Finite element analysis to investigate the success probability of stress cage technology relative to regime of in-situ stresses for control of drilling fluid lost circulation

Drilling fluid lost circulation into underground formations, in areas of high permeability, formations with natural fractures, and weak formations is one of the common problems in oil and gas well. Some researches show that about 20% of the non-productive times during drilling operations are due to lost circulation. Generally, the remedial and preventive methods are the two main approaches to deal with the problem of lost circulation. One of the methods of preventing drilling fluid lost circulation is to use the stress cage method in order to increase the formation fracture pressure around the well. Several factors including rock mechanical parameters, properties of bridging materials, stress regime, and properties of drilling fluids are significant in the effectiveness of the technology. In this research, the influence of the horizontal stress ratio on the effectiveness of the stress cage technology has been investigated. For this purpose, first, the three-dimensional model of the well is presented, taking into account the elastic behavior of the rock, and then the tangential stress changes in two states before creating a fracture and after bridging the fracture have been investigated. The results showed that, based on the data used, the application of this technology leads to an increase of 3618 psi in the tangential stress at the wellbore wall and, as a result, an increase in the formation's fracture pressure. In weak formations, this prevents induced fractures and drilling fluid lost circulation. Also, the maximum tangential stress was observed at bridging location of 0.5 inches from fracture aperture. On the other hand, the results showed that the stress cage’s effectiveness depends on the horizontal stress ratio. Based on the results of the numerical model, at the maximum horizontal stress to minimum horizontal stress ratio of greater than 0.715, the stress cage technology effectively increases the tangential stress.