Gamma-ray Logs Research Articles

Outcrop-to-subsurface correlation and sequence stratigraphy of a mixed carbonate–siliciclastic ramp using element geochemistry and well logging; Upper Cretaceous Kometan Formation, Zagros Foreland, NE Iraq

Surface analogues are suitable tools to link reservoir models to real facies but they require a robust outcrop-to-subsurface stratigraphic correlation. In this study, we correlate gamma-ray (GR), and porosity logs from nine wells drilled in the Cretaceous Kometan Formation, a prolific carbonate reservoir of northern Iraq, with geochemical logs from three sections representing surface analogues. The sections were sampled for microfacies, X-ray diffraction mineralogy, and element geochemistry using X-ray fluorescence spectrometry calibrated by ICP-MS data. Six microfacies composed of mudstones to packstones with planktonic, and benthic foraminifers were identified in outcrop, and interpreted as middle ramp, outer ramp, and basin deposits. The microfacies show increasing Al and K, and decreasing Ca concentration trends from the middle ramp to the basin settings. Their subsurface analogues are carbonates, marls and shales with benthic foraminifers, deposited in proximal, inner to middle ramp parts of the Kometan mixed carbonate–siliciclastic ramp system. The K + Al logs are correlated for 33 km, and the subsurface GR logs for over 100 km distance, but both reflect detrital admixture in biogenic carbonate. However, the outcrop- and subsurface log patterns show opposite vertical trends. The subsurface, inner ramp GR maxima in the middle Kometan, correlate with the outcrop K + Al minima jointly reflecting landwards and seawards shifts of the middle ramp carbonate factory during transgressions and regressions, respectively. The maxima and minima are interpreted as maximum regression (mrs) and maximum flooding surfaces (mfs) in the T–R sequence-stratigraphic model. Neutron-density and sonic logs indicate that the best reservoir quality is achieved in fractured pure carbonates, which are controlled by these T–R cycles. The results highlight the importance of elemental geochemistry in stratigraphic correlation of lithologically uniform sequences, and suggest that outcrop geochemistry can be correlated with well logs.

A multidisciplinary approach to facies evaluation at regional level using well log analysis, machine learning, and statistical methods

Geological facies evaluation is crucial for the exploration and development of hydrocarbon reservoirs. To achieve accurate predictions of litho-facies in wells, a multidisciplinary approach using well log analysis, machine learning, and statistical methods was proposed for the Lower Indus Basin. The study utilized five supervised machine learning techniques, including Random Forest (FR), Support Vector Machine (SVM), Artificial Neural Network (ANN), Extreme Gradient Boosting (XGB), and Multilayer Perceptron (MLP), to analyse gamma ray, resistivity, density, neutron porosity, acoustic, and photoelectric factor logs. The Concentration-Number (C-N) fractal model approach and log–log plots were also used to define geothermal features. In a study on machine learning models for classifying different rock types in the Sawan field of the Southern Indus Basin, it was discovered that sand (fine, medium and coarse) facies were most accurately classified (87–94%), followed by shale (70–85%) and siltstone facies (65–79%). The accuracy of the machine learning models was assessed using various statistical metrics, such as precision, recall, F1 score, and ROC curve. The study found that all five machine learning methods successfully predicted different litho-facies in the Lower Indus Basin. In particular, sand facies were most accurately classified, followed by shale and siltstone facies. The multilayer perceptron method performed the best overall. This multidisciplinary approach has the potential to save time and costs associated with traditional core analysis methods and enhance the efficiency of hydrocarbon exploration and development.

