Quantitative prediction of tertiary formation fractures and its application in lost circulation prediction in the Bozhong Depression

In recent years, the exploration and development of oil and gas reservoirs in the Bohai Sea have gained significant attention. However, the high cost of offshore drilling and the occurrence of frequent lost circulation accidents have resulted in substantial economic losses. Therefore, it is crucial to effectively predict and assess the risk of lost circulation in the Bozhong Depression. This study focuses on the analysis of lost circulation characteristics, identifying fracture characteristics as the most influential factors. Geomechanical methods were employed to characterize fracture parameters in the study area, enabling the prediction of lost circulation. A three-dimensional heterogeneous rock mechanical parameter model, incorporating lithology and faults, was constructed based on rock mechanics experiments, logging, and seismic data. Structural evolution analysis and acoustic emission experiments were conducted to determine the main period of fracture development. The Ansys software's finite element simulation platform facilitated the simulation of the paleo-stress field in the study area. By applying the principles of geomechanics, a calculation formula for fracture parameters was derived, and the spatial distribution of fracture parameters in the study area was quantitatively characterized using the results of the paleo-stress field simulation. Taking into account the lost circulation points of drilled wells, fracture parameters, current stress field, lithology, and other factors contributing to lost circulation, a leakage risk threshold area for fracture parameters was proposed. The predictions of lost circulation were validated using verification wells, demonstrating good agreement with actual drilling conditions. This approach provides valuable insights for mitigating lost circulation during drilling, reducing drilling cycles, and minimizing economic losses.