Sandy Shale Research Articles

Skin Factor Test Experiment of the Combined Structure of Blind and Screen Pipes

During the drilling process of horizontal wells in offshore oil fields, when encountering highly clayey shale or sandy shale sections, a common practice is to use a combination of blank pipes and screen pipes in the completion column to isolate high clay content layers. This helps prevent significant clay blockage in the screen pipes or wellbore, thereby reducing production loss. However, when blank pipes cannot effectively isolate clayey or sandy shale sections, the migration of clay content can lead to screen pipe blockage, adversely affecting production capacity. Given the current lack of evaluation methods for the impact of combined blank and screen pipe completion columns on production capacity, an experiment was designed to evaluate the skin factor of the completion column with a combination of blank and screen pipes. Through the calculation of the skin factor, the variation patterns of the skin factor for completion columns with blank and screen pipes under different conditions were obtained. These findings were then applied to a production evaluation. The research results revealed the following: (1) As the proportion of blind pipes increases, the skin factor of the combination of blind pipes and screen pipes in the completion tubing also increases. Excessive blind pipe ratios reduce production capacity. (2) In cases where the annular space is not completely filled, the influence of the blind pipe proportion on production capacity can be negligible. However, when the annular space is 100% filled, a higher proportion of blind pipes and silt content results in a larger skin factor, which leads to reduced production. In the application of the XH horizontal well case study, using the calculated model for the skin factor of the combination of blind pipes and screen pipes in the completion tubing established in this paper, it was determined that when the annular space was not completely blocked and 20 m of blind pipes were not placed in the designated position, the impact on the production index was 0.73%. However, when the blind pipes were not placed in the designated position for 100 m, the impact on the production index reached 1.47%. The method developed in this paper provides theoretical guidance for the optimization of completion tubing in mudstone and sandy mudstone sections and for production evaluation.

Estimation of Groundwater Potential and Aquifer Protective Capacity Within Old Ikenga Hotel, Nsukka, Enugu State, Nigeria

A geophysical survey using electrical resistivity method was conducted around Old Ikenga Hotel, Nsukka in Enugu State, Nigeria to investigate the groundwater potential and aquifer protective capacity of the area. The project area lies within latitudes 6°50'4.0''N – 6°57'52.0"N and longitudes 7°21'6.3"E – 7°28'12.0"E, and covers an area of about 89.6 km2. Vertical Electrical Soundings (VES) were carried out with a digital read out resistivity meter (ABEM SAS 1000). The VES points were marked at 25 m and 75 m along a 100 m line. A total of eight soundings were carried out in the area. The VES data collected were interpreted using INTERPEX software and the results presented in terms of resistivity, thickness, depth and lithology. The lithology was inferred by correlating the result to the lithology log of the borehole drilled in the hotel and the geology of the study area. The VES result shows lithologic layers varying from 4 to 5. Aquiferous sand and Aquiferous sandy shale constitute the aquifer units in the area at depth of 30.26 m to 188.20 m, with their thickness ranging from 30 m to 74 m as shown by their isopach map. The aquifer protective capacity was determined by calculating for longitudinal conductance and matching the values to known standards. The calculated longitudinal conductance varies from 0.0409 to 3.1235 mhos. The interpreted VES results reveal poor, moderate, good and very good aquifer protective capacities of the overburden layers.

Electrical Resistivity Tomography (ERT) Investigation for Landslides: Case Study in the Hunan Province, China

Electrical resistivity tomography is a non-destructive and efficient geophysical exploration method that can effectively reveal the geological structure and sliding surface characteristics inside landslide bodies. This is crucial for analyzing the stability of landslides and managing associated risks. This study focuses on the Lijiazu landslide in Zhuzhou City, Hunan Province, employing the electrical resistivity tomography method to detect effectively the surrounding area of the landslide. The resistivity data of the deep strata were obtained, and the corresponding geophysical characteristics are inverted. At the same time, combined with the existing drilling data, the electrical structure of the landslide body is discussed in detail. The inversion results reveal significant vertical variations in the landslide body’s resistivity, reflecting changes in rock and soil physical properties. Combined with geological data analysis, it can be concluded that the sliding surface is located in the sandy shale formation. Meanwhile, by integrating various geological data, we can conclude that the landslide is currently in a creeping stage. During the rainy season, with rainfall infiltration, the landslide will further develop, posing a risk of instability. It should be promptly addressed through appropriate remediation measures. Finally, based on the results of two-dimensional inversion, this article constructs a three-dimensional surface morphology of the landslide body, which can more intuitively compare and observe the internal structure and material composition of the landslide body. This also serves as a foundation for the subsequent management and stability assessment of landslides, while also paving the way for exploring new perspectives on the formation mechanisms and theories of landslides.