Serra Geral Group plumbing system and 3D geological framework in Morungava region, southern Paraná-Etendeka LIP (Brazil): Evidence from borehole, geochemical, and petrophysical data

The Morungava region (east of Porto Alegre-Rio Grande do Sul, Brazil), in the southern half of the Paraná-Etendeka Large Igneous Province (LIP), hosts Serra Geral Group subvolcanic intrusions (sill complex). These intrusions comprise various chemical compositions, including high-Mg rocks. So far, only a few examples of high-Mg rocks have been discovered in the Paraná-Etendeka LIP. Many investigations have been conducted in the Morungava region, yet several questions regarding the distribution, geometry, composition, and structural framework of the subvolcanic bodies in the subsurface remain unanswered. Therefore, we built a three-dimensional geological model of the Serra Geral Group sills and their associated stratigraphic framework in the Morungava region. This was achieved through the combined analysis of geological data (boreholes and geological maps), as well as petrophysical and chemical data, to improve the understanding of these subvolcanic bodies underground. The stratigraphic framework depicts the Precambrian basement topography, the distribution of the Paraná Basin units, and the Rio Grande do Sul Coastal Plain strata, which span the majority of the examined area. To categorize the Serra Geral Group rocks intersected by the boreholes, we established a validation and correlation technique using three separate data sources: laboratory geochemical data, portable X-ray fluorescence measurements, and gamma-ray logs. Using this technique, we classified the Serra Geral Group rocks in the Morungava region into three types (1, 2, 3), which share compositional similarities with Palmas, Vale do Sol, and Torres formations, respectively. Additionally, we identified a fourth type that could be compared to the Lomba Grande Complex, Silica Saturated Olivine Tholeiite-type dikes, and some high-Mg rocks from Namibia.

Thermal conductivity of sediments from well-logs and its application to determine heat flow density in the Pannonian Basin, Hungary

The thermal conductivity of rocks can be deduced from available data of exploration wells such as core samples, cuttings, lithological descriptions and geophysical well logs. We present a methodology for determining the thermal conductivity of the Neogene and Quaternary clastic sediments in the Pannonian Basin using geophysical well logs and thermal conductivity data measured in laboratory. The lithological composition consisting of shale, sand and water was identified and the volumetric fractions of these components were derived from wireline logging data that included natural gamma ray, resistivity, bulk density and neutron porosity logs. The bulk thermal conductivity was computed by applying an appropriate mixing law using the thermal conductivity values of the lithological components. The thermal conductivities of the lithological components were determined by the best fit of the calculated bulk thermal conductivity values to the laboratory data. Different mixing models are recommended to calculate thermal conductivity of shales and sandstones. The thermal conductivity of shales was calculated with the weighted harmonic mean of the constituents, where the volumetric fractions and the porosity were the weights. The thermal conductivity of sandstones can be equally well estimated by the weighted geometric mean and the three component lower Hashin-Shtrikman bound. The geometric mean was used in calculations due its simplicity. Shale to sand ratio was utilized to separate shaly and sandstone samples. Heat flow density determination was carried out using the Bullard-plot technique with thermal conductivities calculated by our method. Heat flow density calculated by our method is in the range of heat flow density values previously conducted but with substantially lower uncertainties. The significance of the method is that it allows the harmonization of the heat flow density in the countries lying in the Pannonian Basin, because the Neogene and Quaternary sedimentary cycle resulting in the filling of the basin was uniform throughout the basin.

The effect of depositional environment on sustaining a carbon storage site

One of the most difficult challenges facing planet earth is climate change caused by an increase in the concentration of greenhouse gases. Increased effort is being placed on delineating and characterizing suitable geologic formations that can house these gases. As part of this effort, we studied how the depositional environment would influence the storage of CO2 in the Illinois Basin. Lithofacies of the Mt. Simon Formation within the Illinois Basin were interpreted from the core data available for one of the four wells. The lithofacies interpreted from the core data were correlated with the motifs of the gamma-ray (GR) log in order to synchronize the information. Based on the lithofacies from the core and GR log, the depositional environment was defined. This was further used to establish a stratigraphic correlation across the four wells. Petrophysical analysis was carried out to evaluate the suitability of the rock properties in storing CO2. Structural features such as faults were interpreted on the 3D seismic data to evaluate the sealing capacity of the Mt. Simon Formation. A conceptual model of the depositional environment was developed and integrated with the rock properties using sequential Gaussian simulation. CO2 gas was injected and simulated in the Mt. Simon geologic model to evaluate how the flow would be impacted by the formation's depositional environment over time. Based on the lithofacies interpreted from the geologic core data and GR log, four depositional environments were interpreted — a braided river system, a fluvial deposit, a flood plain/shallow ephemeral environment, and eolian deposits. The structural framework revealed that the lower section of the Mt. Simon Formation is laterally extensive and structurally controlled. This allows CO2 gas to be evenly distributed throughout the formation.

