Mineralogical, Pore and Petrophysical Characteristics of the Devonian Jauf Sandstone Reservoir, Hawiyah Field, Eastern Saudi Arabia

Abstract

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.

Multi-salinity core flooding study in clay-bearing sandstones, a contribution to geothermal reservoir characterisation

“…This experimental core flooding study supports the Waxman-Smits model for fully water-saturated cores, showing the impact of clay in the low salinity range for three tight sandstones with different primary clay mineral presence: kaolinite (A), chlorite (B), and glauconite (C). Saner and Kissami (2003) conducted a similar core flooding test with NaCl brines from 250 000 to 1000 ppm in cores containing 90 % to 95 % quartz with a permeability range from 19.2 to > 1000 mD, finding no shaliness (clayey) effect. Orr et al (2005) developed a partially brine-saturated core flooding test using brines from 150 000 to 60 000 ppm, called CtCw plots, in synthetic samples with different low-clay minerals, detecting the clay effect only in the low brine range for chlorite (8 % v/v), illite (5 % v/v), and montmorillonite (3 % v/v-10 % v/v) but not for kaolinite (5 % v/v).…”

Compositions and Interior Structures of the Large Moons of Uranus and Implications for Future Spacecraft Observations

“…Experimental work by Archie (1942) led to the inference that F is proportional to the porosity Φ to an exponent m called the cementation index: F = Φ − m . The value of the cementation index depends on permeability and is a function of pore shape and tortuosity (e.g., Saner & Kissami, 2003). In an ideal situation where the flow of brines in the rock is unhindered, m tends toward 1.…”

Compositions and Interior Structures of the Large Moons of Uranus and Implications for Future Spacecraft Observations

“…For a porosity of 0.3 and a brine EC of up to 30 S/m at 100 o C (e.g., Ucok et al 1980), we find an effective EC of brine-filled porous rock between 2.5 S/m and 8 S/m. This range is derived from empirical observations by Saner and Kissami (2003) who have measured the macroscopic conductivity as a function of the brine conductivity for a wide range of rock and porosity configurations. It reflects in particular the permeability of the samples: higher permeability leads to higher EC values.…”