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The early Eocene carbonate reservoir, Sui Main Limestone (SML), is the largest gas reservoir in Pakistan. In the Qadirpur area, more than 30 wells have been drilled, some of which have been declared dry or abandoned due to poor reservoir characteristics or facies variation. The aim of this work is to re-evaluate the reservoir characteristics and facies identification of Sui Main Limestone by using petrophysical analysis and rock physics modeling in the Qadirpur field in the Middle Indus Basin of Pakistan. The reservoir characterization of carbonate rocks is difficult because of their complex pore networking. The well data on five exploratory wells drilled in this gas field are used. The log-derived porosity varies in a very large range of 2%–36%, with an average of 14%–34%. The average porosity of the clean carbonate intervals is 10%–14% and thus has the capacity to accumulate hydrocarbon. The high porosity value indicates the presence of micro-fractures in Sui Main Limestone. These micro-fractures and secondary pores are well interconnected and allow the pore fluids to communicate. The secondary porosity is mainly due to the presence of vuggs and fractures in Sui Main Limestone. The volume of shale varies from 11%–38% in the wells. The net pay zones have hydrocarbon saturation in the range of 40%–70%, which is mainly gas. Using wireline log response, the formation is divided into three facies: limestone, shale, and shaly limestone. This comprehensive work may help improve the prediction of the reservoir quality in heterogeneous carbonate reservoirs and optimize field development.

Spreadsheet-based programming has become a worldwide computational tool and a powerful platform for executing scientific calculations in different engineering disciplines. The inherent advantage of spreadsheets exists in integrated storage and the ability to manipulate matrices along with wide-ranging mathematical calculations, plotting, and diagrammatic presentation. This paper presents a user-friendly and interactive spreadsheet program “AVA-anisotropy” to characterize the primary P-wave amplitude versus incident angle (AVA) responses in vertically transverse isotropic (VTI), horizontally transverse isotropic (HTI), and orthorhombic media. The set of Ruger’s equations for isotropic, VTI, HTI, and orthorhombic media are solved to describe the seismic energy partitioning at an anisotropic interface. The spreadsheet program has three main sections: basic concepts, data input, and AVA modeling for anisotropic media. The interactive data input and on-screen mathematical and graphic presentation of the spreadsheet enables the students to have an in-depth examination of the effects of changing input data and the resulting model. This greatly helps them in understanding the energy partitioning in anisotropic medium.

The proper understanding of earthquake geometry and location is very important to understand the seismicity of an area. In the present study, 185 earthquakes that occurred in the northwest Himalaya of magnitude Mw > 0.6 between 2010 and 2013 were relocated using the Modified Joint Hypocenter Determination method. After examining seven velocity models, average VP/VS ~ 1.73 computed by Wadati diagram is used to improve the hypocenter locations of the earthquakes. Based on hypocentral distributions, these earthquakes were classified into four groups. Group 1 is along the Punjal Thrust in Hazara Kashmir Syntaxes. Group 2 belongs to the Indus-Kohistan Seismic Zone whereas group 3 is along the Besham dome and the fourth group is along the Main Mantle Thrust. Shallow crustal earthquakes were relocated to 0–50 km, deep earthquakes were relocated to 50–100 km, and much deep earthquakes were relocated to 250–350 km depth. This analysis will be helpful to understand the seismicity of the northwest Himalaya of Pakistan.

This study describes a method of combining geostatistical analysis with geophysical inversion of 1D electrical resistivity data acquired in the Bannu Basin, northwestern Himalayas of Pakistan. The data has been integrated and broadened from single dimension resistivity data into a 2D model that can be fully visualized and interpreted in a spatial sense. By interpreting and calibrating the electrical resistivity curves with the lithologies and geophysical logs of boreholes, it has been possible to identify unique sedimentary accumulations that occur throughout the basin. Through the use of variogram modelling the spatial extent of these accumulations can be identified and associated with measured hydraulic properties. It has become possible to map the extents and facies of the alluvial systems of the Bannu Basin formed during periods of heightened tectonic activity. The coarser sediments are associated with higher levels of resistivity as measured in the electrical surveys, whereas the finer sediments exhibit characteristically lower resistivities. Thus, the zones of high and low resistivity values become indicative of sediments associated with alluvial fans and lacustrine environments, respectively. The sediments of alluvial fans show relatively low gamma ray levels and higher transmissivities, whereas those of the piedmont deposits as well as lacustrine and sandy plains tend to show medium to high gamma ray values and lower transmissivities. Gross transmissivities were estimated by studying regression relationships between transmissivities measured in boreholes and the apparent formation factors of sediments. These relationships indicate an exponential increase in transmissivity with increasing apparent formation factor. These trends suggest a contrast in transmissivities between alluvial fan and other environments where lacustrine and sandy plains are characterized by low transmissivities. These estimated transmissivities do not represent absolute values but are merely indicative of any high or low trends in transmissivity of sediments, throughout the basin.

