudes. Because of their spatial distribution, age range, time resolution, age control, and high sensitivity to paleoenvironmental conditions, lake records contribute to evaluating regional to hemispheric‐scale climate change. Here, we compare the characteristics of lake sediments and their qualities for paleoenvironmental and paleoclimatic reconstructions with those of other archives in northern high latitudes, and we outline the current state of research by introducing a series of regional case studies on 31 lakes as part of this special issue. The compilation shows that the coring site selection and interpretation can strongly benefit from bathymetric and seismic or hydro‐acoustic surveys. New coring techniques have become available making it possible to expand the records in length and time. Analytical work on the cores has particularly benefited from improved non‐destructive logging and scanning techniques, from the development of new proxies, and from advancements in quantitative climate reconstructions. Progress was also made in further developments of dating techniques; however, the recognition of additional isochronal events, e.g., via tephrochronology or paleomagnetic event stratigraphy, is needed to derive a better understanding of leads and lags in climate signal propagation throughout the northern high latitudes.

The symplectic isotopy problem for rational cuspidal curves

We define a suitably tame class of singular symplectic curves in 4-manifolds, namely those whose singularities are modeled on complex curve singularities. We study the corresponding symplectic isotopy problem, with a focus on rational curves with irreducible singularities (rational cuspidal curves) in the complex projective plane. We prove that every such curve is isotopic to a complex curve in degrees up to five, and for curves with one singularity whose link is a torus knot. Classification results of symplectic isotopy classes rely on pseudo-holomorphic curves together with a symplectic version of birational geometry of log pairs and techniques from four-dimensional topology.

Diagenesis and reservoir quality of Oligocene Barail Group of Upper Assam Shelf, Assam and Assam Arakan basin, India

The Oligocene Barail deltaic sandstones are the main oil reservoirs in Upper Assam Basin. Nonetheless, the diagenetic alterations and their impact on reservoir quality on Barail sandstones are virtually unknown. The present study aims to know the ways diagenesis plays the role for the invariable hydrocarbon production from these clastic reservoirs within the Barail Group. Samples representing the lower unit of Barail Group known as Barail Main Sand (BMS) and the upper unit known as Barail Coal Shale (BCS) were studied using a combination of petrographic, scanning electron microscopy (SEM), X-ray diffraction (XRD) of clay and wireline log techniques. The average framework composition of BMS is Q49.42F4.18R14.75 while the BCS are composed of Q51.33 F3.89 R14.04. The BMS are moderately hard, fine to medium grained, sub angular to sub rounded, moderately well sorted, dominantly of lithic arenite type and porosity value ranges from 10 to 22.01%. The sandstones of BCS Unit are moderately hard, light grey, fine to very fine grained and usually have low porosity except the channel sands. Both the BMS and BCS have undergone various diagenetic alterations which are observed as mechanical compaction, authigenesis of cements and clays, dissolution and alteration of unstable clastic grains. The identified clay minerals are kaolinite, illite and chlorite. Smectite is occasionally observed as mixed layered smectite-illite clay. The diagenetic alterations along with the clay minerals occupying as pore-filling and lining cements have critically influenced the reservoir quality of both BMS and BCS units of Barail Group. Proper treatment of these clay minerals could aid in the prevention of formation damage to a large extent.

Bulk Density Response and Experimental Study of Pulsed Neutron-Gamma Density Logging

The pulsed neutron-gamma density logging technique is used to measure the bulk density of formations based on the detection of gamma rays from the inelastic scattering of neutrons in the formations. However, the induced gamma ray source is regarded as a function of neutron transport and cannot be considered a “point” source. Due to the high energy level of gamma rays, the attenuation of inelastic gamma rays is affected by Compton scattering and pair production. Therefore, bulk density can be measured using inelastic gamma rays while considering the effects of neutron transport and pair production. In this article, a novel density measurement method that uses a completely different response model is proposed to improve the accuracy of density measurement. The process of neutron-gamma density measurement is divided into the neutron transport group and the gamma ray transport group in accordance with the neutron-gamma coupled field theory. A novel density estimation algorithm is derived from the diffusion equation and the gamma ray attenuation law. The accuracy and specification of density measurement are investigated through the Monte Carlo simulation and the calibration of test pits. Theoretical and experimental analyses show that the neutron transport and gamma ray transport are not entirely independent of each other in the pulsed neutron-gamma density measurement. The newly developed model can effectively enable the inelastic gamma rays to conform to the gamma ray attenuation law and keep the measurement accuracy at ±0.025 g/cm3. Moreover, neutron-gamma density is insensitive to the porosity and lithology of the formation. The proposed novel algorithm successfully establishes the calculation model for the relationship between inelastic gamma rays and bulk density, providing a new perspective for density measurement in pulsed neutron-gamma density logging.

