Integrated geophysical interpretation and reservoir characterization of the Ranikot Formation in Mehar Block, Lower Indus Basin, Pakistan

[1] PPL official e-report, Sawan Gas Field. www.ppl.com.pk/content/sawan-gas-field-overview, 2018.[2] M.J. Khan, M. Umar, M. Khan and A. Das, “2D Seismic Interpretation to Understand the Structural Geometry of Cretaceous Sand Packages, Jabo Field, Pakistan”, The Nucleus, vol. 56, pp 78-85, 2019.[3] H.M. Anwer, A.M. Tiago, A. Ali and A. Zubair, “Effects of sand shale anisotropy on amplitude variation with angle (AVA) modelling: the sawan gas filed (Pakistan) as a key study for south Asia’s sedimentary basins”, J. Asian Earth Sci, vol. 147, pp. 516-531, 2017.[4] T.S. Abbas, K. Mirza and J.S. Arif. “Lower Goru Formation-3D Modeling and Petrophysical Interpretation of Sawan Gas Field, Lower Indus Basin, Pakistan”, The Nucleus, vol. 52, pp.138-145, 2015.[5] S.M. Siyar, M. Waqas, S. Mehmood, A. Jan, M. Awais and F. Islam, “Petrophysical characteristics of Lower Goru Formation (Cretaceous) in Sawan gas field, Central Indus basin, Pakistan”. J. Biodiv. Envir. Sci., vol. 10, pp. 260-266, 2017.[6] N. Ahmad and M.R. Khan, “Evaluation of a Distinct Sub-Play for Enhanced Exploration in an Emerging Petroleum Province, Bannu-Kohat Sub-Basin, Pakistan”. AAPG Int. Conf. and Ex., Milan, Italy, October 23-26, 2011.[7] M.J. Khan, M. Ali and M. Khan, “Gamma ray-based facies modelling of lower Goru formation: a case study in Hakeem Daho well lower Indus basin Pakistan”, Bahria Univ. Res. J. Earth Sci., vol. 2, pp. 40-45, 2017.[8] M.O. Baig, N.B. Harris, H. Ahmed and M.O.A. Baig, “Controls on reservoir diagenesis in the Lower Goru Sandstone Formation, Lower Indus basin, Pakistan”, J. Pet. Geol., vol. 39, pp. 29–47, 2016.[9] A. Berger, S. Gier and P. Kroi, “Porosity-preserving chlorite cements in shallow marine volcanoclastic sandstones; evidence of the Sawan gas field Pakistan”. AAPG Bull., vol. 93, pp. 595-615, 2009.[10] N. Ahmed, P. Fink, S. Sturrock, T. Mahmood and M. Ibrahim, “Sequence stratigraphy as predictive tool in lower Goru fairway, lower and middle Indus platform, Pakistan”, Pak. Assoc. Petro. Geoscientist, Annual Tech. Conf., pp. 85-104, 2004.[11] U.B. Nisar, S. Khan, M.R. Khan, A. Shahzad, M. Farooq and S.A.A. Bukhari, “Structural and reservoir interpretation of Cretaceous lower Goru formation, Sanghar area, Lower Indus basin, Pakistan”, J. Himalaya Earth Sci., vol. 49, pp. 41-49, 2016.[12] I.B. Kadri, “Petroleum geology of Pakistan”, Pakistan Petroleum Limited, Karachi, 1995.[13] T. Azeem, Y.W. Chun, P. Khalid, I.M. Ehsan, F. Rehman and A.A. Naseem, “Sweetness analysis of Lower Goru sandstone intervals of the Cretaceous age, Sawan gas field, Pakistan”, Episodes: J. Int. GeoSci., vol. 41, pp. 235-247, 2018.[14] C.J. Wandrey, B.E Law and H.A. Shah. “Sembar Goru/Ghazij composite total petroleum system Indus and Sulaiman-Kirthar geologic Provinces Pakistan and India”, US Geolog. Survey, USA, 2004.[15] M. Naeem, M.K. Jafri, S.S. Moustafa, N.S. AL-Arifi, S. Asim, F. Khan and N. Ahmed, “Seismic and well log driven structural and petro-physical analysis of the Lower Goru Formation in the Lower Indus Basin, Pakistan”, Geosci. J., vol. 20, pp. 57–75, 2016.[16] A. Nazeer, S.A. Abbasi and S.H. Solangi, “Sedimentary facies interpretation of Gamma Ray (GR) log as basic well logs in Central and Lower Indus Basin of Pakistan”, Geodesy Geodyn. 7, pp. 432-443, 2016.[17] N. Ahmad and S. Chaudhry, “Kadanwari gas field, Pakistan: a disappointment turns into an attractive development opportunity”, Petrol. Geosci., vol.8, pp. 307–316, 2002.[18] J.J. Chow, L. Ming-Ching and S. Fuh, “Geophysical well log study on the paleoenvironment of the hydrocarbon producing zones in the Erchungchi Formation, Hsinyin, SW Taiwan”, Terr. Atmos Ocean Sci., vol. 16, pp. 531-543, 2005.[19] M. Ali, M.J. Khan, M. Ali and S. Iftikhar, “Petrophysical Analysis of Well Logs for Reservoir Evaluation: A Case Study of ‘Kadanwari’ Gas Field, Middle Indus Basin, Pakistan”, Arabian J. Geosci. vol. 12, 2019.[20] I.A.K. Jadoon, R.D. Lawrence and R.J. Lillie, “Seismic data, geometry, evolution, and shortening in the active Sulaiman Fold-and-Thrust Belt of Pakistan, Southwest of the Himalayas”, AAPG Bull., vol. 78, pp. 758–774, 1994.[21] S.H. Solangi, A. Nazeer, S.A. Abbasi, L.D. Napar, P.A. Usmani and A.G. Sahito, “Sedimentology and petrographic study of B-sand of Upper sands of Lower Goru Formation, based well cuttings and wire line logs from wells of southern Sindh monocline, lower Indus basin, Pakistan”, Bahria Uni Res. J. Earth Sci. vol. 1, pp 45-54, 2016.[22] G. Asquith and C. Gibson, “Basic well log analysis for geologists”, AAPG methods in exploration series, Tulsa, pp. 2l6, 1983. [23] F.J. Lucia, “Rock-fabric/petrophysical classification of carbonate pore space for reservoir characterization”, AAPG bulletin, vol. 79, pp. 1275-1300, 1995.[24] M.H. Rider, “Geologic interpretation of well logs”, Whittles Publishing Services, 1999.

