The effects of soil sampling volume for determining salt present were investigated in situ. Six 2.2‐m2 plots were hand sprinkled over a 5‐d period with a total of 10 cm of water containing 1000 mg/L of chloride as CaCl2. Soil samples were taken at three locations within each plot at 10‐cm increments to 100 cm and at 20‐cm increments to the 160‐cm depth. Two different samplers, 7.9‐ and 2.1‐cm diameter, were used. The salt concentration was measured on a 2:1 extract. The measurements for the larger samples were less variable than the smaller samples. The coefficient of variability (CV) for the total chloride recovered was 8 and 14% for the large and small samples, respectively. In order to compare favorably to the known amount added, the effective radius of the sampling tool was critical. The CV for the chloride concentration calculated in the soil water ranged from 5 to 54% and 12 to 199% for large and small samples by depth.
Throughout the subsurface of the Arabian Peninsula, the approximately 460ft thick, Devonian Jauf Formation generally consists of well-compacted, low-porosity sandstones and shales, but it also includes friable and highly porous sandstones which form significant gas and condensate reservoir intervals. The mineralogy and pore properties of these reservoir intervals at the Hawiyah field (part of the giant Ghawar structure) were studied by integrating petrographic data with petrophysical measurements of reservoir sandstone samples.The reservoir sandstones are mainly composed of quartz arenites containing small amounts of altered potassium feldspar grains, authigenic illite and chlorite. Based on the pore types, which reflect the habits of the intergranular clays, three reservoir sandstone types have been defined: Type A, characterized by macroporosity; Type B, with microporosity; and Type C, with combined laminations of Types A and B. The dominance of pore-lining clay (as in Type A) or pore-filling clay (as in Type B) is the principal factor controlling the petrophysical properties of the samples. Types A and C sandstones contain macro pores, but irreducible water saturation is high (25 to 45%) compared to clean samples elsewhere, because of the presence of micropores associated with clay. In Type B sandstones the irreducible water saturation is commonly greater than 40% because all the pores spaces are in the microporosity range. The irreducible water saturation in Type B sandstones increases rapidly as porosity decreases. When porosity is less than 10%, the corresponding permeability is 0.2 mD, but no economic production can be expected because water saturation is as high as 100%. In the producing intervals, authigenic clays result in low electrical resistivity due to high water saturation; however, water-free gas is produced.
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