Fracture identification and characterization of Ordovician carbonate rock reservoir in block B of the Tahe oilfield

Abstract

The distribution of fractures in fractured-vuggy reservoirs of Ordovician carbonate rock in the Tahe oilfield is one of the main controlling factors for oil and gas enrichment in this area. Determining the spatial distribution of fractures is the key to stable production in this area. First, this article uses cores and thin sections to analyse the characteristics of fractures. The area is dominated by structural fractures, with relatively few dissolution fractures and diagenetic fractures. The average length of the fractures is 5.25 cm, the average opening is 0.21 cm, the average angle is 40.33°, and the average line density is 3.05 lines/m. Second, rock mechanical parameters were calculated using dipole shear wave logging curves and conventional logging curves, and fracture development index (FI) curves were constructed. Using the variations in the performance characteristics of the FI curve the spatial distribution patterns of fractures in different fracture development segments are qualitatively analyse. The predicted results are then verified by combining core, thin section, and imaging logging data, and the coincidence rate reached 83%. The following conclusions are drawn: Vertically, fractures are mostly concentrated in the Yijianfang Formation, with the characteristics of “small scale and scattered”. On the plane, the development scale of fractures in the denudation area is good, with great development potential. Combined with the production of each well, it is verified that the fracture development segment identified by the fracture FI curve has guiding significance for oil and gas exploration.