Real-Time Gamma Ray Log Generation from Drilling Parameters of Offset Wells Using Physics-Informed Machine Learning

Summary By 2026, USD 5.05 billion will be spent per year on logging while drilling (LWD) according to the market report from Fortune Business Insights (2020). Logging tools and wireline tools are costly services for operators to pay for, and the companies providing the services also have a high cost of service delivery. They are, however, an essential service for drilling wells efficiently. The ability to computationally generate logs in real time using known relationships between the rock formations and drilling parameters, namely, rate of penetration (ROP), rotations per minute (RPM), surface weight on bit (SWOB), surface torque (TQX), standpipe pressure (SPPA), and hookload (HKLD), provides an alternative method to generate formation evaluation information (analysis of the subsurface formation characteristics such as lithology, porosity, permeability, and saturation). This paper describes an approach to creating a digital formation evaluation log generator using a novel physics-informed machine learning (PIML) approach that combines physics-based approaches with machine learning (ML) algorithms. The designed approach consists of blocks that calculate mechanical specific energy (MSE), physical estimates of gamma ray (GR) using physical and empirical models, and formation information. All this information and the drilling parameters are used to build a classification model to predict the formations, followed by formation-based regression models to get the final estimate of GR log. The designed PIML approach learns the relationships between drilling parameters and the GR logs using the data from the offset wells. The decomposition of the model into multiple stages enables the model to learn the relationship between drilling parameters data and formation evaluation data. It makes it easier for the model to generate GR measurements consistent with the rock formations of the subject well being drilled. Because the computationally generated GR by the model is not just dependent on the relationships between drilling parameters and GR logs, this model is also generalizable and capable of being deployed into the application with only retraining on the offset wells and no change in the model structure or complexity. For this paper, the drilling of the horizontal section will not be discussed, as this was done as a separate body of work. Historically collected data from the US Land Permian Basin wells are used as the primary data set for this work. Results from the experiments based on the data collected from five different wells have been presented. Leave-one-out validation for each of the wells was performed. In the leave-one-out validation process, four of the wells represent the set of offset wells and the remaining one becomes the subject well. The same process is repeated for each of the wells as they are in turn defined as a subject well. Results show that the framework can infer and generate logs such as GR logs in real time. The average root-mean-squared error (RMSE) observed from the experiments is 27.25 api, representing about 10% error. This error value is calculated based on the mean estimate and does not consider the predicted confidence interval. Considering the confidence interval helps further reduce the error margin.

Rock Typing and Characterization of the Late Cretaceous Abu Roash "G" Reservoirs at East Alam El-Shawish Field, Western Desert, Egypt

Rock typing and petrophysical characterization play a vital role in constructing reservoir models for petroleum exploration and development. This study focuses on evaluating the petrophysical characteristics of the Late Cretaceous Abu Roash "G" Reservoirs at the East Alam El Shawish field in Egypt's Western Desert. The study involved five vertical wells and employed various techniques and analyses to investigate the reservoir. Lithology determination utilizing well logs and core analysis helps identify the lithology types and corresponding porosity of the Abu Roash "G" reservoirs. Sandstone and limestone lithologies with varying porosity ranges were identified, along with the influence of shale on neutron porosity values. Facies analysis of the Abu Roash "G" Member identified seven lithofacies types, categorized into shallow marine and deeper marine depositional environments. The petrophysical analysis involves evaluating gamma-ray logs, porosity, permeability, flow zone indicator (FZI), and reservoir quality index (RQI) values for each lithofacies type. This analysis classifies the core samples into seven reservoir rock types (RRT1 to RRT7) based on petrophysical attributes, providing a clear classification of the Abu Roash "G" reservoir interval. RRT1, RRT2, and RRT3 exhibit the highest reservoir quality, while RRT4 and RRT5 indicate moderate reservoir quality. RRT6 and RRT7 exhibit low reservoir quality due to unfavorable petrophysical behavior. The findings of this study provide valuable insights into the Abu Roash "G" reservoir, including its lithofacies, reservoir properties, and depositional environments. This knowledge is crucial for reservoir characterization and optimizing oil production strategies in the region.

