Development modes of Triassic Yanchang Formation Chang 7 Member tight oil in Ordos Basin, NW China

Abstract The Triassic Yanchang Formation Chang7 Member tight oil reservoir in Ordos Basin, featuring complex pore-throat structures, low porosity, low permeability, rich micro-fractures and low pressure coefficient, is difficult to produce by advanced water-flooding from cluster vertical wells with low individual-well producing rate. With Block A as an example, the material balance calculation, numerical simulation and field practical analysis showed that the horizontal well production would increase significantly using volumetric fracturing. But the well pattern of water injection in vertical wells and oil production in horizontal wells has high risk of injection water breakthrough in horizontal wells, and the proportion of water breakthrough wells reached 65%. In contrast, the formation energy decreased in depletion development with horizontal wells, in which the oil production kept stable in early period, but decreased quickly after 12 months, the cumulative decline of oil rate in 4 months amounted to 50.3%. Therefore, a development scheme of depletion production from volumetric fracturing horizontal wells at first and then water-flooding huff and puff after producing energy is deficient was proposed. Following this scheme, the daily oil rate of single well increased by 78.3% after the first cycle of water huff-and-puff than before the treatment, marking the initial success of the measure.