Riparian buffers and stream channel widths along river networks have extremely significant ecological influences on parameters and stressors associated with riparian health indicators (RHIs). It is imperative for countries that rely heavily on rivers for irrigation to protect RHIs such as habitat, plant cover, regeneration, exotics, and erosion. It is unclear which protection methods are most effective for RHIs in less developed countries, such as Pakistan. This study fills this gap by using a quick field-based technique that includes 273 transects and examines the response of RHIs in the upper and lower Indus River basins (IRB). In the lower Indus basin (LIB), riparian buffer and stream channel widths had the most considerable influence on RHIs using Pearson’s correlations, ranging from ̶ 0.47 < r < 0.71 and ̶ 0.41 < r < 0.32, respectively. There was a significant relationship between stressors and RHIs in the LIB when these widths were changed, and stressors had a significant influence on habitat ̶ 0.37 < r < 0.41, plant cover ̶ 0.32 < r < 0.38, regeneration ̶ 0.29 < r < 0.25, erosion ̶ 0.34 < r < 0.49, and exotics ̶ 0.39 < r < 0.24. In contrast, these stressors in the upper Indus basin (UIB) also adversely affected habitat ̶ 0.28 < r < 0.27, plant cover ̶ 0.34 < r < 0.26, regeneration ̶ 0.19 < r < 0.26, erosion ̶ 0.38 < r < 0.23, and exotics ̶ 0.31 < r < 0.30. It was found from the principal component analysis that the responses of RHIs and stressors varied considerably between the UIB and LIB. Additionally, the agglomerative hierarchical cluster analysis of the RHIs and stressor indices revealed dissimilarities in the UIB and LIB. This study supports the need to examine riparian regions along long rivers, which are subject to the same administrative strategies. Large river ecosystems need revised standards to prevent further degradation based on ecological indicators.