Prediction of Inter-Well Petrophysical Properties from Seismic Model: A Case of Egbem Field, Niger Delta, Nigeria

We have generated a seismic model for the prediction of inter-well petrophysical properties of Egbem Field; in the Niger Delta, Nigeria. Acoustic Impedances (AI) were calculated from sonic and density logs in the available 24 wells. Reflection Coefficients (RC) determined from the acoustic impedances were convolved with modelled wavelet to produce synthetic seismograms at various well locations. A top structure map of a reservoir from the field was used to define the position of faults, which served as key pillars in gridding the reservoirs of the field into geocellular blocks of 50 x 50 meters each. Petrophysical analysis of the field showed an average porosity of 24.8% and volume of shale of 19.9%. Petrophysical parameters were geostatistically distributed on the generated framework model using Sequential Gaussian Simulation (SGS). The result of the Acoustic Impedance classification reveals four lithologic facies namely, shale, sandy shale, shaley sand and sand facies. The facies model indicates high and low acoustic impedances for sand and shale respectively. This model indicates that sand which is a good reservoir is concentrated in the central part of the field. The result of synthetic seismic generation showed a very good match between acoustic impedance and lithology. Comparison of porosity obtained from the porosity model with conventional well log porosity showed similarities in their histogram distribution. Finally, Three-dimensional seismic model of Egbem Field has been constructed using log data from twenty four wells. The application of geostatistical analyses extrapolated and interpolated these log data to cover the entire field.

Fractionation of rare earth elements in soil profiles along an elevation gradient in central Taiwan

The distribution of rare earth elements (REEs) in soils is affected by climate, which is one of the main factors controlling soil formation. However, variations in the geochemical behavior of soil REEs with pedoclimatic changes have rarely been investigated. This study determined the mobilization/retention and fractionation of REEs in nine soil profiles derived from sandy shale along an elevation gradient from 49 m to 2394 m above sea level in the Central Mountain Range of Taiwan. The experimental results indicated a gradually decreased ΣREEs trend with increasing elevation/rainfall. Clay content significantly (p < 0.05) correlated with REEs, which accumulated in argillic horizons. Moreover, a decreasing GdN/YbN ratio with increasing secondary minerals (i.e., clay and pedogenic Fe and Al oxides) implied their preferential sequestration tendency for heavy REEs over light REEs. This preferential association coupled with intensifying illuviation along the climatic gradient, resulted in increasing LaN/SmN and decreasing GdN/YbN ratios with increasing weathering degree and elevation (p < 0.01). Our results demonstrate that in the studied humid tropical region, increasing moisture availability caused by higher rainfall and lower air temperatures with rising elevation has led to stronger illuviation and more advanced soil development, which is reflected in REE fractionation and can be quantified by the ratios GdN/YbN and LaN/SmN.

Stratigraphic Analysis of the Nahr Umr Formation in the Luhais Oil Field, South Iraq

The Nahr Umr Formation, which is Albian-Early Turonian in age, was investigated in the Nahr Umr Formation succession at two wells of the Luhais oil field in southern Iraq. The study defined sedimentary facies, types, and distribution of porosity and their relationship to sedimentary facies, as well as different types of diagenetic processes. It also included the distribution of facies in the Nahr Umr Formation in relation to suggested depositional settings. Thin sections of the cores from the two chosen boreholes (Lu 39 and Lu 43) in the Luhais Oil Field were used to study the petrography and lithofacies of the Nahr Umr Formation. The five fundamental facies identified in this study are poorly and well-sorted, quartz arenite sandstone, in additional to clayey sandstone poorly sorted, sandy shale, and shale, it represented many sub-environments present in the delta plain depositional environment, the distributary channel depositional environment, and the delta front depositional environment. The Nahr Umr succession in the examined wells (Lu -39 and Lu-43) in the Luhais oil field, southern Iraq, has three asymmetrical cycles of the third order, which are identified by the variable frequency as well as the symmetry of the relative sea level. They show successive events involving sea-level rise and stillstand. In the study area, the succession is formed by surface erosion, which represents the boundary of the sequence type 1 (SB1) distinguished in all wells of the study. As a result of the significant drop in the relative sea level during the stage of the marine retreat (regressive), which indicates coarsening-shallowing upwards and with continuous decreasing, a sequence boundary of type 2 (SB2) is formed at the end of this tract. The boundary of SB2 represents the decrease in sea level, indicating the beginning of the second stratigraphic sequence, which shows the deposition of sand in the river channels as it reflects progressive accretion patterns towards the basin represented by (MFST. Then the sediments begin to thin, and the shale layer appears at the Nahr Umr Formation top, which reflects the regional marine progress and marks the sedimentation of the limestone formation that separates it from the Nahr Umr Formation on the regional flood surface.