Evaluating Petrophysical Properties of Sa'di Reservoir in Halfaya Oil Field

The petrophysical characteristics of five wells drilled into the Sa'di Formation in the Halfaya oil field were evaluated using IP software to determine a reservoir and explore hydrocarbon reserve zones. The lithology was evaluated using the M-N cross-plot method. The diagram showed that the Sa'di Formation was mainly composed of calcite (represented by the limestone region) is the main mineral in the Sa′di Reservoir. Using a density-neutron cross plot to identify the lithology showed that the formation mainly consists of limestone with minor shale. Gamma-ray logs were employed to calculate the shale quantity in each well. The porosity at weak hole intervals was calculated using a sonic log and neutron-density log at the reservoir unit. Additionally, Archie's equation is applied to calculate fluid saturation using resistivity data. The reservoir water saturation in the uninvaded zone is calculated using Archie's equation, which determines the most essential element utilized in log evaluation. Finally, the permeability was measured using a flow zone indicator. The results indicate that the limestone and shale that the cuttings description report enhanced comprise most of the Sa'di reservoir. At the HF-316 and HF-21 wells, the core porosity was verified. In an uninvaded zone, the Archie equation offers the best estimation. Three equations were derived from the core data's porosity-permeability connection using a cross-plot of the reservoir quality index and normalized porosity index. According to the general interpretation, zones B1, B2, and B3 contain the most hydrocarbons; however, the B2 zone, the best layer in the Sa'di reservoir, has the highest hydrocarbon concentration. This is close to previous studies and field results. Finally, Sa'di A is formed mainly of mud lime and contains no hydrocarbons. As a result, Sa'di A was separated into A1 and A2 based on the percentage of shale difference.

The SEDIMENTOLOGICAL ANALYSIS, DEPOSITIONAL ENVIRONMENT AND SEQUENCE STRATIGRAPHIC STUDY OF IDA 4, 5, 6 WELLS NIGER DELTA BASIN, NIGERIA

Sequence stratigraphic study divides sedimentary successions into unconformity or maximum flooding surface bounded units (sequence) that form during a single, major cycle of sea-level change. Detailed sedimentological and sequence stratigraphic studies of the strata penetrated by Ida-4, 5, and 6 wells were carried out to deduce the depositional environment and correlate the stratigraphic units. The wells are located in the coastal swamp depobelt of the Eastern Niger Delta. Studied samples were dry-sieved for sedimentological analyses. Each fraction was studied under reflected light microscope. The lithology consists of an alternation of shale and sandstone units. The grain size of the sandstone units consists of fine to medium grains, occasionally coarse to granule-sized grains. Dominant accessories minerals are ferruginous materials, shell fragments, carbonaceous detritus, and few records, of mica flakes, glauconite, and pyrite. Regular sand and shale intercalation pattern on the Gamma Ray log permitted easy recognition of sub-cycles (autocycles) of sedimentation in an extensively developed paralic sequence. Paleoenvironmental reconstruction using accessories minerals recognizes shallow water settings with intermittent deeper water conditions. Rapid sedimentation rates are inferred in the studied area based on the observed alternation of thick sandstone, shale, and mudstone units. The MFS and SB were dated 9.5 Ma and 10.35 Ma respectively. Lithologic and system tracts correlations show lateral continuity of sandstone units (potential reservoirs) depicted in the lithofacies subcycles correlation. This is useful in the determination of reservoir geometry, areal coverage, and calculation of the volume of accumulated hydrocarbon, and directing well trajectory during the drilling operation.

