Developing a geomechanics-modeling based method for lost circulation risk assessment: A case study in Bohai Bay, China

As a challenging engineering problem, the lost circulation in fractured formations seriously hinders the efficient development of oil and gas wells. Clarifying the weak layer is the key to improve lost circulation prevention and remediation. Nevertheless, due to the complexity, randomness, and interference of engineering factors, a mature lost circulation prediction method of fractured formation has not yet been formed. This work, based on geomechanical modeling, combining with logging and seismic data, constructs the three-dimensional fracture intensity spatial distribution, the three-dimensional minimum in-situ stress spatial distribution, and the three-dimensional brittleness index spatial distribution of the target oilfield, respectively. At the same time, the analytic hierarchy process is used to establish a three-dimensional lost circulation risk index of the target oil field, and a classification evaluation standard for lost circulation risk is proposed. This method is applied in the Bohai A oilfield, the three-dimensional lost circulation risk index of the entire oilfield are established. Three hundred seventy-seven lost circulation sample points of drilled wells are selected, and a classification evaluation standard for lost circulation risk is established for the Bohai A oilfield. The research results show that the classification evaluation standard for lost circulation risk has good guiding significance for subsequent drilling in this area. It can scientifically guide the design of well trajectory and well structure of subsequent wells, and improve lost circulation prevention.