Petrophysical Properties and Identification of Electrofacies from Well Log Data of Nahr Umr Formation in Subba Oilfield, Southern Iraq

The main purpose of this study is to identify electrofacies and evaluate the petrophysical properties of the Nahr Umr Formation in four wells: A, B, C, and D in the Subba oilfield, southern Iraq. The petrophysical properties, such as shale volume, porosity, water saturation, hydrocarbon saturation, and bulk water volume, were computed and interpreted using Techlog software. According to the interpretation of density, neutron, and gamma ray sonic logs and deep resistivity logs using the IPSOM technique, four electrofacies were identified as sandstone, shaly sand, sandy shale, and shale electrofacies. The formation was divided into three parts based on well log interpretation and petrophysical analysis: the upper part, middle part, and lower part Interpretation of formation lithology and petrophysical parameters shows that the lower part consists mainly sandy shale with layers of sandstone and shale high porosity and high oil saturation whereas middle part consists mainly of sandstone, alternating with thin bedded of sandy shale and shale with high porosity and medium oil saturation. The upper part consists mainly of a sandy shale alternating with shale and shaly sand with high porosity, hydrocarbon saturation, and lower water saturation.

Measurement of Gas Diffusion Coefficients in Cores of Fine-Grained Lithologies Considering Stress and Adsorption Effects.

Matrix diffusivity is vital for developing tight sandstone and shale gas reservoirs. This study proposes a method to test the diffusivities of a core under confining pressure conditions using the gas diffusion technique. The diffusivities of methane and helium were examined in fine-grained rocks (sandy shale, silty sandstone, tight sandstone, and shale) under specific stress conditions. The results revealed that the gas diffusivities varied among the samples. The tight sandstones exhibited diffusivity higher than that of silty sandstone, sandy mudstone, and shale. Helium diffusivities in shales and sandy mudstones were 1 order of magnitude smaller, while methane diffusivities were 2 orders of magnitude smaller than those in tight sandstones. A positive correlation was observed between the stress sensitivity factor and the clay mineral content, indicating the influence of the clay minerals' mechanical properties. Additionally, the shale gas diffusivities exhibited significant anisotropy due to slit-like gas channels parallel to laminae in shale. It was found that the impact of adsorption on diffusivity was positively correlated to the amount of adsorption. While the adsorption effect was negligible in tight sandstones, organic-rich shales and sandy mudstones experienced an order-of-magnitude reduction in methane diffusivities compared to helium. This study presents a method to evaluate the diffusion coefficient of a core matrix under a confining pressure. It provides insights into gas diffusion behavior in different fine-grained rocks, considering the effects of stress, clay mineral content, and adsorption. These findings contribute to understanding tight sandstone gas and shale gas reservoirs, aiding in the optimization of gas production strategies.

A simplified log creep model for describing triaxial creep of mélange rocks

This study aims to develop a simplified log creep model (LgCM) for predicting the triaxial three-stage creep behaviors of mélange rocks. The model was deduced from the creep deformation mechanism by considering the competition of strain rate hardening and damage during the steady and accelerating creep stages and was described by two simplified fractal functions. The model was then compared with the previous creep models on the uniaxial three-stage creep data of mortar, rock salt, and sandy shale, as well as the triaxial low-stress creep data of claystone. Afterward, the triaxial creep experimental results of the mélange rock samples were introduced to illustrate the process of calibrating the model in predicting the triaxial three-stage creep behaviors of mélange rocks. It was found the developed LgCM model showed good performance in predicting both the uniaxial and triaxial three-stage creep behaviors of rocks. The investigation reveals that the trend of the parameter β can indicate three thresholds of the hardening and damaging effects, and provide the equation to reproduce the creep behavior of the mélange rock. The work contributes to understanding the time-dependent failure of underground rock mass in mélange rock formations.