Lithofacies, stratigraphy and depositional history of Middle Muschelkalk evaporites (Zeglingen Formation) in northern Switzerland

In northern Switzerland, Middle Muschelkalk evaporites (Zeglingen Formation) were deposited under arid conditions in the southernmost part of the epicontinental Central European Basin during times of reduced inflow of sea water from the Tethyan realm. Because of their marginal position in the basin, direct and detailed correlation of Muschelkalk sediments of northern Switzerland with equivalent strata in interior parts of the basin is not straightforward. Based on detailed sedimentological logging of 640 m of drill cores from ten wells in northern Switzerland, 22 lithofacies and 10 lithofacies associations were distinguished for the Middle Muschelkalk evaporites. High-resolution regional correlations of gamma-ray logs record substantial thickness variation of the evaporites. Locally, dissolution was recognized by visual core examination that could be dated to Middle Triassic times and that was likely related to subsurface fluid flow along deeper seated faults. In combination with the regional thickness variation, the dissolution phenomena suggest a tectonically active depositional setting in the Middle Triassic. Middle Muschelkalk evaporites consist of nine types of mainly auto-cyclic shallowing- or brining-upward mini-cycles which form a correlatable succession of five distinct 4th order cycle-sets. Despite the tectonically active depositional environment, most lithofacies encountered appear to have nearly flat bounding surfaces. Thus, marine transgressions flooded wide areas nearly simultaneously. The corresponding deposits serve as reference levels to tie the peripheral facies of northern Switzerland into the supra-regional context.

Coal Structure Characteristics of the 2# Coal Seam in the Jiaozuo Mining Area and Its Geological Dependence.

To clarify the coal structure, spatial distribution, and controlling factors of the 2# coal seam in Jiaozuo mining, the drilling coal samples were collected to observe the coal type and coal structure. The coal macerals were identified by a MPVSP microscope photometer, and the spatial characteristics of the coal structure were obtained through interpreting deep lateral resistivity logging, natural gamma ray logging, density logging, and acoustic logging curves. The influence of coal properties, burial depth, geological stress, and faults on the coal structure were discussed correspondingly. The results exhibit that granulitic-mylonite coal was most developed in the 2# coal seam, followed by primary coal and cataclastic coal; the coal type was dominated by semibright coal, followed by clarain and semidull coal. Granulitic-mylonite, cataclastic, and primary coals were the main components of clarain, semibright coal, and semidull coal, respectively. Higher vitrinite and organic matter contents were conducive to the development of granulitic-mylonite. The coal structure combinations were spatially varied, and the granulitic-mylonite combinations were the most common. Granulitic-mylonite coal was developed in the east and south parts of the study area, and the coal structure was fragmented with a greater burial depth and larger thickness. The geological stress is the fundamental cause of coal structure damage as well as the cutting of faults.

The Potash Identification (PID) Plot: A Rapid Screening Crossplot for Discrimination of Commercial Potash