The lithospheric velocity structure of the lower Indus basin has been evaluated through inversion of fundamental modes of both Love and Rayleigh wave group velocities from the broadband records of a seismic network maintained by the Institute of Seismological Research, Gujarat, India. We have considered three clusters of wave paths A, B, and C that mainly cross the lower Indus basin from south to north; the wave paths of A mainly cross the continental shelf, and the wave paths of B and C pass through the lower Indus basin. The measured group velocities correspond to periods of 5 to 90 s for Rayleigh waves, and 5 to 115 s for Love waves. These data sets resolve the structure of the lithosphere through a nonlinear inversion based on a genetic algorithm with a wide solution space. The mean and standard deviation (S.D.) of the 70 accepted solutions for each of these three clusters provide the 2D structure for the lower Indus basin from south to north. The sediment consists of two layers with total thickness from 5.7 to 6.6 km increasing northward. The crustal thickness also increases northward from 32.9 (cluster A) to 39.7 km (cluster C) in the lower Indus region. The S -wave velocity below the crust varies from 4.55 to 4.59 km/s, which is close to the corresponding velocity of 4.60 km/s of the Indian shield region to the east of the Aravalli range. The thicknesses of the lithosphere, as well as the velocities of the uppermost mantle of the lower Indus plain, are similar to that of the Indian shield.

Abstract. The impact of drought on environmental flow (EF) in 27 catchments of the Indus Basin is studied from 1980–2018 using indicators of hydrologic alterations (IHAs). The standardized precipitation evapotranspiration index (SPEI) was systematically propagated from one catchment to another using principal component analysis (PCA). Threshold regression is used to determine the severity of drought (scenario 1, drought severity that causes low flows) and the month (scenario 2, months where drought has resulted in low flows) that trigger low flows in the Indus Basin. The impact of drought on low EFs is quantified using range of variability analysis (RVA), which is an integrated component of the IHA used to study the hydrological alterations in environmental flow components (EFCs) by comparing the pre- and post-impact periods of human and/or climate interventions in EFCs. The hydrological alteration factor (HAF) is calculated for each catchment in the Indus Basin. The results show that most of the catchments were vulnerable to drought during the periods of 1984 to 1986, 1991/1992, 1997 to 2003, 2007 to 2008, 2012 to 2013, and 2017 to 2018. On a longer timescale (SPEI-12), drought is more severe in the lower Indus Basin (LIB) than in the upper Indus Basin (UIB). The IHA pointed out that drought significantly impacts the distribution of EFCs, particularly extremely low flow (ELF) and low flow (LF). The magnitude and frequency of the ELF and LF events increase as drought severity increases. The threshold regression provided useful insights, indicating that moderate drought can trigger ELF and LF at shorter timescales (SPEI-1 and SPEI-6) in the UIB and middle Indus Basin (MIB). Conversely, severe and extreme droughts trigger ELF and LF at longer timescales (SPEI-12) in the LIB. The threshold regression also divided the entire study period (1980–2018) into different time periods (scenario 2), which is useful for quantifying the impact of drought on low EFs using the SPEI coefficient. Higher SPEI coefficients are observed in the LIB, indicating high alterations in EF due to drought. HAF showed high alterations in EF in most of the catchments throughout the year except in August and September. Overall, this study provided useful insights for analysing the effects of drought on EF, especially during low flows.

<strong class="journal-contentHeaderColor">Abstract.</strong> The impact of drought on environmental flow (EF) in 27 catchments of the Indus basin is studied from 1980&ndash;2018 using the Indicators of Hydrologic Alterations (IHA). The standardized Precipitation Evapotranspiration Index (SPEI) was systematically propagated from one catchment to another using principal component analysis (PCA). Threshold regression is used to determine the severity of drought (scenario-1) and month (scenario-2) that trigger low flows in the Indus Basin. The impact of drought on low EFs is quantified using the Range of variability analysis (RVA). The hydrological alteration factor (HAF) is calculated for each catchment in the Indus basin. The results show that most of the catchments are vulnerable to drought during the periods 1984&ndash;1986, 1991/1992, 1997 to 2003, 2007 to 2008, 2012 to 2013, and 2017 to 2018. On a higher time scale (SPEI-12), drought is more severe in Lower Indus Basin (LIB) than in the Upper Indus Basin (UIB). IHA pointed out that drought significantly impacts the distribution of environmental flow components, particularly extreme low flow (ELF) and low flow (LF). The magnitude and frequency of the ELF and LF events increase as drought severity increases. The threshold regression provided useful insights indicating that moderate drought can trigger ELF and LF at shorter time scales (SPEI-1 and SPEI-6) in the UIB and Middle Indus Basin (MIB). Conversely, severe and extreme drought triggers ELF and LF at higher time scales (SPEI-12) in LIB. The threshold regression also divided the entire study period (1980&ndash;2018) into different time zones (scenario-2), which is useful in quantifying the impact of drought on low EFs using the SPEI coefficient. Higher SPEI coefficients are observed in LIB, indicating high alterations in EF due to drought. HAF showed high alterations in EF in most of the catchments throughout the year except in August and September. The alterations are subject to several factors, including climate change, seasonality of the river flow, land use changes, topography, and anthropogenic activities. Overall, this study provided useful insights for analyzing the effects of drought on EF, especially during low flows.