Study on the failure characteristics of overburden and the evolution law of seepage field in deep buried thick coal seam under aquifers

Water inrush at roof area seriously affects the safety of coal mines. The characteristics of aquifer and aquiclude at Wutongzhuang Mine are analyzed. Considering the effect of seepage field, a formula for calculating the height of water-conducting fractured zone (HWCFZ) in deep buried thick coal seam mining is derived. A damage-seepage coupling model with rock porosity and damage factor as independent variables is established. FLAC3D is re-developed by using FISH language, and the fluid–solid coupling calculation model of deep buried thick coal seam mining is established. The evolution law of the plastic zone, seepage field and water-conducting fractured zone (WCFZ)of the overburden in the gob with the advancement of the working face is analyzed, the main conclusions are as follows: With the continuous advancement of the working face, the distribution shape of the plastic zone and seepage field has changed from a trapezoidal to a saddle shape; when the working face reaches full mining, the maximum heights of the caving zone, fractured zone and HWCFZ are 24 m, 113 m, and 123 m, respectively; The 50 m-thick sandy shale aquifer is penetrated by the WCFZ, and the WCFZ on the side of the working face above the gob is the main water channel when the working face is advanced to 220 m. The on-site monitoring results showed that mine water inflow is not affected by surface rainfall and the 50 m-thick sandy shale is successively connected by the WCFZ. The results of comprehensive research showed that the HWCFZ cannot be calculated by traditional formulas when mining deep buried thick coal seams.

Sedimentology and Mineralogy of Sedimentary Sequences in Nanim Field in the Niger Delta basin, Nigeria.

A total of nineteen ditch cuttings from the sedimentary sequence of Nanim Field, were subjected to both sedimentological and mineralogical analysis with the aim of investigating the mineralogical composition of the studied section (1810 m - 2650m) in the study area. The shale samples were grinded, pulverized and sieved with less than 75μm and analyzed using X-ray diffraction techniques (XRD) for mineralogical composition. Results of the sedimentological analysis, suggests four lithofacies made up of sandstone, shaly sand, shale and sandy shale in he studied section. The studied section has been interpreted as a shallow marine environment &nbsp;divided into two broad lithofacies sequences made up of beach sand (1810 m - 2290 m.) and upper shoreface (2300 m – 2650m) respectively. The beach sand sequences comprises thick sands, brownish, grey to black, fine to coarse grained, whereas the upper shoreface sequence is essentially a heterogeneous sequence of alternating sand medium to very fine grained sand and shale - grey. Results from the XRD analysis shows that the mineralogical composition of the basal part (upper shoreface) of the studied section is characterized by kaolinite a dominant in sediments of fluviatile environments and is known to concentrate in many near-shore sediments (shallow marine) with a decrease in abundance from the shoreline as other clay minerals increase basinward.

Uniaxial Creep Test Analysis on Creep Characteristics of Fully Weathered Sandy Shale

The creep damage behavior of rocks is very important for evaluating the stability and safety of key rock engineering. Based on the Lianhua Tunnel Project in China, this paper aims to study the creep damage mechanics, the influencing factors and the creep constitutive models of sandy shale. In order to achieve these goals, a uniaxial compressive strength test and a creep test under different moisture contents and load levels were carried out. According to the test results, the creep parameters (elastic coefficients E1 and E2 and viscosity coefficients η1 and η2) of the Burgers Model were achieved, and the relationship between the creep parameters and moisture content, ω, was established accordingly (E1 = f(ω), E2 = f(ω), η1 = f(ω), η2 = f(ω)). A fully weathered sandy-shale creep constitutive model considering moisture content was finally obtained. Test results showed that creep deformation increases with any increase in load level or moisture content, and the influence of moisture content is more significant. For instance, creep deformation increased by 35% when the load increased by 50%, and creep deformation increased by 82% when the moisture content increased by 45%. In addition, the creep rate in the steady stage and the duration of the primary creep stage increased with any increase in moisture content or load level. The higher the moisture content, the greater the influence of creep deformation on the total deformation. The creep model of fully weathered sandy shale showed that the elastic coefficients (E1, E2) and the viscosity coefficients (η1, η2) are negatively correlated to moisture content; E1 is negatively correlated to load level; and E2, η1 and η2 are positively correlated to load level. Qualitative and quantitative analysis of fully weathered sandy shale can improve the existing research of creep properties and is expected to provide theoretical support for treatment of large deformation disasters in the fully weathered sandy-shale stratum.