The quantification and assessment of groundwater are of great significance for the urbanization and town planning in an area. The current study has been carried out for quantification and assessment of groundwater quality zones by using geo-electrical technique in Faisalabad area (73° 06′ 08″–73° 11′ 59″ E; 31° 35′ 00″–31° 40′ 39″ N) of Pakistan. Vertical electrical soundings (VES) at six locations were conducted by Schlumberger configuration up to 300-m depth of investigation. Modeling technique is used for the interpretation of apparent resistivity, and the true resistivities of various subsurface lithologies were recorded from 2.10 to 55 Ω m for the depth of investigation. Three sand-dominant aquifers were identified at depth intervals of 0–50 m, 50–100 m, and 100–300 m. The VES results are compared and calibrated with the available borehole data taken from the tube wells drilled in the vicinity of the study area. The GIS technique is applied for the preparation of water quality zonation maps. Some of the groundwater quantification parameters such as total volume of the alluvium, total volumes of the water content, and active storage are estimated through GIS applications. Top geo-electrical layer (0–50 m) is dominated by low resistivity zone (10–25 Ω m), having an active storage of 0.71 km3. Intermediate geo-electrical layer (50–100 m) comprised coarse sand with low-to-medium resistivity zone of 10–35 Ω m, showing a low active storage (1.01 km3). Deep geo-electrical layer (100–300 m) is dominant by very low resistivity zone (

This research deals with the sensitivity of the hypsometric integral (HI) and hypsometric analysis to map active sedimentation and tectonics in the southern Suleiman fold and thrust belt (SSFTB)—a part of extensive folds and thrusts system vastly distributed along the western margin of the Indo-Pakistan sub-plate. We used SRTM DEM with 90 m spatial resolution to determine HI values in the SSFTB in Pakistan. In order to estimate maximum, minimum, and mean elevations of the study area, grid of regular squares of different sizes was analyzed. The active erosional stages and topographic development using digital elevation model (DEM)-derived HI were analyzed. The Shuttle Radar Topography Mission (SRTM)-based DEM is employed to carry hypsometric investigation and isobase codings. For the tectonic geomorphological analysis, the HI and hypsometric curves (HCs) were used to decode the recent and active surface deformation and its influence on the local topography of SSFTB. Spatial autocorrelation is applied to compute the distribution of HIs to see the possible clustering, dispersion, or randomization. Spatial autocorrelation demonstrates that the HIs are auto-correlated because of higher positive values of Z-scores. The spatial statistical analyses indicate that the HI clusters and hot spot are spatially correlated with each other having high positive Z-scores. The study concluded that the central parts and north-north-eastern and north-north-western parts of the SSFTB show more hot spots as compared to south-eastern and south-western parts. The analysis reveals that the resolution of the hot spots depends largely on the grid size and its quality decreases with increase in grid size and vice versa. Hot spots corresponding to higher values of HI are steady with uplifting and active topography and reveal a strong connection with the different structures in the study area. Cold spots correspond to the shallow depth earthquakes and active sedimentation close to fault lines.

Mansehra Granitic Complex (MGC) lies in the NW Himalaya of Pakistan. The MGC magmatic rocks are peraluminous, calc-alkaline S-type granitoids. Prior to this study the Mansehra Granite had produced ages of 83 Ma by K/Ar, 215 Ma using Ar/Ar on biotite, and 516 ± 16 Ma, using the whole rock Rb/Sr method. The Susalgali Granite Gneiss, a sheared facies of the Mansehra Granite previously regarded as older than the Mansehra Granite, was dated at 79 Ma using K/Ar on biotite. Hakale Granite, which is intrusive into the Mansehra Granite, had yielded K/Ar muscovite age of 165 Ma. The age of the leucogranites was not reported before this contribution. We have presented the revised geochronology of the MGC magmatic bodies, employing SHRIMP and LA-ICP-MS U-Pb zircon chronometry, to constraint precise crystallization ages and tectonic setting of the NW Himalaya, Pakistan. Dates of emplacement of the Mansehra Granite, leucogranites and Hakale Granite are ca. 478, 475 and 466 Ma, respectively. These new ages are comparable to U-Pb zircon and Rb/Sr dates of other granites and granite gneisses in the Lesser Himalaya to the east, in India, Nepal, south Tibet and SW China. The age components of ca. 1900–1300, 985–920, 880–800 and 690–500 Ma are interpreted as inherited grains. Geochronological and field evidence suggest that the MGC of the NW Himalaya are the product of an Andean-type Cambro-Ordovician accretional orogenesis with continental-continental settings along the northen margin of east Gondwana. On the basis of new age data of the MGC plutonic rocks it is inferred that Cambro-Ordovician accretional event commenced from SW China and extends at least up to NW Pakistan along the northern margin of east Gondwana. However, granitic rocks of Pan African affiliation prevail in central Iran and Turkey along northern and western margins of Gondwana.

