Safety Distances of Packers for Deep-Water Tubing-Conveyed Perforating

摘要

The technologies of high density and high charge perforator are widely used in the perforation jobs of deep-water wells, resulting in a large increase of impact loads in the wellbore. Determining the safety distances between the packers and the perforating gun is a critical step for developing completion designs of deep-water. This paper examines the processes of pressure wave generation, attenuation and reflection propagating through the completion fluid during wellbore perforation and develops a calculation model to formulate safety distances of the packers to protect the non-perforated wellbore. A calculating model containing an unknown function is established, which is used to solve the safety distances of packers and a mathematical model based on numerical simulation results is proposed to predict the peak pressure on the perforating gun, which can evaluate the sensitivity of peak pressure to changes under different conditions of perforation. The complete calculating model for determining the safety distances of packers is finally created. The results of case study show that the predicted peak pressure by the model is accurate, within 10% of measured values by a pressure sensor installed at the bottom of the perforating gun during a well completion job within the South China Sea. This calculating model indicates that the attenuation law of the pressure wave propagation in the completion fluid basically accords with the exponential attenuation mode, which is verified by the data of underwater explosion experiment. The number of perforating bullet, charge per hole, tubing length, formation pressure and wellbore pressure are important factors of the safety distances. According to the numerical simulation results of the field example, the shock absorber has the optimal installation position, which the ratio R_0/R=0.6 being the best shock absorption effect can be achieved. This study proposes a novel method for the safety distances design of packers and the location of the absorber is optimized, which has important significance to provide guidance for the design of deep-water perforating operations and to improve security.