Evaluation of CO 2 sealing potential of heterogeneous Eau Claire shale

Abstract During geological carbon dioxide storage in deep saline aquifers, buoyant CO 2 tends to float upwards in the reservoir overlaid by a low permeable formation called a caprock. Caprocks should serve as barriers to potential CO 2 leakage that can happen through diffusion and permeation through faults, fractures or pore spaces. The leakage through intact caprock would mainly depend on its permeability and CO 2 breakthrough pressure and is affected by the heterogeneities in the material. Here, we study the sealing potential of a caprock from the Illinois Basin – Eau Claire shale, with sandy and clayey fractions distinguished via electron microscopy, grain/pore size analyses and surface area characterization. The direct measurements of permeability of sandy shale provide the values on the order of 10 −15 m 2 , while clayey specimens are three orders of magnitude less permeable. The CO 2 breakthrough pressure under in situ stress conditions is 0.1 MPa for the sandy shale and 0.4 MPa for the clayey counterpart – these values are higher than those predicted by the porosimetry methods performed on the unconfined specimens. Sandy Eau Claire shale would allow penetration of large CO 2 volumes at low overpressures, while the clayey formation can potentially serve as a caprock in the absence of faults and fractures.

Reservoir Lithology Identification Based on Improved Adversarial Learning

Reservoir lithology identification is critical to reservoir characterization, reserves calculation, and geological modeling. The deep learning lithology identification method is a data-driven algorithm for establishing the relationship between lithology-sensitive properties and litho-types from a large amount of observed data. The lithology label is inadequate for high drilling and core recovery costs. Consequently, we propose a reservoir lithology identification method based on improved adversarial learning to relieve the overfitting problem and the multi-solution problem caused by inadequate labeled data and massive learnable parameters in training. Firstly, a probabilistic lithology classification neural network (PLCNN) is constructed to predict lithology from density, P-velocity, and S-velocity. In addition, we design an improved adversarial learning (IAL) lithology identification workflow to train the PLCNN with limited labeled data and large-scale unlabeled data. In the workflow, a lightweight discrimination network is established to ensure that the prediction result of the PLCNN is consistent with the data distribution characteristics of real underground lithology. Finally, the proposed method is successfully applied to the Book cliffs model. Compared with the conventional supervised learning workflow, the misclassification of sand and sandy shale can be relieved efficiently with the IAL workflow, and the classification accuracy can be improved to 92.71%.

Field Characteristics of Sedimentary Rocks in the Dohol Formation, Johor, Peninsular Malaysia

The Dohol formation is predominantly composed of sedimentary rocks; however, the black shales attract much attention because of their potential to generate hydrocarbons. Black shales generally have a high organic matter content and can serve as good source rocks for hydrocarbon generation. Therefore, this study was conducted to characterize the sedimentary rocks, including the black shales, which are of great importance and discover new areas where these rocks can be located. Four distinctive lithofacies of shales were observed on the field; the massive black shales facies, light grey shales facies with quartzite intrusion in some areas, the red sandy shales, and the dark brown shales facies. The black shales are dark-coloured, laminated, and some parts are fissile. The second type of shale, light grey, looks similar to the dark shales, but it probably contains less organic matter. In other areas, these grey shales have intrusions of quartzite. The third type of shale facies are the red shales which are sandy, fissile, and highly weathered, and pebbly sands overlie it. Finally, the dark brown shale facies are fissile, flaky, and weathered. The sandstones encountered are massive cream-colored, and composed of mainly quartz with a few scour marks in some areas. Several new outcrop locations of these sedimentary rocks were discovered, and they are spread across Jemaluang, Kota Tinggi, and the outskirts of Mersing town in East Johor. From the outcrop trends and the sedimentary features of the shale rock sequence, the deposition environment of the shales is probably from shallow to deep marine.