Delineation of saline water and freshwater interfaces is a primary objective in groundwater studies and groundwater management. Karak valley, NW Himalaya of Pakistan is situated in a semiarid region where the continuous supply of freshwater is challenging because of high salinity values in groundwater. In this study, vertical electrical resistivity and borehole data are used to mark the freshwater and saline water interfaces. Borehole data collected from different locations in the study area is used to interpret various subsurface lithologies and to calibrate the modeled resistivity curves. The electrical resistivity data indicates that a thick cover of Quaternary sediments is present in the valley. The re-inversion of electrical resistivity data with modern analysis techniques is highly effective to map the boundary between fresh and saline water aquifers in the valley. Inversion technique is applied to generate 2D and 3D subsurface resistivity maps for the delineation of fresh and saltwater surfaces. The presence of saline water aquifer with clay rich sediments is identified by very low resistivity values on the northern part of the valley whereas relatively high resistivity values with sand and gravel sediments on the southeastern part of the valley indicate the presence of freshwater aquifer. The generated 2D resistivity surface maps at different depth levels above and below the water table and formation resistivity distribution map are effectively used to mark the boundary between fresh and saline water zones. The zone of brackish water is clearly seen in the resistivity inverse model at a depth of 5–30 m.

The Khewra Sandstone is widely distributed throughout the Potwar Basin of Pakistan. Its reservoir aspects are evaluated by the interpretation of well log data recorded from Kal-01 and Kal-02 wells in the Kal Oil Field, eastern Potwar Basin. The encountered thickness of the Khewra Sandstone in Kal-01and Kal-02 varies from 60 m to 120 m. On the basis of lithological interpretation from wireline logs the formation is divided into four facies: 1) shale interbedded with minor siltstone and sandstone, 2) sandstone with alternating siltstone and claystone/shale, 3) claystone/shale, siltstone interbedded with fine to medium grained sandstone and 4) fine to coarse grained sandstone with channels. The log derived average porosity in Khewra Sandstone is about 14–22% with permeability ranges from 20–58 mD. Thus, it possesses a large storage capacity for moveable hydrocarbons in Kal Oil Field. Facies 4, in the upper part of the Khewra Sandstone, is interpreted as potential reservoir interval with hydrocarbon saturation ranges from 77–79%. Based on isopach map, the formation is interpreted to be well developed in NE-SW which gradually thins basinward to the west and northwest direction. The play fairway analysis suggested very high chances of hydrocarbon entrapment is in the Kal Oil Field.

The discrimination of hydrocarbon (gas or oil) facies from non-hydrocarbon (wet sands) facies is an important goal in quantitative seismic interpretation and reservoir estimation. The differentiation of hydrocarbon facies from non-hydrocarbon in Mississauga Formation of early Cretaceous in Penobscot area is a difficult task due to smaller net pay thickness and shaly sand intervals. Based on seismic interpretation and wireline logs, five sand plays are identified in the middle of Mississauga Formation. Four sands have hydrocarbons while top of sand 5 represents hydrocarbon water transition zone. Among these four, the pay sand 4 is analyzed for hydrocarbon facies. Wireline logs and seismic data are used to derive various amplitude versus offset (AVO) based attributes such as: acoustic (I P ) and shear (I S ) impedances, Poisson ratio (σ) etc. Further, the combined attributes e.g., product of Lame parameters (μ, λ) with density (ρ), their ratio (λ/μ), difference between bulk modulus (K) and shear modulus (μ), Δμρ/μρ, Δ(λ/μ + 2)(λ/μ + 2) and the pore space modulus (K P ) are also analyzed to find out the best attribute as a hydrocarbon facies discriminator from non-hydrocarbon facies in the shale imbedded pay sand 4 of Mississauga Formation. First, petrophysical parameters such as P and S wave impedances, Lame’s parameters etc. are extracted from log data. Then, appropriate pairs of seismic attributes are crossplotted so that the hydrocarbon and non-hydrocarbon facies cluster together for quick identification and interpretation. Gamma ray index is crossplotted against spontaneous potential log to mark sand and shale facies. Fluid substitution modeling for various fluid types and saturation is also done which demonstrate that the cross-plots between different rock physics parameters can be used to distinguish between reservoir fluids. Our analysis reveals single P-wave based attributes are not sufficient to discriminate fluids thus the use of multi-attributes such as K P , λρ and K-μ is more effective to discriminate the hydrocarbon and non-hydrocarbon facies. The analysis of these cross-plots was done to map the reservoir sands and the hydrocarbon-water contact.

