In situ Raman analysis on the segregated near-equilibrium carbonate-fluid interaction at elevated temperatures (room temperature−260 °C) and pressures (13-812 MPa) in a hydrothermal diamond anvil cell (HDAC) reveals the preservation mechanism of porosity in deep carbonate reservoirs in the northeastern Sichuan Basin. The carbonate-fluid interaction was investigated by separately heating carbonate minerals and rocks with four different acid solutions (saturated CO2 and H2S solutions, HCl, CH3COOH) in a sealed sample chamber. A minor continuous precipitation with increasing temperatures and pressures was observed during the experiments which caused minor sample volume change. The closed system is a preservation of pores and burial dissolution may not be the dominant diagenesis in the origin of porosity. Thin section photomicrographs observations in Changxing and Feixianguan Formations demonstrate that eogenetic pores such as moldic or intragranular pores with late small euhedral minerals, intergranular, intercrystal and biological cavity pores are the main pore types for the reservoirs. Early fast deep burial makes the porous carbonate sediments get into the closed system as soon as possible and preserves the pores created in the early diagenetic stage to make significant contribution to the deep reservoir quality. The anomalous high porosity at a given depth may come from the inheritance of primary pores and eogenetic porosity is fundamental to carbonate reservoir development. The favorable factors for deep reservoir origin include durable meteoric leaching, early fast deep burial, early dolomitization, etc. This deep pores preservation mechanism may be of great importance to the further exploration in deep carbonate reservoirs in the northeastern Sichuan Basin.

The high-pressure phase transition of Mg2Si was investigated using angel dispersive synchrotron radiation X-ray diffraction with diamond anvil cell. A phase transition of Mg2Si occurs from the anti-fluorite structure to a monoclinic structure instead of the anti-cotunnite structure at about 11.1 GPa, which is reversible. Isothermal pressure-volume relationship of anti-fluorite Mg2Si is well described by the third-order Birch–Murnaghan equation of state with V0=64.0(2) Å3 and B0=58(2) GPa.Highlights► Two rounds of angle dispersive XRD experiments, one with laser-heating. ► New monoclinic high-pressure phase of Mg2Si, instead of anti-cotunnite phase. ► EoS parameters of anti-fluorite phase was fitted.

The (Ca1–2xNaxLax)TiO3 (0⩽x⩽0.50⩽x⩽0.5) A-site substituted perovskite compounds have been synthesized and characterized by XRD and Raman spectroscopy at room temperature. The XRD powder diffraction study suggests that the end-member Na1/2La1/2TiO3 crystallizes in the tetragonal space group I4/mcm. The phase transition from Pbnm to I4/mcm   is located between x=0.34x=0.34 and 0.390.39 and is driven by the variation of ionic radii at the A-site. The observed Raman modes are in agreement with group theory analysis, and the relationships between the behavior of structural parameters (e.g. Ti–O–Ti bond angle), indicated by long-range order, and the corresponding Raman frequency shifts and intensity evolution, indicated by short-range order, are established and discussed in terms of the radius effect and the mass effect.X-ray diffraction data and calculated pattern for Na1/2La1/2TiO3, the end-member of the Ca1–2xNaxLaxTiO3 (x=0.5x=0.5). The experimental data are shown as crosses, the calculated fits and difference curves as solid lines. Tick marks (upper row for internal standard silicon) indicate the calculated positions of peaks.

The high-pressure phase transition of Mg2Si was investigated using angel dispersive synchrotron radiation X-ray diffraction with diamond anvil cell. A phase transition of Mg2Si occurs from the anti-fluorite structure to a monoclinic structure instead of the anti-cotunnite structure at about 11.1 GPa, which is reversible. Isothermal pressure-volume relationship of anti-fluorite Mg2Si is well described by the third-order Birch–Murnaghan equation of state with V0=64.0(2) Å3 and B0=58(2) GPa.Highlights► Two rounds of angle dispersive XRD experiments, one with laser-heating. ► New monoclinic high-pressure phase of Mg2Si, instead of anti-cotunnite phase. ► EoS parameters of anti-fluorite phase was fitted.