AVO-derived attributes to differentiate reservoir facies from non-reservoirs facies and fluid discrimination in Penobscot area, Nova Scotia

Perveiz Khalid,Nisar Ahmed,Khalid Amin Khan,Mustansar Naeem 한국지질과학협의회 2015 Geosciences Journal Vol.19 No.3

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 (IP) and shear (IS) impedances, Poisson ratio (σ) etc. Further, the combined attributes e.g., product of Lamé 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 (ΚP) 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, Lamé’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 KP, λρ and Κ-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.

Petrophysical analysis of a clastic reservoir rock: a case study of the Early Cambrian Khewra Sandstone, Potwar Basin, Pakistan

Shahid Ghazi,Perveiz Khalid,Tahir Aziz,Zulqarnain Sajid,Tanzila Hanif 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.1

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.

An application of variogram modelling for electrical resistivity soundings to characterize depositional system and hydrogeology of Bannu Basin, Pakistan

Asam Farid,Perveiz Khalid,Khan Zaib Jadoon,Muhammad Asim Iqbal,James Small 한국지질과학협의회 2017 Geosciences Journal Vol.21 No.5

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.

An application of rock physics modeling to quantify the seismic response of gas hydrate-bearing sediments in Makran accretionary prism, offshore, Pakistan

Muhammed Irfan Ehsan,Nisar Ahmed,Perveiz Khalid,Liu Xue Wei,Mustansar Naeem 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.3

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.

U-Pb zircon systematics of the Mansehra Granitic Complex: implications on the early Paleozoic orogenesis in NW Himalaya of Pakistan

Mustansar Naeem,Jean-Pierre Burg,Nasir Ahmad,Muhammed Nawaz Chaudhry,Perveiz Khalid 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.4

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.