Research Of Well Kick And Loss Circulation Rule Of Gas-liquid Gravity Displacement On Carbonate Formation

Well kick and loss occur frequently in the process of drilling due to abundant fractures and cave in carbonate reservoirs.There are also loss circulation and well kick coexisting caused by gas-liquid gravity displacement.The gas-liquid gravity displacement is the phenomenon that the drilling fluid enters the fracture and gravity displacement happen between drilling fluid and the gas due to their density difference so that drilling fluid leak into the formation,while the gas enter into the wellbore.The phenomenon of loss circulation and well kick coexisting makes the overflow and leakage become more complex.At present,there is little research on the gas-liquid gravity displacement,and lack of systematic theory and experimental simulation.Firstly,the experimental research of gas-liquid gravity displacement has carried out.Based on the characteristics of fracture-cave units in carbonate reservoirs,a visual experimental device for gas liquid gravity displacement is developed.The phenomenon of gas-liquid gravity displacement was simulated,and the gas-liquid interface was observed clearly,also exploring the influence factors.Then,in order to supplement the rule of influence factors which is unable to obtain because of the limitations of the experimental conditions,numerical simulation is applied to further analyze the process of gas-liquid gravity replacement.The results show that the fracture length and height have little effects,and the increase of the width promote the occurrence of gas-liquid gravity displacement.The influence of drilling fluid density is small,while the increase of viscosity will restrain the occurrence of gas-liquid gravity displacement.The fluctuations of wellbore pressure will affect the kicking-lossing rate,while the drilling degree of fracture also will influence the rate by changing flow channel size.Finally,based on the results of the visualization experiments and numerical simulation,the conditions for the occurrence of gravity displacement are analyzed.The gravity displacement window in the case of fracture and cave is established,and the prevention measures of gas-liquid gravity displacement are presented combining with field examples.In this paper,the occurrence,development and influence factors of gas liquid gravity displacement are revealed by experiments,numerical simulation and theoretical analysis.It provides a theoretical basis for safe drilling of carbonate reservoir.