A Novel Method for Predicting Drilling Lost Circulation Risk in Fractured Formations Based on the Integration of Well Logging and Seismic Data

Due to the complex geological structures of fractured formations, drilling operations often encounter a narrow safe mud density window, leading to frequent and severe lost circulation events. This significantly restricts the exploration and development of global oil and gas resources. Predicting lost circulation risk in fractured formations enables the targeted optimization of both well trajectory design and wellbore strengthening strategies, thereby reducing the frequency of such occurrences. Fracture aperture and intensity interpreted from imaging logging are used to develop an analytical model for the fracture complexity index (FCI) through the analytic hierarchy process and entropy weight method, reflecting fracture development and internal heterogeneity. Given the limited length of the imaging logging intervals, fracture aperture is used to calibrate the response relationship of resistivities acquired from dual laterolog logging. This results in an empirical model for evaluating fracture aperture using dual laterolog resistivities in the absence of imaging logging, thus enabling the calculation of the FCI. Finally, a 3D FCI model is constructed using Kriging interpolation constrained by the seismic ant-tracking discontinuity attribute. The 1D FCI profile for the drilled wells was calculated using the above method and compared with the imaging logging maps. The results show that a larger FCI is associated with a higher number of fractures or greater fracture aperture at the corresponding depth in the imaging logging maps. Previous studies have indicated that both a greater number of fractures and wider fractures increase the incidence of lost circulation in the field. Therefore, the new FCI model provides a viable approach for predicting lost circulation risk in fractured formations. Subsequently, the lost circulation depths of the drilled wells were predicted using the spatial distribution and cross-well sections of the 3D FCI attribute. The prediction results for lost circulation risk are in good agreement with the actual lost circulation depths observed in the field, further confirming the reliability of the prediction model. The novelty of the risk prediction model lies in its systematic integration of both fracture aperture and intensity effects on lost circulation mechanisms. This approach addresses the limitations of conventional risk prediction methods, which predominantly rely on a single fracture characteristic parameter such as fracture intensity, resulting in low prediction accuracy and limited applicability in frontier exploration areas. This innovative methodology provides technical support for mitigating potential lost circulation risks and optimizing drilling design.