Abstract:

The ultra-deep reservoirs beneath salt in the Kelasu structural belt belong to low porosity and fractured sandstone reservoir.
Tectonic fractures are common in this area and show a complex distribution pattern. These widely distributed tectonic fractures have large influence on single-well production of Kelasu structural belt. At present, research on reservoir fracture in this area is mainly focused on description, characterization, and prediction of fractures. However, due to low resolution of seismic data, limited core data and uncertainties in interpretation of images of well logging, the study of is limited. Only some statistical data such as fracture density and fracture opening are applied in the process of hydrocarbon exploration. Outcrop, core, and well logging data were used. In this study, research on reservoir fracture and combinations of fractures is carried out in this area. It is found that there are primary and secondary cracks. The scale of main cracks is larger than that of the secondary cracks. The primary cracks are generally perpendicular to the strata, and are mostly tension cracks or tension-shear cracks. The secondary cracks are generally associated the main cracks. There are many different contacts between the cracks, mainly in“T”,“λ”,“V”,“y”, and“τ”shapes. According to the distribution of contacts between cracks, four combination modes of reservoir cracks have been established in this area including“parallel mode”,“broom like
mode”,“adjust mode”,“echelon mode”. Together with the tectonic process of the formation of faulted anticline and the difference between crack combinations, three types of genetic regions of crack combination have been identified, i.e., are tectonically transitional region, folding-related area, and fault formation area, corresponding to the first, second, and third category of high yield wells,respectively.

Key words: Kelasu structural belt；fractured low porosity sandstone reservoir；crack；crack combination mode；distribu