Understanding drilling induced fractures

Abstract

Oil and gas production is moving to harsher geological conditions such as deep water drilling and high-pressure high-temperature reservoirs, so accurate knowledge of wellbore stability is crucial. The main causes of wellbore instability are high pore pressure in the formation, drilling induced disturbance of stable formations and the possible chemical reactions between the reservoir formation and the drilling and completion fluids. The thesis has studied the occurrence of drilling induced fractures, which can eventually cause fluid losses to the formation, hence become a costly issue during drilling. Borehole image tool are the only tool as of today that can detect drilling induced fractures, however one would like to prevent them from occurring. The thesis is interested in examine what can be the primary effect of their occurrence, and have chosen to focus on the effect of temperature. A new fracturing model was also introduced in this examination, where three scenarios were developed. These scenarios provided important information on the fracture gradient’s sensitivity towards temperature. Finally, the coefficient of thermal expansion was suggested to investigate further as it may have a bigger impact on the fracture gradient than initially presumed. Additionally, the importance of time-dependent downhole MWD data along with effective ECD management was accentuated.