File:BLTN12220fig5.jpg

Photomicrographs of calcite types and their fluid inclusions in the Feixianguan Formation. (A) Pre-TSR calcite (yellow arrow) with bitumen filling the microfracture in calcite (blue arrows), implying that the calcite formed before the formation of fracture and oil charging, well LJ1, 3470.40 m (11,382.91 ft). (B) Two-phase aqueous fluid inclusions (yellow arrows) present in pre-TSR calcite, well LJ1, 3470.40 m (11,382.91 ft). Note that no petroleum inclusions were found in pre-TSR calcite. (C) Oil-stage TSR calcite (yellow arrow) with bitumen and oil inclusions, well LJ6, 3936.00 m (12,910.08 ft). (D) Two-phase aqueous fluid inclusions (yellow arrow), bitumen, and oil inclusions (red arrows) are commonly present within the calcite, implying that the calcite formed during the time that oil reacted with anhydrite, well LJ6, 3936.00 m (12,910.08 ft). (E) Gas-stage TSR calcite (yellow arrow), with no evidence of bitumen or oil inclusions found in this type of calcite, suggesting that calcite was formed by gas reacting with anhydrite, well D4, 4793.00 m (15,721.04 ft). (F) Two-phase aqueous fluid inclusions (yellow arrows) commonly present in calcite. Note that no petroleum inclusions were found in gas-stage TSR calcite, well D4, 4793.00 m (15,721.04 ft). From Thermochemical sulfate reduction and fluid evolution of the Lower Triassic Feixianguan Formation sour gas reservoirs, northeast Sichuan Basin, China by Lei Jiang, Richard H. Worden, and Chun Fang Cai, DOI: DOI: 10.1306/10171312220.