<strong class="journal-contentHeaderColor">Abstract.</strong> The impact of drought on environmental flow (EF) in 27 catchments of the Indus basin is studied from 1980&ndash;2018 using the Indicators of Hydrologic Alterations (IHA). The standardized Precipitation Evapotranspiration Index (SPEI) was systematically propagated from one catchment to another using principal component analysis (PCA). Threshold regression is used to determine the severity of drought (scenario-1) and month (scenario-2) that trigger low flows in the Indus Basin. The impact of drought on low EFs is quantified using the Range of variability analysis (RVA). The hydrological alteration factor (HAF) is calculated for each catchment in the Indus basin. The results show that most of the catchments are vulnerable to drought during the periods 1984&ndash;1986, 1991/1992, 1997 to 2003, 2007 to 2008, 2012 to 2013, and 2017 to 2018. On a higher time scale (SPEI-12), drought is more severe in Lower Indus Basin (LIB) than in the Upper Indus Basin (UIB). IHA pointed out that drought significantly impacts the distribution of environmental flow components, particularly extreme low flow (ELF) and low flow (LF). The magnitude and frequency of the ELF and LF events increase as drought severity increases. The threshold regression provided useful insights indicating that moderate drought can trigger ELF and LF at shorter time scales (SPEI-1 and SPEI-6) in the UIB and Middle Indus Basin (MIB). Conversely, severe and extreme drought triggers ELF and LF at higher time scales (SPEI-12) in LIB. The threshold regression also divided the entire study period (1980&ndash;2018) into different time zones (scenario-2), which is useful in quantifying the impact of drought on low EFs using the SPEI coefficient. Higher SPEI coefficients are observed in LIB, indicating high alterations in EF due to drought. HAF showed high alterations in EF in most of the catchments throughout the year except in August and September. The alterations are subject to several factors, including climate change, seasonality of the river flow, land use changes, topography, and anthropogenic activities. Overall, this study provided useful insights for analyzing the effects of drought on EF, especially during low flows.

<strong class="journal-contentHeaderColor">Abstract.</strong> The impact of drought on environmental flow (EF) in 27 catchments of the Indus basin is studied from 1980&ndash;2018 using the Indicators of Hydrologic Alterations (IHA). The standardized Precipitation Evapotranspiration Index (SPEI) was systematically propagated from one catchment to another using principal component analysis (PCA). Threshold regression is used to determine the severity of drought (scenario-1) and month (scenario-2) that trigger low flows in the Indus Basin. The impact of drought on low EFs is quantified using the Range of variability analysis (RVA). The hydrological alteration factor (HAF) is calculated for each catchment in the Indus basin. The results show that most of the catchments are vulnerable to drought during the periods 1984&ndash;1986, 1991/1992, 1997 to 2003, 2007 to 2008, 2012 to 2013, and 2017 to 2018. On a higher time scale (SPEI-12), drought is more severe in Lower Indus Basin (LIB) than in the Upper Indus Basin (UIB). IHA pointed out that drought significantly impacts the distribution of environmental flow components, particularly extreme low flow (ELF) and low flow (LF). The magnitude and frequency of the ELF and LF events increase as drought severity increases. The threshold regression provided useful insights indicating that moderate drought can trigger ELF and LF at shorter time scales (SPEI-1 and SPEI-6) in the UIB and Middle Indus Basin (MIB). Conversely, severe and extreme drought triggers ELF and LF at higher time scales (SPEI-12) in LIB. The threshold regression also divided the entire study period (1980&ndash;2018) into different time zones (scenario-2), which is useful in quantifying the impact of drought on low EFs using the SPEI coefficient. Higher SPEI coefficients are observed in LIB, indicating high alterations in EF due to drought. HAF showed high alterations in EF in most of the catchments throughout the year except in August and September. The alterations are subject to several factors, including climate change, seasonality of the river flow, land use changes, topography, and anthropogenic activities. Overall, this study provided useful insights for analyzing the effects of drought on EF, especially during low flows.