Characterization of Subsurface Lithology and Aquifer Parameters Using Vertical Electrical Sounding (VES) for Groundwater Development in Igbo-Imabana, Southern Nigeria

Vertical Electrical Soundings (VES) using Schlumberger array was carried out at fifteen (15) different points to evaluate aquifer characteristics within Igbo-Imabana, Abi L.G.A of Cross River State. Resistivity meter and its accessories were used for data acquisition. The maximum current and potential electrode distance were 400 m and 20 m respectively. The field data were interpreted using Interpex software and three to five geo-electric layers encountered within the study area. The dominant curve type was H followed by K. From the result, geo-electric layers delineated were sandstone, clay, saturated sandstone, sandy shale, clayey shale, and shale with average apparent resistivity values of 2249.94 Ωm, 2.86 Ωm, 365.28 Ωm, 222.69 Ωm, 14.60 Ωm and 59.02 Ωm respectively. The top geoelectric layer was dominantly lateritic topsoil, with variation in degrees of compaction and having an average resistivity of 876.33 Ωm with depth and thickness generally less than 5 m. The calculated aquifer parameters hydraulic conductivity (Kc), transmissivity, longitudinal conductance, and transverse resistance from the VES results show ranges values; 3.86×10–4 to 4.69×10–2 m/day, 2.95×10–3 to 2.82 m2 /day, 2.95×10–3 to 2.81 Ωm and 484.33 to 19444.83 Ω2 m respectively. The aquifer thickness and depth values range from 3.60 m to 68.05 m and 5.20 m to 76 m respectively. The study reviewed that the area is made of heterolithic/heterogenou lithofacies, confined aquifer(s), shallow and deep aquifer. Also, from the models and aquifer parameters, the area is characterized by semipervious materials. This integrally explains why the area have have low transmissivity and majority of boreholes drilled in the area failed.

Lithofacies analysis and Depositional Environment of Eocene – Paleocene Sediments of Ewekoro Quarry SW, Nigeria

The genetic relationship between depositional processes and rock properties (like lithofacies) provide a potentially powerful tool for interpreting ancient depositional environments. The study aims at a more detailed lithologic and Petrographic description of the sediments of this formation in other to acertain the chemical characteristics of the limestone so as to better delineate its uses both industrially, agriculturally and other applications. Seven samples were collected from Ewekoro quarry on the Latitude of 60481N- 60531N and Longitude of 30351E-30401E south western part of Nigeria. The sediments were subjected to lithologic description and petrographic analysis. The lithologic description was carried out with the aid of binoculars microscope, this shows the following lithologies are present sandy shale, shale, marl, limestone, and sandstone. Petrographic analysis shows that the limestone consists of 90-99% calcite, 0-2% quartz as its constituent minerals, sample NSA2 is mainly Sparitic limestone and sample SSA1 is mainly Micritic limestone. The sandstone composition are 50- 65% quartz, 0-5% feldspar and the calcite serve as the cement and it is about 10-32% of the rock volume. Microfossils account for 10-18%. The sediments were deposited in shallow environment based on the presence of ichnofossils (burrows), micro gastropod shells and other broken shells. From the mineralogy, the calcite crystals are suggests a fresh water vadoze environment while the Sparry calcite shows evidences of diagenesis within the formation. The relative age of foraminifera present indicate a Palaeocene/Eocene boundary to Lower Eocene and a lagoonal to inner neritic environment with little influence of marine transgression. Ewekoro limestone is well suited as a raw material for fertilizer besides its general usuage for cement manufacturing.

Exploring seismic detection and resolution thresholds of fault zones and gas seeps in the shallow subsurface using seismic modelling

Seismic resolution and illumination issues are sources of challenges in the detailed imaging and detection of subsurface fault architecture and fluid migration. Improved constraints on resolution can provide input into monitoring requirements and detectability of CO2 leakage, and fault-sealing properties during subsurface visualization of migration pathways. This study explores detection and resolution thresholds via synthetic seismic imaging of a detailed shallow normal fault model with realistic fault architecture including sub-seismic structures of damage zones. The base fault model is built from interpretations of high-resolution P-Cable seismic data and is further developed and conditioned by outcrop-based observations and empirical laws for fracture and deformation band distribution. Damage zones of sandstone layers host deformation bands contrary to shale layers with fractures, while mixed lithologies (shaley sandstone and sandy shale) are subjected to a combination of the two deformation mechanisms. We utilize a 2D point-spread function based convolution seismic modelling to produce the synthetic seismic images. Test scenarios include one baseline fault model without a damage zone (M1), and five more advanced/detailed fault models incorporating features known from outcrops (M2-M6; damage zones, an isolated fracture corridor, and gas seeps (CO2) along damage zones of faults and in the fracture corridor). Furthermore, sensitivity analyses on two selected models test the effect of changing the illumination angle and wavelet. The results show that: (1) faults with damage zones have larger disturbances in seismic signals than faults without damage zones, (2) stronger amplitudes are distinguished for models with CO2-filled fractures, (3) a fracture corridor (5 m at it widest) is clearly visible where it crosses horizons bounding horizontal layers, (4) sensitivity tests show good imaging for illumination ≥45°, which is the average dip of the main fault segment, and (5) learnings from fault modelling offer guidance for seismic monitoring.