Potash minerals are the primary source of potassium (K), which is used for the manufacture of gunpowder, fertilizer, and as a sodium-seasoning substitute. Commercial potash minerals are all evaporites. Because potassium-40 (40K) is radioactive (decaying to argon-40 (40Ar) and releasing a gamma ray (GR) in the process), commercial potash mineralization is often discovered when GR (γ ray) logs in petroleum wells drilled through evaporite sequences “go off scale.” However, not all potash minerals may be commercial sources of potassium via underground mining techniques, and potassium is not the only radioactive element. For example, the mineralogy of the McNutt “potash” Member of the Salado Formation in southeast (SE) New Mexico is extremely complex, consisting of multiple thin (i.e., less than 10 ft thick) beds of six low-grade (radioactive) potash minerals, only two of which are commercial for underground mining. There are also four nonradioactive evaporite minerals, one of which may interfere with potash milling chemistry and numerous claystones and marker beds (shales and/or volcanics), with GR count rates comparable to the low-grade potash mineralization in this sequence. Because of this complexity, traditional borehole wireline (WL) and logging-while-drilling (LWD) potash assay techniques, such as GR log-to-core assay transforms, may not be sufficient to identify potentially commercial potash mineralization for underground mining (Teufel, 2008) in SE New Mexico. Crain and Anderson (1966) and Hill (2019) developed linear programming and multimineral analyses, respectively, to estimate potash mineralogy and grades from multiple borehole geophysical measurements. However, both of these approaches require large sets of multiple log measurements. In SE New Mexico, petroleum wells are drilled through the Salado Formation evaporite (including the McNutt “potash” Member) with air, then cased and cemented in place without running WL measurements. Then, the wells are drilled out to total depth (TD) in the underlying sediments with water-based mud. Complete log suites are run from TD to the casing shoe, with only the GR and neutron logs recorded through the cased evaporite sequence for stratigraphic and structural correlation. As a result, essentially all recent oil and gas wells in SE New Mexico have casedhole gamma ray and neutron logs through the Salado evaporite. Hill and Crain (2020) developed a simple crossplot involving only GR and neutron log data, which could discriminate between anhydrous and hydrated potassium evaporite minerals. Logs from these wells could provide a rapid potash screening database if used properly. This technique can be used with both openhole and casedhole petroleum well logs, as well as corehole WL logs, and provides discrimination of commercial potash mineralization from noncommercial (potash and non-potash) radioactive mineralization. Case histories of the use of PID crossplots in evaporite basins of Michigan, Nova Scotia, Saskatchewan, and SE New Mexico are described. This technique may also be useful in screening potential potash deposits elsewhere in the world.

Reservoir Quality Related to Diagenetic Development in the Carbonate Mishrif Formation: A Case Study from the X Oilfield, Southern Iraq

The Middle Cretaceous Mishrif Formation is considered as the main productive reservoir, southern of Iraq. The rudist-bearing productive zones are characterized by high heterogeneity due to the effects of diagenesis and the depositional environment. The Mishrif Formation represents a carbonate succession which deposited through the Middle Cretaceous (Cenomanian-Early Turonian) within the main retrogressive depositional period succession. This research is identifying the effect of each diagenetic process on the reservoir properties by using the utility of core data and thin sections collaborated with the well logs data along the wells X-46, X-41 and X-42 in the X oilfield. The Mishrif Formation have been subjected into various diagenetic processes such as micritization, neomorphism, dissolution, cementation, dolomitization and pressure solution or stylolitization. Effect of eight diagenetic processes have been recognized in the Mishrif Formation, these processes have affected constructively and destructively on the reservoir quality of the Mishrif Formation; dissolution and fractures have been affected positively, while micritization, cementation, dolomitization, compaction, bioturbation and neomorphism have a negative affect. The porosity logs (Neutron, Density and Sonic) and Gamma ray log are interpreted to find the porosity and clay content to determine the reservoir quality. The porosity results show a wide variation, the primary porosity is decreased in the well X-46 at the depth of 2300-2450 due to the cementation while the secondary porosity is enhanced due to the dissolution and fractures. In well X-42, at the depth of 2225-2400 m there is an increasing in the porosity due to the increasing of grains to clay ratio, while in the X-42 at the middle to the upper parts, the porosity is very low due to cementation, compaction and micritization processes as well as the high content of clay. In general, the porosity is enhanced in the reefal zones due to the geometry nature of the pore throat which increasing both of the effective porosity and permeability.

