Types and distribution of the braided channel reservoir sandstones in the Karamay Formation in Quadrant 1 of the Karamay Oil Field, Xinjiang

The integration of outcrop measurement, core observation and well logs show that the braided channel deposits were developed during the deposition of the S₇, S₅ and S₄ sandstone measures in the Karamay Formation in Quadrant 1 of the Karamay Oil Field, Xinjiang, and may be classified into three types of proximal gravelly braided channel deposits, distal gravelly braided channel deposits and sandy braided channel deposits. Lithologically, the proximal gravelly braided channel deposits are mainly made up of conglomerates, with subordinate sandstones, and have medium-sized porosity and low permeability. A single channel has the sedimentary thickness varying from 2 to 4.5 m and a width from 500 to 800 m, and displays the distribution patterns as the channel-channel associations. The distal gravelly braided channel deposits are the same as the proximal gravelly braided channel in lithology. A single channel has the sedimentary thickness varying from 1.5 to 4 m and a width from 400 to 750 m, and constitutes the distribution patterns as the channel-overbank-channel associations. The sandy braided channel deposits are dominated by the sandstones and occur as medium-sized porosity and low-permeability reservoirs. A single channel has the sedimentary thickness varying from 0.5 to 2.5 m and a width from 300 to 700 m, and constitutes the distribution patterns as the banded or interbanded associations. The positive aspects of the gravelly braided channel sandstones are relatively thick reservoir sections, extensive and well-connected sandstone reservoirs, and thus may be considered as the main target for the petroleum exploration throughout the study area.