Application of Stepwise Phase-Controlled Inversion in Deep and Thin Gas Reservoirs of Qingyang Gas Field

The CT3 area in the east of Qingyang Gas field in Ordos Basin is located in a high structural position and has several rows of nose-like structures, which is a favorable area for reservoir accumulation. The main reservoir is H8 gas reservoir in Upper Paleozoic, featuring single layer, thin thickness, deep burial and blurry physical property. It is in urgent need of seismic technique to predict favorable reservoir area. Deterministic inversion has high reliability in describing spatial distribution of reservoir, but its vertical resolution is low, so it cannot quantitatively predict the single sand with an average thickness of only 6m in CT3 area. Geostatistical inversion has high vertical resolution, but is greatly affected by the model and high-frequency randomness. In this paper, the fluid substitution technique for H8 member in the study area will be used for the first time to determine reservoir-sensitive parameters. Combined with the actual geological characteristics, the stepwise phase-controlled inversion is innovated, including modeling constrained by paleogeomorphology and simultaneous inversion constrained by spatial distribution of lithofacies. The inversion results are highly consistent with not only the channel morphology before the deposition of H8 member, but also the actual drilling condition, which indicates the enrichment area in CT3 area. The stepwise phase-controlled inversion process improves the quantitative accuracy of effective reservoirs in deep, thin and tight gas reservoirs, and provides an effective new method for thin reservoir prediction of the same type of oil and gas reservoirs controlled by ancient landform.