ABSTRACTIn previous studies, Patala-Nammal Composite Total Petroleum System (TPS) was recognized as a potential source of hydrocarbon in the Upper Indus Basin, and Sembar-Goru Composite TPS in the Lower Indus Basin. However, petroleum source-rock potential of Cretaceous strata in the Indus Basin is poorly known. In the current study, Rock Eval and total organic carbon (TOC) analyses were conducted to investigate the thermal maturity and source-rock potential of Cretaceous unit in the Lower Indus Basin. The Parh Formation of the Lower Indus Basin is lean in organic contents (TOC < 0.73%) and consistent with immature type-III/IV kerogen. The Upper Goru Formation is fair in organic contents and presents similar characteristics to the Parh Formation with respect to the hydrocarbon generation zone. The Lower Goru Formation presents fair to very good organic contents. The members of Lower Goru Formation have enough organic matter (OM) and are mature, with the exception of Badin shales. The OM, throughout the formation, is predominantly gas prone. The Sembar Formation is fair in organic contents and mature with respect to hydrocarbons generation. These results support that the Lower Goru rocks are comparatively more prospective with respect to hydrocarbons.

A suite of six crude oils from Lower Indus Basin, Pakistan, were analyzed for geochemical characterization of source organic matter (OM) and thermal maturity. Distribution of polycyclic aromatic hydrocarbons (PAHs), alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, and aromatic biomarkers were reported from aromatic fractions of the crude oils. The aromatic hydrocarbons parameters revealed a higher thermal maturity of OM of source rock-generated Lower Indus Basin oils. Calculated vitrinite reflectance values from the methylphenanthrenes index 1 (MPI-1) and methyldibenzothiophene ratio (MDR) indicate that most of the oils reached a late oil generation window of thermal maturity. PAH distributions revealed the oils of two different origins are present in the Lower Indus Basin; two oil samples indicate aquatic source of OM and the aromatic biomarker distributions of retene, 1-MP, and 1,7-DMP indicate a significant contribution of land plant OM in the other four oils. This is the first study to report the distribution of aromatic hydrocarbons from Lower Indus Basin crude oils.

A regional climate modelling system, the Providing REgional Climates for Impacts Studies developed by the Hadley Centre for Climate Prediction and Research, has been used to study future climate change scenarios over Indus basin for the impact assessment. In this paper we have examined the three Quantifying Uncertainty in Model Predictions simulations selected from 17-member perturbed physics ensemble generated using Hadley Centre Coupled Module. The climate projections based on IPCC SRES A1B scenario are analysed over three time slices, near future (2011–2040), middle of the twenty first century (2041–2070), and distant future (2071–2098). The baseline simulation (1961–1990) was evaluated with observed data for seasonal and spatial patterns and biases. The model was able to resolve features on finer spatial scales and depict seasonal variations reasonably well, although there were quantitative biases. The model simulations suggest a non-uniform change in precipitation overall, with an increase in precipitation over the upper Indus basin and decrease over the lower Indus basin, and little change in the border area between the upper and lower Indus basins. A decrease in winter precipitation is projected, particularly over the southern part of the basin. Projections indicate greater warming in the upper than the lower Indus, and greater warming in winter than in the other seasons. The simulations suggest an overall increase in the number of rainy days over the basin, but a decrease in the number of rainy days accompanied by an increase in rainfall intensity in the border area between the upper and lower basins, where the rainfall amount is highest.