Petrophysical Analysis Based on Well Logging Data for Tight Carbonate Reservoir: The SADI Formation Case in Halfaya Oil Field

Carbonate reservoirs are an essential source of hydrocarbons worldwide, and their petrophysical properties play a crucial role in hydrocarbon production. Carbonate reservoirs' most critical petrophysical properties are porosity, permeability, and water saturation. A tight reservoir refers to a reservoir with low porosity and permeability, which means it is difficult for fluids to move from one side to another. This study's primary goal is to evaluate reservoir properties and lithological identification of the SADI Formation in the Halfaya oil field. It is considered one of Iraq's most significant oilfields, 35 km south of Amarah. The Sadi formation consists of four units: A, B1, B2, and B3. Sadi A was excluded as it was not filled with hydrocarbons. The structural and petrophysical models were built based on data gathered from five oil wells. The data from the available well logs, including RHOB, NPHI, SONIC, Gamma-ray, Caliper, and resistivity logs, was used to calculate the petrophysical properties. These logs were analyzed and corrected for environmental factors using IP V3.5 software. where the average formation water resistivity (Rw = 0.04), average mud filtrate resistivity (Rmf = 0.06), and Archie's parameters (m = 2, n = 1.9, and a = 1) were determined. The well-log data values calculated the porosity, permeability, water saturation, and net-to-gross thickness ratio (N/G).

Identification of Coal Distribution Pattern Using Well Logging Method Based on Gamma Ray Log Data and Log Density in Area X PT PMC Site Sungai Lilin

Identification of Coal Distribution Pattern Using Well Logging Method Based on Gamma Ray Log Data and Log Density in Area X PT PMC Site Sungai Lilin

Increasing the capabilities of stationary neutron logging in determining the lithology of the carbonate section

The article presents a method of lithological identification of dolomites and limestones ac-cording to stationary neutron logging in several oil wells located on the territory of the Republic of Bashkortostan. The article presents a research of the influence of the mineral skeleton of rocks on the readings of stationary neutron logging and the use of differences in the values of porosity coefficients calculated from the readings of individual probes for the lithological identification of dolomites and limestones. Keywords: porosity; compensated neutron logging; neutron-neutron thermal neutron logging; neutron gamma-ray logging; lithological identification; carbonates; limestone; dolomite.

Hydrocarbon Formation Evaluation Using Well Log Data Of Well Tmg-02, Opolo Field, Niger Delta

Well TMG-02 with the depth interval of 5058.77 to 9389.43ft of Opolo field located in the Niger delta was assessed for hydrocarbon using suite of geophysical well logs. Suite includes gamma ray (GR), formation density (RHOB), neutron porosity (NPHI), and resistivity logs. The analysis was carried out to estimate the field’s hydrocarbon prospect by identifying hydrocarbon bearing reservoirs and their properties. The quantitative and qualitative results, identified thicker units of sand than shale lithology, three reservoirs A, B, C within the depth ranges from 5058.77ft to 9389.43ft, capable of accumulating hydrocarbon based on the petrophysical parameters calculated were delineated. The effective porosity for each of the reservoir are: 27%, 24% and 19% respectively. It was observed that reservoir A, B had excellent permeability while reservoir C was low as a result of thicker shale sequence within the reservoir. The result obtained shows presence of hydrocarbon bearing gas water contact in Reservoir A at depth of 5119.70ft, gas oil contact and oil water contact at depths 7310.00ft and 7438.69ft in Reservoir B and Gas water contact at depth 9032.00ft at Reservoir C.

Sedimentary Environments and Paleoclimate Control of the Middle Miocene Balikpapan Group, Lower Kutai Basin (Indonesia): Implications for Evaluation of the Hydrocarbon Potential

