Abstract:

 Typical tight clastic reservoirs were developed in the Lower Permian Fengcheng Formation in Wu-Xia area in the northwestern margin of the Junggar Basin. Based on the geological and geophysical data, the reservoirs′ characteristics have been studied. The results show that the fans are relatively large during the early and late periods of the Fengcheng Formation, with small-scale slump turbidite fans and shoal-bar sand bodies sporadically distributed. The water bodies expanded and the fan bodies were not developed in the middle stage of the Fengcheng Formation. The physical properties of shoal-bar sandstones are better than those of the sandstones of fan delta front and turbidite fans. Glutenites with high maturity are high-quality reservoir rocks. The volcanic materials in the rocks had an impact on the reservoir diagenetic evolution, thereby affecting the reservoir quality. The plastic tuff debris reduced the compressive strength; the tuff debris were exposed to the hydrolysis and alteration during the burial process, precipitating different minerals, which destroyed the porosity; the dissolution of the feldspar, rock debris, matrix and various authigenic minerals increased the porosity to some extent. The clastic reservoirs in the Fengcheng Formation are overall tight sandstones with low porosity and permeability, and the development of “sweet spots” are under the compound control of many factors, including the sedimentary facies, rock components, particle sizes, maturity, and the development of dissolution.

Key words: tight reservoirs, deep reservoirs, clastic rocks, Fengcheng Formation, Junggar Basi