In poroelastic models, the effective compressibility of rock saturating fluid is conventionally taken as the adiabatic compressibility. This compressibility is valid for seismic waves having frequencies large enough to neglect heat exchanges between the rock matrix and the pore fluid, which are subjected to undergo temperature variations in response to seismic wave propagation. For low enough frequencies, heat flows back and forth across the rock/fluid interfaces, which leads the fluid to smaller temperature variations resulting in a higher compressibility than in the absence of the rock. An analysis of the characteristic heat conduction time over the pore and grain lengths shows that the rock-fluid composite should be considered under thermal relaxation in the surface seismic frequency band rather than the conventional high-frequency (unrelaxed) limit. Our analysis for a rock-fluid system shows that in the low-frequency limit, the effective compressibility of the saturating fluid is neither isothermal nor adiabatic but is equal to the average of the adiabatic and isothermal fluid compressibilities weighted by the volumetric heat capacities of the fluid and rock, respectively. The resulting bulk moduli and compressional velocities of fluid-saturated rock are lower than the conventional values. P wave velocity dispersion, in poorly consolidated rocks, is about 15–20 % subject to the type of saturating fluid is rich in acidic gases (CO2, H2S).

International audience; In seismic applications, the bulk modulus of porous media saturated with liquid and gas phases is often estimated using Gassmann's fluid substitution formula, in which the effective bulk modulus of the two-phase fluid is the Reuss average of the gas and liquid bulk moduli. This averaging procedure, referred to as Wood's approximation, holds if the liquid and gas phases are homogeneously distributed within the pore space down to sizes well below the seismic wavelength and if the phase transfer processes between liquid and gas domains induced by the pressure variations of the seismic wave are negligible over the timescale of the wave period. Using existing theoretical results and low-frequency acoustic measurements in bubbly liquids, we argue that the latter assumption of "frozen" phases, valid for large enough frequencies, is likely to fail in the seismic frequency range where lower effective bulk modulus and velocity, together with dispersion and attenuation effects, are expected. We provide a simple method, which extends to reservoir fluids a classical result by Landau and Lifshitz valid for pure fluids, to compute the effective bulk modulus of thermodynamically equilibrated liquid and gas phases. For low gas saturation, this modulus is significantly lower than its Wood's counterpart, especially at the crossing of bubble point conditions. A seismic reflector associated to a phase transition between a monophasic and a two-phase fluid thus will appear. We discuss the consequences of these results for various seismic applications including fizz water discrimination and hydrocarbon reservoir depletion and CO2 geological storage monitoring. © 2013 Saudi Society for Geosciences.

Naturally occurring gas hydrates are potential future energy source. A significant amount of gas hydrates is interpreted through seismic reflection data in the form of bottom simulating reflector (BSR) present in the sediments of the convergent continental margin of Pakistan. However, the seismic character of these hydratebearing unconsolidated sediments is not properly investigated. Since no direct measurements are available for quantitative estimation of gas hydrate and free gas in these sediments, therefore detailed knowledge of seismic velocities is essential. Seismic velocities of the gas hydrate-bearing sediments in the study area are estimated by using the effective medium theory and the fluid substitution modeling. The results show that the presence of gas hydrates increases the stiffness of the unconsolidated sediments; whereas the presence of free gas decreases the stiffness of these sediments. It is noted that seismic velocities and density of hydrate-bearing sediments are highly affected by saturation and distribution pattern of gas hydrates. The hydrate-bearing sediments seem to be characterized not only by high P-wave velocity (about 2800 m/s) but also by anomalously low S-wave velocity (about 850 m/s). As pure gas-hydrates have much higher seismic velocities than those of host sediments, presence of gas-hydrate increases the seismic velocities, whereas free-gas below the hydrate-bearing sediments decreases the velocities. Seismic reflection from the BSR exhibits a wide range of amplitude variation with offset characteristics, which depend upon the saturation and distribution of hydrates above and free gas below the BSR. We have also demonstrated that some attributes like acoustic and shear impedances, and AVO can be used as important proxies to detect gas hydrate saturation.