Study on sedimentary fades of the middle oil group of the Triassic in Akekule area of Tarim Basin

It is held that the sedimentary fades in oil group mainly include braided stream, lacustrine, sublacustrine fan and delta according to the comprehensive analysis of core observation and the test data of rock, mineral and grain size. There are mainly braided stream and sublacustrine fan in the main sandbody of the oil group, and the sublacustrine fan facies is found for the first time in studied area. The sublacustrine fan can be divided into two subfacies: mid-fan and fan-edge. The braided channel is the main mircrofacies of mid-fan. Natural levee mircrofacies don't present. There are shore-shallow lacustrine and half-deep-deep lacustrine subfacies in the lacustrine facies. Delta facies presents in the sand-mudstone layer at the upper of the main sandbody, and it presents only a part of wells because of the erosion of upper oil group to middle oil group. So the delta facies couldn't form favorable reservoir in the studied area. From north to south, the sedimentary facies of the middle oil group are braided stream-slope shore-shallow lacustrine-half-deep lacustrine (canyon)-sublacustrine fan-deep lacustrine.