Development of Site-Scale Conceptual Model Using Integrated Borehole Methods: Systematic Approach for Hydraulic and Geometric Evaluation

Understanding the physical flow mechanisms in aquifer systems is essential in effectively protecting groundwater resources and preserving subsurface environments from a wide range of contaminants. A conceptual model is a simplified representation of a groundwater system and gaining knowledge about the geological features and parameters controlling the flow and transport processes is a crucial first step towards properly constructing a site-scale conceptual model. In this study, we present a multi-step workflow that involves integrated borehole techniques to gain information concerning groundwater flow. Measurements from core-scale to field-scale enable us to better build a subsurface geological structure divided into the unconsolidated layer and the fractured bedrock. In addition, neutron logging and mercury injection capillary pressure techniques allow for the development of vertical porosity distribution in the alluvial layer. For fracture characterization, the fracture geometry is delineated using a series of borehole imaging techniques and single-hole tests to differentiate the individual permeable fractures from other hydraulically inactive fractures. Combining the hydraulic and geometric evaluations, the presence of large-scale connective fracture networks is identified. Our high-resolution three-dimensional (3D) site-scale conceptual model is expected to contribute to improving the reliability and availability of numerical groundwater models.

Automated porosity estimation using CT-scans of extracted core data

Estimation of porosity at a millimeter scale would be an order of magnitude finer resolution than traditional logging techniques. This enables proper description of reservoirs with thin layers and fine scale heterogeneities. To achieve this, we propose an end-to-end convolutional neural network (CNN) regression model that automatically predicts continuous porosity at a millimeter scale resolution using two-dimensional whole core CT scan images. More specifically, a CNN regression model is trained to learn from routine core analysis (RCA) porosity measurements. To characterize the performance of such approach, we compare the performance of this model with two linear regression models trained to learn the relationship between the average attenuation and standard deviation of the same two-dimensional images and RCA porosity. Our investigations reveal that the linear models are outperformed by the CNN, indicating the capability of the CNN model in extracting textures that are important for porosity estimations. We compare the predicted porosity results against the total porosity logs calculated from the density log. The obtained results show that the predicted porosity values using the proposed CNN method are well correlated with the core plug measurements and the porosity log. More importantly, the proposed approach can provide accurate millimeter scale porosity estimations, while the total porosity log is averaged over an interval and thus do not show such fine scale variations. Thus, the proposed method can be employed to calibrate the porosity logs, thereby reducing the uncertainties associated with indirect calculations of the porosity from such logs.

Applications of well logging techniques to evaluate the groundwater aquifers in the area between southwest Bani Sweif and west Asyoute governorate, upper Egypt.

The relevance of detecting aquifer characterization and aquifer potential has risen with the application of well logging techniques as the demand for water has increased. Apart from pumping data, 16 geophysical well logs (resistivity, gamma ray, self-potential, and nuclear logs) are utilized to achieve the main goal of estimating petrophysical parameters (porosity (∅), effective porosity (∅𝑒𝑓𝑓), hydraulic conductivity (k), permeability (K) and shale volume (𝑉𝑠ℎ)) of the Apollonia (Eocene fractured limestone aquifer), Upper and Lower Bahariya (Nubian sandstone aquifer) formations. The findings show that the Eocene fractured limestone aquifer has a carbonate in soft chalk with high K and ∅ as well as high k of 4974.39 mD at well ST-188 (a highly productive aquifer), whereas the Lower Bahariya formation is mostly fine to medium-grained sandstone and clay, suggesting that it formed in shallow marine environments with low K. On the other hand, Upper Bahariya was noted that having poor sand succession. As results shown, K of the most examined wells ranges from 2609.69 to 1486.812 mD at ST-258 and ST-38 wells respectively. The study appears that 𝑉𝑠ℎ, along with ∅ and K features, is regarded as an important attribute in aquifer evaluation where, estimated 𝑉𝑠ℎ over the studied area is ranges between 5.96% and 31.7% at ST-48 and WBS1 wells respectively. Overall, this study provides an important insight into the importance of evaluating groundwater aquifers over time to help in making decisions to save and protect groundwater aquifers in the future.

