Study on effect of fracture density on borehole stability and drilling fluid loss using Three-dimensional DEM-DFN method: A case study for SIE-01 borehole in Persian Gulf oilfield

Borehole instability in fractured formations and fluid loss during drilling is an important challenge for creating a stable drilling pattern in the oil industry. Understanding complex mechanisms and coupled hydromechanical phenomena which occur in fractured formation, needs to be more studies by using powerful approach such as distinct element methods. One of the main causes of fluid loss and increased in drilling costs, is the presence of fractures in the rocks. because of that, the investigation of borehole instability in fractured formation would be useful in determination of a safe methodology for drilling processes. In this paper, the simulation of the hydromechanical conditions of a borehole in fracture formation is carried out using Discrete Fracture Network (DFN) and Distinct Element Method (DEM). The modeling presented in this paper is based on real geomechanical and fractures characteristics in one of the boreholes in Persian Gulf oilfield. The model is validated using normalized yield zone criteria according to the caliper log data. The investigation of mud loss in the fracture network is based on changes in volume of spaces, between the discontinuities and non-compressible assumption for drilling fluid. In this paper, in other to understanding the effect of fracture density on borehole stability and fluid loss, six different scenarios for fracture density was investigated. The results showed, increasing the fracture density can be an absolute negative factor for instability in borehole. The numerical analysis shows that, in a specific range of fracture density, the overall mechanism of shear deformation in borehole would be different. However, the result of fluid loss analysis in fractured formation adjustment of borehole, showed that, by increasing the fracture density, volume of fluid loss increased continuously.