Marine sedimentary section across the Paleocene/Eocene (P/E) boundary interval is preserved in the Dungan Formation (Lower Indus Basin), Pakistan. Four dinoflagellate zones in the P/E interval of the Rakhi Nala section (Lower Indus Basin) are identified and correlated. The quantitative analysis of the dinoflagellate cyst assemblages together with geochemical data are used to reconstruct the palaeoenvironment across the P/E interval. The dinocyst assemblages allow the local correlation of the Dungan Formation (part) of the Sulaiman Range with the Patala Formation (part) of the Upper Indus Basin and global correlation of the Zone Pak-DV with the Apectodinium acme Zone of the Northern and Southern hemispheres. The onset of the carbon isotopic excursion (CIE) associated with Paleocene Eocene Thermal Maximum (PETM) is used globally to identify the P/E boundary. The CIE for the total organic carbon (fine fraction) δ13CFF is of a magnitude of −1.7‰ is recorded for the first time in the Indus Basin. The Apectodinium acme precedes and straddles the onset of the CIE in the Indus Basin. This Apectodinium acme is also accompanied by a planktonic and benthonic foraminifera “barren zone.” The CIE in the Indus Basin, coupled with the changes in the dinocyst distribution and the benthonic and planktonic foraminifera assemblages, provides evidence of the changes associated with the PETM in this little-known part of the world. The benthonic foraminiferal assemblage indicates bathyal environment of deposition at the time of P/E boundary interval; the presence of dominantly open marine dinoflagellates and high planktonic foraminiferal ratio suggest that the water column at this site was well connected with the rest of the Tethys.

The uneven hydro-climatic changes and droughts have significantly affected the socioeconomic condition of people dependent on the Indus basin, Pakistan. This study aims to examine the annual and seasonal hydro-climatic trends for the Upper Indus Basin (UIB), Middle Indus Basin (MIB) and Lower Indus Basin (LIB). The mean monthly data from 44 meteorological and 30 hydrological stations have been analyzed. The Mann Kendall test, Spearman’s rho test, linear trend estimation method and Van Belle and Hughes test have been used to perform analysis of hydro-climatic trends. The Standardized Precipitation Index (SPI), Sequential Mann Kendall test and rescaled range analysis have been introduced to detect the seasonal and annual drought. The results showed that significant warming has been observed throughout the Indus basin. The spring precipitation decreased significantly in the UIB with the maximum decrease of 5.3 mm/year. The streamflow of UIB has presented significant increasing trends on annual basis and spring season due to significant warming and glacier melt. The streamflow of MIB presented a significant increase in spring, and it decreased in summer, which can be related to significant warming. The annual precipitation of LIB presented significant increasing trends, and a similar trend has been observed in autumn. However, the LIB showed decreasing streamflow trends on an annual and seasonal basis which is possible due to significant warming trends and water regulation in upstream. The Hurst index value indicates that the Indus basin is expected to maintain current trends and the degree of drought is expected to increase in the future.

Due to the lack of drilling confirmation and the poor imaging quality of the early seismic data in deeper part, there was a great controversy on the understanding of the strata under the Cenozoic in the offshore Indus Basin: some scholars thought that the Deccan volcanic rocks were widely distributed; It is also believed to be Mesozoic sedimentary strata, but its stratigraphic framework, distribution and structural characteristics are not clear. This directly affects the evaluation of exploration potential in this area. Using the latest multi-channel seismic data, we have clearly identified Mesozoic sedimentary strata in the offshore Indus Basin. The offshore Indus basin is composed of the underlying Mesozoic rifting basin and the overlying Cenozoic passive continental margin sedimentary basin. It is a two-stage superimposed basin developed on the stretched and thinned crust of the Indian plate, drifting from the southern hemisphere to the present position together with the Indian continent. Through correlation of sea and land strata, it is found that the Mesozoic offshore Indus Basin is an offshore extension of the lower Indus Basin, and has similar stratigraphic distribution characteristics and structural characteristics to the lower Indus Basin. The correlation of seismic wave sets indicates that the Jurassic, Sembar Formation and Lower Goru Formation of Lower Cretaceous and the Upper Goru Formation of Upper Cretaceous were also deposited in the sea area. The Jurassic and Lower Cretaceous have the stratigraphic characteristics of eastern faulted and western overlapped, and the Upper Cretaceous has the characteristics of east-west double faulted. The basin rifting area expanded westward continuously during the Mesozoic. The Mesozoic strata were controlled by nearly N-S trending faults&amp;#65292;the northern near-shore strata partially reformed by Cenozoic near E-W fault, and the western strata was influenced by the near N-S uplifting and strike-slip structure of Murray Ridge. The average thickness of Mesozoic strata is about 2000m, and the thickest can reach 12000m. The Mesozoic major depocenter is located in the southeast of the basin, the second one is in the northwest. The favorable structural types such as faulted nose, faulted anticline and anticline are mainly developed. These structures were mainly formed during the late Mesozoic compressive uplift period. Therefore, the Mesozoic in the Offshore Indus Basin has the material basis and structural geological conditions for the formation of oil and gas fields. If the favorable structure in Mesozoic can be configured with the depocenter, it will be conducive to hydrocarbon near-source charging. Like the Lower Indus Basin, the Mesozoic is also a favorable direction for petroleum exploration.