Assessment of Environmental Pollution using Electrical Resistivity and Logging Techniques over A Municipal Dumpsite of Ijagun Ijebu Ode

The present study aims to assess environmental pollution using the resistivity method and geological logging technique over a municipal dumpsite of Ijagun Ijebu Ode, underlain by the Afowo Formation within the Dahomey Basin southwestern Nigeria. Forty vertical electrical resistivity soundings stations and six 2D electrical resistivity imaging profiles using Schlumberger and Wenner array respectively with maximum spread-length of 40m at each sounding and profile length of 60 m and 120 m and one borehole log were carried out. Three geoelectrical layers were obtained in the control area, their resistivity values with their corresponding depth of sediment materials is 126 Ωm – 724 Ωm at depth range 0.9 m – 1.1 m (topsoil), 608 Ωm – 2517 Ωm at depth range 3.5 m – 17.7 m (sandy layer), and 800 Ωm – 6046 Ωm (dry sandy layer). Along with the 2D resistivity imaging profiles over the control (1 and 2), four geo-electric layers characterized by Resistivity values range of 40 Ωm – 126 Ωm (loam), 135 Ωm – 418 Ωm (loamy sand), 500 Ωm – 1500 Ωm (sandy), and >3000 Ωm (dry sand) were revealed. The lithology recovery from the logging techniques shows the subsurface is underlined chiefly with sand, which shows a significant correlation with the geophysical method. The lower values of resistivity at the dumpsite are clear evidence of the subsurface contamination of the sandy layer. The 2D images revealed the contaminated zone thickness ranges from 2 m in the northwest to 25 m in the southeastern part. The protective capacity map derived from the VES showed that the dumpsite is underlain by poorly protected sandy lithology, prone to leachate infiltration. Relocation of the dumpsite to a better protected environment or underlining the present area with an impermeable geotextile layer would halt further leachate invasion into the subsurface.

Novel Proppant Logging Technique for Infill Drilling of Unconventional Shale Wells

Summary During the development of an unconventional play, wells are drilled and completed in batches, and depending on the development plans, current and expected energy market trends, as well as other developmental considerations, new wells are drilled and hydraulically fractured later near existing producing laterals. This creates challenges in terms of optimizing resource recovery and reducing interwell communication. A novel approach is proposed that utilizes systematic composite sampling and analysis of drilling mud returns to look for and quantitatively identify sand particles. The workflow involves cleaning, drying, and segregation of samples into sizes of interest to us (size distribution of pumped proppant in offset parent wells). These samples are imaged at a very high resolution and analyzed for grains using characteristic optical imaging properties to classify proppant sand particles using computer vision algorithms. Further analysis, such as elemental compositional analysis, is used to validate the results from the imaging workflow. We present a case study from the Permian Basin, where a new child well was used as a test case to prove this technology at the Hydraulic Fracturing Test Site (HFTS-2) in Delaware Basin. We introduce new proppant parameters that help identify sustained proppant zones vs. localized propped fractures. We have used additional diagnostics and data collected at the test site to validate observations from the proppant log and have successfully interpreted significantly propped vs. unpropped zones. A key finding from this test has been the significant proppant transport distances observed away from parent wells. Observable proppant was found at a lateral distance of approximately 425 m for one set of parent wells and more than 915 m for another set of parent wells. While a major limitation of this technique is the sampling rate, given adequate sampling, the proposed technology represents a systematic and one-of-a-kind interpretation of spatial proppant distribution while drilling infill wells. It provides us with unique opportunities to better understand the current state of the reservoir being targeted, including zones that are likely highly drained relative to others, and how the planned hydraulic fracturing of child wells can be improved.

Assessing geodynamic activity of rock by the borehole survey results

Research objective is to assess the modern geodynamic environment of the geological environment through borehole measurements of signals of geoacoustic emission and electromagnetic radiation. Research relevance is due to the need to identify geodynamically active zones and areas of increased rock fracturing in wells. Methods of research. Rock geodynamic activity was studied in a well of the North-Taratashsky area of a magnetite quartzite deposit in the Chelyabinsk region. MESh-42 hardware and software complex designed for synchronous registration of geoacoustic emission and electromagnetic radiation signals was used to solve this problem. Geoacoustic emission (GAE) and electromagnetic radiation (EMR) signals were recorded using the shuttle logging technique, which makes it possible to identify zones of rock geodynamic activity along well sections and track the dynamics of these sections in time. Results. The results of the method of geoacoustic emission and electromagnetic radiation signals shuttle logging in well no. 7 of the North-Taratashsky area are shown. Conclusions. In the course of geoacoustic emission and electromagnetic radiation signals studies in well no. 7 of the Severo-Taratashsky area according to the shuttle logging method, zones of increased stress in the geological environment and areas of increased fracture formation were identified, which, in turn, made it possible to subdivide the studied interval according to the geodynamic activity of rocks

