Muhammad Kamran Jafri

Reverse ion exchange as a major process controlling the groundwater chemistry in an arid environment: a case study from northwestern Saudi Arabia

Assessment of groundwater quality is of utmost significance in arid regions like Saudi Arabia where the lack of present-day recharge and high evaporation rates coupled with increasing groundwater withdrawal may restrict its usage for domestic or agricultural purposes. In the present study, groundwater samples collected from agricultural farms in Hail (15 samples), Al Jawf (15 samples), and Tabuk (30 samples) regions were analyzed for their major ion concentration. The objective of the study was to determine the groundwater facies, the main hydrochemical process governing the groundwater chemistry, the saturation index with respect to the principal mineral phases, and the suitability of the groundwater for irrigational use. The groundwater samples fall within the Ca–Cl type, mixed Ca–Mg–Cl type, and Na–Cl type. Evaporation and reverse ion exchange appear to be the major processes controlling the groundwater chemistry though reverse ion exchange process is the more dominating factor. The various ionic relationships confirmed the reverse ion exchange process where the Ca and Mg in the aquifer matrix have been replaced by Na at favorable exchange sites. This phenomenon has accounted for the dominance of Ca and Mg ions over Na ion at all the sites. The process of reverse ion exchange was further substantiated by the use of modified Piper diagram (Chadha’s classification) and the chloro-alkaline indices. Evaporation as a result of extreme aridity has resulted in the groundwater being oversaturated with aragonite/calcite and dolomite as revealed by the saturation indices. The groundwater samples were classified as safe (less than 10) in terms of sodium adsorption ratio (SAR) values, good (less than 1.25) in terms of residual sodium carbonate (RSC) values, and safe to moderate (between 0 and 3) in terms of Mg hazard for irrigation purposes. Though the high salinity groundwater in the three regions coupled with low SAR values are good for the soil structure, it can have a negative impact on the crop production by adversely affecting the crop physiology. Cultivation of high-salinity-resistant varieties of crops is recommended for maximum agricultural productivity.

Seismic and well log driven structural and petrophysical analysis of the Lower Goru Formation in the Lower Indus Basin, Pakistan

The Sinjhoro concession is prolific gas-producing block situated on the eastern limb of the Lower Indus Basin in Pakistan. It contains several development and production (D & P) leases, which are producing gas from Cretaceous rocks. The present study aimed to evaluate the structural and petrophysical properties of the Lower Goru Formation using a 2D seismic and well-driven integrated study. A seismic driven time structure map of the Lower Goru Formation was generated, which depicted horst and graben structures oriented predominantly in a NNW-SSE direction. These normal faults are deep seated and potentially provide a vertical primary migration pathway to hydrocarbon flow. A prospective lead of 20 ms was identified in the northwestern portion of the structural map, which could be explored further. Besides this, a RMS amplitude map was generated within the target reservoir level to show the general sand body distribution within the reservoir. Our study revealed that the reservoir quality sands are deposited in the eastern portion of the study area. The identified lead is also located on a fair to good level of sand body which is producing from the well drilled to the south of the prospective area. Additionally, it is strongly recommended to conduct an infill seismic survey over and around the newly identified prospect in order to validate its existence and aerial outspreads. Well correlation, petrophysical data logs (PDLs) and cross-plot techniques were adopted to predict the petrophysical properties of the reservoir level. During the petrophysical study, two prospective zone were identified, with Zone-II showing more promising results for hydrocarbon presence than Zone-I. The present research has shown that integration of seismic attributes with petrophysical calculations can help to identify new prospective leads even in cases where there is less seismic data coverage.

