Main geological features and accumulation models of abnormally high-pressured gas reservoirs in Tarim Basin

The abnormally high-pressured gas reservoirs were well developed in the Tarim Basin. It was discussed in this paper the abnormally high pressures in foreland depressions, including regional evolution, contributing factors, formation of gas-bearing structures, accumulation mechanisms and periods, and then presenting accumulation models for the Kuqa Depression and the Yecheng Sag respectively. The keys for abnormally high-pressured gas reservoirs and the exploration targets were studied. There were 6 abnormally high-pressured gas reservoirs in Kuqa area, 5 of which were late-charged while only the Yinan2 gas reservoir was self-sourced. The main accumulation period was from the Late Miocene to the Early Pliocene. Anticlines were controlled by a group of overstep reverse faults. Natural gas charged into gas-bearing structures directionally due to the structural compression since Pleistocene. Self-sourced high pressure and transitional high pressure together formed abnormally high pressure. The deep Paleogene gas reservoir in the Kekeya anticline of Yecheng Sag, namely, the Kalata'er gas reservoir, accumulated in Miocene and adjusted with stratigraphic folding in Pliocene-Early Pleistocene, which was an abnormally high-pressured gas reservoir of late-adjustment type. The shallow Miocene gas reservoir in the Kekeya anticline was late-charged, with both the source beds (the Carbono-Permian and Jurassic) and the deep Paleogene gas reservoir supporting gases, which should be a later secondary-generated accumulation.