Classification and Evaluation of Ultra-Low Permeability Reservoirs in the Changqing Oilfield

With the rapid development of the world economy, the exploration and development of unconventional oil and gas resources have become a new hot spot. As an important subset of unconventional reservoirs, ultra-low permeability (ULP) reservoirs have been greatly concerned. Studies suggest that the ultra-low permeability reservoir belongs to the typical tight reservoir. The current low-permeability reservoir classification criteria available in the literature cannot meet the actual needs of ultralow permeability reservoir development. Through researches, reservoir characterization parameters of effective porosity, mainstream throat radius, movable fluid saturation and starting pressure gradient are screened out to build quaternary classification coefficient. A new standard of classification and evaluation of ultra-low permeability reservoirs is established, and ultra-low permeability reservoirs are divided into three categories. Thus it provides a theoretical basis for speeding up the effective development of ultra-low permeability reservoirs. Keywords: unconventional oil and gas; tight oil; ultra-low permeability reservoir; characterization parameter; classification and evaluation Since the beginning of the 21st century, the world economy has entered a new cycle of development. The demand for oil and gas resources in the countries soared. Facing the huge demand for energy, productivity construction and production rate are relatively insufficient throughout the world. Unconventional oil and gas resources are beginning to receive more attention. Ultra-low permeability reservoirs, as important unconventional oil and gas reservoirs, have huge potential for exploration and development, but the current classification of reservoir evaluation criteria cannot meet the needs of ultra-low permeability reservoir exploration and development. In order to effectively guide the exploration and development practice of ultra-low permeability reservoirs, it is of great significance to launch researches on ultra-low permeability reservoir characterization parameter system, and to establish a new classification and evaluation criteria.