Risk assessment through evaluation of potentially toxic metals in the surface soils of the Qassim area, Central Saudi Arabia

Metal pollution is an increasing environmental problem worldwide, especially in regions undergoing rapid development. The present work highlights the extent of metal pollution in the central part of Saudi Arabia, which is currently experiencing significant agricultural development. The study determined concentrations of Hg, Cd, Zn, As, Mo, Cu, Pb and Cr in surface soils, assessing the level of pollution and potential ecological risks using soil quality guidelines, the geo-accumulation index (Igeo), the Hakanson potential ecological risk index (RI) and standard statistical analysis methods. Overall, the mean potential ecological risk values of metals in the surveyed soils display the following decreasing trend: Hg>Cd>Pb>As>Cu>Zn>Mo>Cr. The potential ecological risks associated with the eight investigated metals in the study area were high for Hg and Cd, and ranged from considerable too low for the rest of the analysed metals. The results also showed that surface soils in the study area are heavily affected by agricultural activities, municipal waste, local industries and quarries. These anthropogenic activities may, therefore, pose a risk to soil and water resources, and have the potential to change the physiochemical characteristics of the associated ecosystem.

Improved reservoir characterisation using fuzzy logic platform: an integrated petrophysical, seismic structural and poststack inversion study

There is a tendency for applying different integrated geophysical approaches for better hydrocarbon reservoir characterisation and interpretation. In this study, petrophysical properties, seismic structural and poststack seismic inversion results are integrated using the fuzzy logic AND operator to characterise the Tensleep Sandstone Formation (TSF) at Powder River Basin (PRB), Wyoming, USA. TSF is deposited in a coastal plain setting during the Pennsylvanian era, and contains cross-bedded sandstone of Aeolian origin as a major lithology with alternative sabkha dolomite/carbonates. Wireline logging datasets from 17 wells are used for the detailed petrophysical evaluation. Three units of the TSF (A-sandstone, B-dolomite and B-sandstone) are targeted and their major rock properties estimated (i.e. shale/clay volume, Vsh; porosity, φEff; permeability, K; fluid saturations, Sw and SH; and bulk volume water, BVW). The B-sandstone zone, with its petrophysical properties of 5–20% effective porosity, 0.10–250 mD permeability and hydrocarbon potential up to 72%, is considered the best reservoir zone among the three studied units. Distributions of the most important petrophysical parameters of the B-sandstone reservoir (Vsh, φEff, K, Sw) are generated as GIS thematic layers. The two-dimensional (2D) and three-dimensional (3D) seismic structural interpretations revealed that the hydrocarbons are entrapped in an anticlinal structure bounded with fault closures at the west of the study area. Poststack acoustic impedance (PSAI) inversion is performed on 3D seismic data to extract the inverted acoustic impedance (AI) cube. Two attribute slices (inverted AI and seismic amplitude) were extracted at the top of the B-sandstone unit as GIS thematic layers. The reservoir properties and inverted seismic attributes were then integrated using fuzzy AND operator. Finally, a fuzzy reservoir quality map was produced, and a prospective reservoir area with best reservoir characteristics is proposed for future exploration. The current study showed that integration of petrophysical, seismic structural and poststack inversion under a fuzzy logic platform can be used as an effective tool for interpreting multiple reservoir zones. In this study, petrophysical properties, seismic structural and poststack seismic inversion results are integrated using the fuzzy logic AND operator to characterise the Tensleep Sandstone Formation at Powder River Basin, Wyoming, USA. The 3D seismic cube and logging datasets of 17 wells are used for enhancing the seismic and petrophysical evaluation.

Evaluation of metals that are potentially toxic to agricultural surface soils, using statistical analysis, in northwestern Saudi Arabia

Abstract Heavy metals in agricultural soils enter the food chain when taken up by plants. The main purpose of this work is to determine metal contamination in agricultural farms in northwestern Saudi Arabia. Fifty surface soil samples were collected from agricultural areas. The study focuses on the geochemical behavior of As, Cd, Co, Cr, Cu, Hg, Pb and Zn, and determines the enrichment factor and geoaccumulation index. Multivariate statistical analysis, including principle component analysis and cluster analysis, is also applied to the acquired data. The study shows considerable variation in the concentrations of the analyzed metals in the studied soil samples. This variation in concentration is attributed to the intensity of agricultural activities and, possibly, to nearby fossil fuel combustion activities, as well as to traffic flows from highways and local roads. Multivariate analysis suggests that As, Cd, Hg and Pb are associated with anthropogenic activities, whereas Co, Cr, Cu and Zn are mainly controlled by geogenic activities. Hg and Pb show the maximum concentration in the analyzed samples as compared to the background concentration.