Estimation of reservoir properties based on core plugs, lithofacies, and well logs for Nahr Umr Formation in Noor oilfield, southern Iraq

The Nahr Umr Formation, one of the most important Cretaceous formations and one of the main generating reservoirs in southern Iraq and neighboring regions, was chosen to study and estimate its petrophysical properties using core plugs, lithofacies, and well logs from five wells in the Noor oilfield. Reservoir properties and facies analyses are used to divide the Nahr Umr formation into two-member (limestone in the upper part and main sandstone in the lower). Limestone members are characterized by low reservoir properties related to low effective porosity and permeability while the main sandstone member is considered as a reservoir. Four lithofacies were recognized in the main sandstone member of the Nahr Umr Formation according to petrographic observation with gamma-ray. They are well-sorted quartz arenite sandstone, poorly sorted Quartz arenite sandstone, Sandy shale, and Shale Lithofacies.&#x0D; Calculation of the various reservoir properties (shale volume, effective porosity, permeability, and water saturation) using the (Interactive Petrophysics v3.5) program and linking them with the lithofacies by computer processed interpretation (CPI) of available of the available wells. Divided the sandstone member into three units are A, B, and C. Each unit consists of many reservoir sandstone subunits separated by shale and streaks of limestone. Average reservoir properties of units A and B are good to very good related to high porosity, permeability, and economy hydrocarbon saturation (low water saturation). While these properties are decreased in unit C. The Sandston member of borehole No-5 was the best reservoir characterization, especially in the thickness of the reservoir units and the low shale content.

A review of Pakistani shales for shale gas exploration and comparison to North American shale plays

Recent advancements in technologies to produce natural gas from shales at economic rates has revealed new horizons for hydrocarbon exploration and development worldwide. The importance of shale oil and gas has aroused worldwide interest after the great success of production in North America. In this study, different marine source rocks of Pakistan are evaluated for their shale gas potential using analogs selected from various North American shales for which data have been published. Pakistani formations reviewed are the Datta (shaly sandstone), Hangu (sandy shale), Patala (sandy shale), Ranikot (shaly sandstone), Sembar (sandy shale) and Lower Goru (shaly sandstone) formations, all of which are known source rocks in the Indus Basin. Available geological data of twenty-six wells (e.g., geological age, depositional environment, lithology and thickness), geochemical data (e.g., total organic carbon (TOC), vitrinite reflectance (Ro), rock pyrolysis analysis and maturity), petrophysical data (e.g., porosity and permeability) and dynamic elastic parameters estimated from logs (Young’s modulus and Poisson’s ratio) have been investigated. According to this study, the Pakistani shales are explicitly correlated with the most active shale gas plays of North America. The burial depths or geological position of the Pakistani shales are generally comparable to or slightly higher than the North American shales based on the available data. The thicknesses of the Pakistani (except for the Sembar shale) and North American shales fall in similar ranges. In terms of mineralogical composition, all of the Pakistani shales except the Ranikot and Hangu shales have quartz contents in the 40% to 50% range (approximately), which is similar to most of the North American shales. The high maximum TOC of the Hangu and Sembar shales (10%) is comparable to the New Albany, Antrim and Duvernay shales. The maximum TOC values for the Ranikot (3%), Lower Goru (1.5%) and Datta (2%) shales are lower than all North American shales. The TOC of Patal Shale (∼5%–10%) is comparable to Fayetteville and Eagle Ford shales. The geological and geochemical parameters of all the Pakistani shales reviewed in this work are promising regarding their shale gas prospects. However, geomechanical data are required before conclusions on these shales’ economic production can be made with confidence.