ABSTRACT
The Permian Fengcheng Formation in the Mahu Sag was deposited in a volcanic-alkaline lacustrine evaporative environment and contains a unique variety of fine-grained sediments. This study examines, at a millimeter-scale, the influence of sedimentary microfacies on variability of lamina quality in fine-grained sediments in the second member of the Fengcheng Formation (P1f2). The methods used include thin-section identification, X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), nitrogen adsorption, and nuclear magnetic resonance (NMR). Six types of lamina were identified in two different lithofacies: fan-delta front facies (FDFF) and semideep/deep lacustrine facies (SDDLF). The laminae in FDFF are predominantly feldspar-quartz laminae (FQL), reedmergnerite laminae (RL), shortite laminae (SL), alkaline mineral laminae (AML), and chert laminae (CL). The laminae in SDDLF are predominantly FQL, RL, SL, CL, and dolomite laminae (DOL). Variations in reservoir quality, oil-bearing properties, and the fracability of laminae in different sedimentary facies are determined by the combined effects of lamina density, mineral composition, rock structure, organic matter abundance, and microfractures. Analysis of these factors indicates superior reservoir qualities in FDFF. In SDDLF, the pore structure is limited by high lamina density, chert content, and fine grain size with the NMR porosities of FQL, RL, SL, and CL being 1.32, 0.18, 0.84, and 0.39%, respectively. However, in FDFF, the combination of high organic matter content, feldspar, pyrite, and clay minerals has a superior effect on the organic matter and minerals deposited resulting in better pore structure and more storage space for shale oil. The NMR porosities of FQL, RL, SL, and CL are 2.81, 2.53, 1.80, and 1.12%, respectively. Overall, analysis of lamina variations and their relationships with sedimentary facies indicates that the reservoir in FDFF may offer more favorable targets for "sweet spot" evaluation.
ABSTRACT
In this work, a nanoporous template with a controllable channel diameter was used to simulate the oil storage ability of shale pore throats. On the basis of the wetting behaviours at the nanoscale solid-liquid interfaces, the seepage of oil in nano-channels of different diameters was examined to accurately and systematically determine the effect of the pore diameter on the oil storage capacity. The results indicated that the lower threshold for oil storage was a pore throat of 20 nm, under certain conditions. This proposed pore size threshold provides novel, evidence-based criteria for estimating the geological reserves, recoverable reserves and economically recoverable reserves of shale oil. This new understanding of shale oil processes could revolutionize the related industries.
ABSTRACT
Measurement of thermal conductivity of rocks is important to understand the thermal properties of earth materials, the characteristics of terrestrial heat flow, and the formation of oil. In this paper we report thermal conductivity, thermal diffusivity, and heat capacity data for 12 conglomerate, sandstone, and gypsum-bearing samples from the Paleogene Kuqa River profile in Kuqa, China. Samples were measured via the hot disk technique, yielding thermal conductivity values of 0.436 to 0.998 W/mK, thermal diffusivity measurements of 0.395 to 1.314 mm(2)/s, and heat capacity values of 0.439 to 1.717 MJ/m(3)K. These analyses reveal that gypsum-bearing rocks, with their low thermal conductivity, can act as excellent insulators over oil and gas reservoirs, aiding the formation and thermal maturation of petroleum.