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

Abstract

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. • Combining logging data, seismic data, and actual drilling data of Bohai A oilfield, this work makes a clear relationship between rock mechanics environment, rock brittleness, fracture development intensity, and lost circulation. • This work uses geomechanical modeling methods to calculate the spatial distribution of 3D fracture intensity, 3D minimum in-situ stress, and 3D brittleness index of Bohai A oilfield. Further, a three-dimensional lost circulation risk assessment index is constructed based on the analytic hierarchy process. Moreover, according to the lost circulation data of drilled wells, a classification evaluation standard for lost circulation risk in Bohai A oilfield is formulated. • This work comprehensively considers the main factors affecting loss, fully reflects the lost circulation characteristics, and quantitatively predicts the fracture lost circulation zone of the formation.