关键词: 鄂尔多斯盆地, 致密砂岩, 储层特征, 低产原因, 单井产量, 对策

Abstract: Several analytical methods, including casting thin sections, constant-rate mercury intrusion, high-pressure mercury intrusion, low-temperature liquid nitrogen adsorption, stress sensitivity, and water locking damage, were used to investigate the microscopic pore structures and causes for low production of tight sandstone gas reservoirs in the 8^th member of Shihezi Formation, Permian, Upper Paleozoic ("He 8^th member"), Ordos Basin. Then, a solution based on geology-engineering integration was proposed for increasing single-well production. The study shows that the He 8^th member tight sandstone reservoir comprises secondary dissolved pores such as lithic dissolved pores and intercrystal pores, without fractures, indicative of a single-porosity reservoir. The peak throat radius is 0.2-2.2 μm. The pore volume communicated by nearly nano-throats in the reservoir with permeability less than 1 mD is greater than 38%, suggesting as micro-throat reservoir where the micro-throats control the permeability. Under the action of stress, micro-throats are prone to shrinking, closing and quickly absorbing when exposing to water, so that they are stress-sensitive and likely induce water locking damage. In addition, the single sand body is small in scale and low in abundance, so the single-well production is generally low. The solution based on geology-engineering integration for increasing single-well production mainly involves four aspects. First, geologic sweet spots with rich gas and engineering sweet spots in fracturable reservoirs are preferred for development with lower cost and higher efficiency. Second, a specific and customized stimulation program is designed depending on the reservoir characteristics. Third, volume fracturing is applied to increase the stimulated reservoir volume (SRV) through changing the single-porosity reservoir to a dual-porosity (pore-fracture) reservoir and weakening the control of micro-throats on the permeability. Horizontal wells are preferentially deployed along primary channels with ideal vertical connectivity to expand the drainage area. Fourth, multi-layer/zone commingled production is adopted to enhance the single-well productivity.

Key words: Ordos Basin, tight sandstone, reservoir characteristics, causes for low production, single-well production, solution