Well integrity evaluation using acoustic and electromagnetic measurements

The evaluation of downhole well integrity is an important business for the oil and gas industry. It is driven primarily by the need to optimize production while maintaining a safe environment despite the inexorable corrosion of casing strings and other harsh downhole conditions. Furthermore, with aging infrastructure, evaluating well integrity to plan plug and abandonment or slot recovery projects is critically important. Many technologies have been developed to address the challenges of evaluating casing and cement integrity under varied downhole conditions. These technologies are necessarily growing increasingly more sophisticated to meet the requirements of evaluating multiple cemented casing strings. In particular, wireline cased-hole logging techniques based on electromagnetic (EM) and acoustic techniques have been applied to casing corrosion and cement integrity evaluation. The acoustic measurement techniques deployed for well integrity evaluation typically include the sonic frequency range of tens of kilohertz up to the ultrasonic frequency range of megahertz. The frequency ranges are appropriate for characteristic resolutions of decimeters down to millimeters for sonic and ultrasonic measurements, respectively. These techniques are sensitive to the elastic properties of materials in the well completion and crucial for assessing zonal isolation. In the domain of evaluating corrosion in one or multiple casing strings, the traditional measurement approach uses EM techniques, which are sensitive to the metal thickness, the electrical conductivity (the inverse of electrical resistivity), and the magnetic permeability of ferromagnetic pipes. The spectrum of common EM casing inspection techniques encompasses a frequency range between quasi-static (direct current) up to about 100 kHz. More recently, transient EM or pulsed-field eddy current tools have been introduced. Specific physics and challenges associated with well integrity measurements must be understood and considered in existing and emerging technology solutions.

A new method to predict brittleness index for shale gas reservoirs: Insights from well logging data

Brittleness is a significant mechanical property which determines the degree of fracturing difficulty in shale gas exploitation and hence, the brittleness index (BI) is a key parameter for the selection of suitable hydraulic fracturing intervals in shale gas reservoirs. However, at present there are no universal and convenient methods for the prediction of BI. Therefore, this study proposes a well logging data-driven BI prediction method based on principal component analysis (PCA) and back-propagation neural networks (BPNN), which can interpret nonlinear and complex relationships between predictors (input variables) and predicted values (target variables). Specifically, 63 samples and their corresponding well logging data were collected from the Wufeng-Longmaxi and Baota formations at the periphery of Sichuan Basin. Experimentally measured brittleness index (BIcore) values (from 0.18 to 0.88) derived from compression test stress-strain curves, were considered as the target parameter. Based on the results of linear regression and sensitivity analysis, five types of well logging, including gamma ray (GR), density (DEN), compressional wave slowness (DT), neutron porosity (CNL) and spontaneous potential (SP), were selected as appropriate well logging techniques. Three principal components were extracted from the five well logging datasets using PCA. Following PCA, the back-propagation neural network (PCA-BPNN) model exhibited excellent prediction accuracy according to statistical and graphical error analysis. The established PCA-BPNN model was then applied to forecast the BI profiles of the intervals of interest in well Y1 in the study area and the predicted BI values were found to be in agreement with the laboratory measured BIcore values. Therefore, the established PCA-BPNN BI prediction method can be applied to accurately locate suitable hydraulic fracturing intervals for economic and technical practicality.

Stackable Transactional File System Using Kernel-Level WAL

User applications that require transactional file access generally use user-level transactional protocols such as logging, atomic rename, since the POSIX interface does not support transactional file operations. The user-level protocols are complex and require specific persistence properties of file systems for correctness. If the kernel provides transactional access to file data, application developers can avoid the complex and error-prone application-level protocols. Many previous studies on kernel-level transactional support have several critical limitations such as complex APIs, file system-dependence, and low transaction concurrency. In this paper, we propose a kernel-level write-ahead logging (WAL) technique, called KWAL. KWAL maintains user-transparent WAL files and redirects transactional IOs to them. Since KWAL is implemented as a stackable file system, it can be mounted over any native file systems, without modifying them. To provide a higher transaction concurrency while guaranteeing isolation, KWAL supports byte-level write conflict detection and repeatable read isolation. We also utilize a block remap technique to resolve the duplicate write problem of WAL-based transaction scheme. To demonstrate the usefulness of KWAL, we implemented a simple key-value store using KWAL APIs, fixed the wrong transaction implementation of the Git application, and simplified the implementation of the storage engines of MySQL and SQLite.