Faults can be either conduits or baffles for hydrocarbon flow. Assessing the sealing potential of faults plays a vital role in reducing the risks associated with hydrocarbon exploration. The study area is located in Jherruck Block, Lower Indus Basin, Pakistan. Several intervals within the Lower Goru Formation in Lower Indus Basin are proven hydrocarbon reservoirs. The main aim of the study is to predict the cause of failure of 3 wells (Jherruck B-1, Jamali-1, and Jamali Deep-1), and to propose a new well location based on juxtaposition analysis and shale gouge ratio (SGR). The Upper Sands (sandstone) of the Lower Goru Formation (A-Sand, B-Sand, C-Sand, and D-Sand) have reservoir potential in the region including the Jherruck Block. These reservoir sands have been interpreted in seismic sections to generate time and depth surface maps. Using depth surface maps, Allan diagrams have been constructed for juxtaposition and shale gouge ratio analysis. The integration between juxtaposition and shale gouge ratio analysis suggested that the main reason for the failure of these wells was sandstone to sandstone juxtapositions leading to updip hydrocarbon leakage to the adjacent fault block. In addition to this, the shale gouge ratio indicated low shale gouge distribution in the fault zones. Allan diagram and shale gouge ratio analyses helped us to propose a new well location further northwest of Jherruck B-1 well where sands are juxtaposed against impermeable shale lithology of the Goru Formation and SGR ratio is above 80%.

The depositional signatures of the Cretaceous OAE1a and OAE1b intervals in the Parh Formation, Lower Indus Basin, Pakistan, Eastern Tethys, have been studied to better constrain the Aptian–Albian ocean–climate system. Based on the microfacies attributes, an outer ramp to deep basin is suggested for the deposition of Parh Formation. The quasi-periodic occurrences of radiolarian-rich microfacies and the cyclicity between the outer ramp and deep basin settings throughout the section suggest eutrophication in this part of the Eastern Tethys influenced by Milankovitch cycles. The clastic influx during OAE1a and OAE1b intervals indicate the role of continental runoff in the eutrophication of the basin. The overall negative covariance between radiolarian-rich microfacies and clastic input suggests that upwelling was a major driver of nutrient enrichment rather than continental runoff. The organic enrichment along with pyrite framboids and lack of burrows suggest that dysoxic–anoxic bottom water conditions were common throughout the Aptian and not just in the OAE1a and OAE1b intervals. The poor ventilation of the sea floor was a result of restricted circulation and may have triggered sustained anoxia during Aptian in this part of the Eastern Tethys. Bottom-water currents recharged coarser clastics to the deeper part of the basin during OAE1a and OAE1b intervals. However, the effects of deep ventilated oxic water during the events were reduced by persistent ocean anoxia. Furthermore, the dominance of carbonate sediments throughout the Aptian–lower Albian succession suggests relatively alkaline oceans in this part of Eastern Tethys. A pronounced sea-level rise, as suggested elsewhere was not observed during OAE1a and OAE1b intervals in this part of the Tethys. KEY POINTS The Aptian–Albian hemipelagic sequence of the Parh Formation, Lower Indus Basin, Pakistan, Eastern Tethys has been deposited in an outer ramp to deep basin environment. The quasi-periodic occurrences of radiolarian-rich microfacies and cyclic alternation of depositional environments suggest eutrophication of the basin influenced by Milankovitch cycles. Organic enrichment, pyrite framboids and lack of burrows suggest dysoxic–anoxic bottom-water conditions throughout the Aptian to early Albian.