Sedimentary organic matter concentrated in source rocks forms the main source for the formation of hydrocarbons. Its deposition and preservation are strongly controlled by the depositional environment and paleoclimate. This study evaluates the paleoenvironment and the paleoclimatic controls of sediments in the Middle Miocene Balikpapan Group, Mahakam Delta of the Lower Kutai Basin, Indonesia. The sedimentary succession of the Mentawir Formation, encountered in three wells (MHK 1, MHK 3, and MHK 4), contains interbedded sandstones, siltstones, shales, and coal. Gamma ray log analysis has revealed four facies associations: (a) funnel-, (b) bell-, (c) cylindrical-, and (d) bow-shaped patterns, which, together with sedimentological and mineralogical analysis, suggest a fluvio-deltaic depositional environment during the Middle Miocene in the study area. Sedimentary successions from wells MHK 1 and MHK 3 comprise interbedded sandstone and siltstones and are interpreted to represent repeatedly occurring delta plain, delta front, and prodelta deposits. The succession encountered in well MHK 4 mostly consists of amalgamated sandstones and indicates a predominantly fluvial to upper delta plain environment with distributary channels and crevasse splays interbedded with only thin delta front deposits. X-ray diffraction–clay fraction analysis shows that the <2 μm clay-sized fraction consists of kaolinite (38%–67%), illite (14%–29%), chlorite (2%–17%), and mixed-layer illite/smectite (I/S) (14%–30%). Kaolinite formation and abundance indicates a hinterland climate classified as type Af (tropical rainforest) and intensive chemical weathering conditions in the source areas related to tropical to sub-tropical climates with high precipitation. Under such climatic conditions, kaolinite and I/S mixed-layer minerals are preferentially formed because the characteristic ions, K+, Na+, Ca2+, and Fe2+, are leached away. Thus, the production, transport, distribution, and preservation of sedimentary organic matter in the onshore Mentawir Formation of the Balikpapan Group are predominantly controlled by the humid tropical climate and fluvio-deltaic processes.

Prediction of Petrophysical Properties using Post Stack Seismic Inversion and Geostatistical Techniques over F-3 Block, Netherlands - A Comparative Study

To estimate petrophysical parameters, seismic inversion techniques have been frequently used for estimating attributes like P-impedance, elastic impedance, S-impedance, density, Vp / Vs ratio, and gamma-ray logs from seismic and well-log data. These characteristics enable us to comprehend subsurface lithology for geo-seismic analysis, including its extent and shape. Four different post-stack inversion techniques, including bandlimited inversion (BLI), colored inversion (CI), maximum likelihood sparse spike inversion (MLSSI), and model-based inversion (MBI), have been applied to the post-stack seismic data from the F3 block in the Netherlands in this study. The objective is to compare the efficacy of these inversion methods over F3 block seismic data. For post-stack inversion, the data was inverted into a very high-resolution P-impedance volume. The analysis depicts that all four inversion methods provide mutually consistent subsurface information with marginally better MBI results. Furthermore, geostatistical techniques have been used intensively for further testifying the results obtained from post-stack inversion methods. The geostatistical techniques use seismic data-derived attributes and inverted impedance-derived attributes as input to estimate P-wave velocity, porosity, and density away from the boreholes. Two geostatistical methods namely probabilistic neural network (PNN) and multilayer feed-forward neural network (MLFN) are used for the analysis. Porosity, density, and P-wave velocity have been predicted using both techniques which highlighted different characteristics of the subsurface with very detailed information. The derived results show that reservoir properties have been better estimated with the combination of MBI and PNN techniques for F3 block data over the other methods used in this study.

Structural health monitoring of sabo check dams with cosmic-ray muography

Debris dams have a crucial role in consolidation of river basins and allow erosion control, flood protection in mountainous areas. Many of these infrastructures have operated over five decades, thus structural health monitoring (SHM) of these infrastructures became timely due to their aging. Utilizing new techniques is required for inspecting a large number of dams and deciding about their reinforcement or reconstruction. In this work, we propose cosmic-ray muography as a complementary tool for the SHM of debris dams. We conducted the first muographic surveying of a sabo check dam in the Karasu River, Gunma, Japan. The average mass density image was produced with a spatial resolution of 0.5m through the dam. The comparison of density data reconstructed by muography and gamma-ray logging suggest the internal deterioration of dam in the region where cement released out from the embankment body.