Petrophysical experiment-based evaluation method for the saturation of gas hydrate

The seas around China contain abundant non-diagenetic gas hydrate deposits. The traditional logging and evaluation techniques based on conventional oil and gas no longer satisfy the evaluation requirements of offshore gas hydrate layers, and it remains difficult to calculate the hydrate saturation accurately, which seriously restricts the accurate evaluation of the resources. Petrophysical experiments are an important means to study gas hydrate. By simulating the hydrate formation conditions in sediments under natural conditions, the study of various petrophysical properties of gas hydrate is essential to the exploration and development of hydrates and the prediction of reservoir parameters. In this study, a tetrahydrofuran (THF) solution, montmorillonite, and natural sea sand were selected to simulate the growth of gas hydrate based on its characteristics in the study area, and in situ CT scanning experiments were carried out at different hydrate formation stages to determine the microscopic morphologies of gas hydrates within the pore space. In addition, the acoustic wave and resistivity of hydrates with different saturations were measured. Forward modeling of a differential effective medium (DEM) model was conducted for the hydrate reservoirs with different saturations, and the gas hydrate morphology was analyzed. Thereafter, the hydrate saturation predictions based on the petrophysical experiments were analyzed. The results of these analyses indicate that the microscopic morphology of hydrates in the study area is primarily pore-filling form. Based on the saturation estimations using the Archie's law, Wood equation, time-average equation and the DEM method, and under the constraint of the acoustic and electrical measurement results of the petrophysical experiments, an electric acoustic joint model was built by integrating the resistivity and acoustic waves. The estimation results indicate that the joint electro–acoustic model is the best method for calculating the saturation in the study area. • Design of experiments to simulate gas hydrate generation with THF, montmorillonite, and natural sea sand. • Multiple hydrate saturation prediction methods based on acoustic, electrical, and petrophysical models. • Determination of microscopic morphologies of gas hydrate. • A joint acoustic and resistivity hydrate saturation prediction model based on hydrate petrophysical experiments.

The use of distributed acoustic sensing (DAS) in monitoring the integrity of cement-casing system

The integrity of cement sheath and the interface bonds of the cement-casing-formation system is critical in the oil and gas wells' productive life and even after its abandonment. For many years, cement bond logs (CBL) tools, as one of the vital logging techniques, have been extensively employed in industry to monitor and evaluate cement-casing-formation bonds. Though these techniques provide a clear view of cement sheath integrity quality, some controversies surround their applications. First, it is challenging to deploy these logs in extremely harsh environments. Second, it is impossible to obtain real-time diagnostic values with CBL logs since they only provide a snapshot in time. Undoubtedly, real-time monitoring of cement sheath integrity is critical to operational safety in oil and gas wells. Distributed acoustic sensing (DAS) has emerged as a novel technology to provide the industry with an opportunity to improve safety during production and minimize operational costs. There are various aspects of well integrity in which DAS would provide invaluable information to support decision-making for well integrity management. In this paper, we firstly present a review of cement sheath integrity evaluation with conventional logs, then a comprehensive review of distributed acoustic sensing technology, including deployment methods, working principle, data processing/analysis techniques, and the current advancement in the use of DAS in wells' integrity monitoring. We find that specially packaged DAS sensors exhibit extreme sensitivity to events occurring downhole and thus provide a trove of valuable information. Once this data is acquired, it is processed and analyzed to highlight acoustic components related to a particular event signature enabling events classification. However, we have noted that there is still a long way to go in realizing the full potential of DAS in cement sheath integrity monitoring. Therefore, to fast-track the maturation of DAS application in oil and gas well integrity evaluation, there is a need to develop laboratory simulation tools and methods.

Assessment of reduced impact logging technique at different logging intensity

Despite increased recognition of the value provided by forests, the tropical forest potential continued to be seriously degraded, especially by overexploitation. In the field of harvesting, achieving sustainable forest management requires environmentally responsible logging, hence the growing interest in reduced impact logging (RIL) as an alternative strategy to promoting good forestry practices be expected can continue to fulfil the functions of forest ecosystems. The study was conducted in 100 ha of the first cutting cycle and 200 ha of the second cutting cycle of 22 years logged over the forest in Indonesia Borneo. The degraded level is measured based on disclosed area, while potential production of the residual stand is predicted by using growth increment data from a permanent sample plot. Harvest intensity influence significantly to residual stand condition with a positive correlation. Potential production of residual trees in the first logged-over forest after 35 years is almost recovered then can be achieved sustainable yield. It means that 22 years is not a sustainable cutting cycle. The disclosure area after the second logging was high of 66.89 to 69.36. Potential production of residual trees was very low and need 35.5 to 42.8 years to recover, however, the cutting cycle needs a longer time to achieve sustainable forest management as long as 57.3 to 63.2 years. Based on this study, regulation of reduced cutting cycle on logged-over forest after 20 years is not recommended to implement in natural forests.