Identification of effective traps north of Boerjianghaizi Fault, Hangjinqi area, Ordos Basin

The area to north of the Boerjianghaizi Fault is on the northern edge of the tight-gas bearing area in the Upper Paleozoic in the Ordos Basin. A near-source braided river sand body serves as the main reservoir. Sand bodies in this area have low porosity and low permeability, which is nevertheless better than those in the basin. The gas-water differentiation caused by the superposition of a low-permeability channel sand body and a low-amplitude structure complicated trap evaluation and gas-water relationship identification. Through the difference analysis of structure, logging and seismic waveform, a small anticlinal gas reservoir was dissected in Member 1 of Shihezi Formation. The gas-water interface in the trap was made clear and an identification method was proposed. The sand-structural superposition relationship in Member 1 is a wide channel + a small anticline, with small trap area and volume. However, the sand-structural superposition relationship in members 2 and 3 is a narrow channel + a non-closed structure, mostly structural-lithologic composite traps, with a large number of traps and a large trap area. Besides the comprehensive evaluation of sand body, structure, sealing conditions, etc., it is also important to demonstrate the location of the gas-water interface.