Single-well fracture prediction based on R/S-FD numerical analysis method: a case study of Ordovician carbonate reservoir in Tahe Oilfield, Tarim Basin

Fracture is a key factor for high and stable reservoir production in Ordovician carbonatite fracture-cavity reservoirs in the Tahe Oilfield. In this paper, we firstly identify and statistically analyse the medium to small scale fractures in the Ordovician carbonate reservoirs of the Tarim Basin Tahe Oilfield by using a large amount of thin section, core, and imaging logging data. Secondly, the R/S-FD numerical analysis method is introduced to realize the calculation of fracture development segments based on different conventional logging curves, and then the cumulative multiplication method is used to realize the quantitative prediction of fracture development segments in a single well under the constraints of multiple curves. Finally, the fracture identified by the core and FMI imaging logging data was verified with the prediction results of the R/S-FD numerical analysis method to determine the applicability and accuracy of the method in fracture prediction. The results show that Structural fractures predominate in the study area, where high angle, shear fractures are mainly developed; Of the different types of conventional logging curves, the AC, RS and RD curves are highly sensitive and similar to the fracture development segments in carbonate reservoirs. Although GR is sensitive to fractures, it is too different from the rest of the curves to be applied in the comprehensive analysis. DEN and CAL curves are relatively weak in terms of fracture sensitivity and are not suitable to be applied in fracture prediction. The results of R/S-FD fracture identification for different curves show that the method is effective in identifying single, high-angle fractures and multiple, medium-angle fractures, and is inadequate in identifying low-angle and horizontal fractures. Comparison and validation of the R/S-FD fracture identification curves with cores and imaging logs show that the comprehensive fracture identification probability of the method can reach 71.6%, which proves that the method has a strong ability to identify single-well tectonic fractures in carbonate reservoirs. The application of this method to fracture prediction in Ordovician carbonate reservoirs is of great significance for the evaluation of fractured carbonate reservoirs in oil and gas exploration.