Currently, there is no proper method to predict the pore pressure disturbance caused by multistage fracturing in shale gas, which has challenged drilling engineering in practice, especially for the infilling well drilling within/near the fractured zones. A numerical modelling method of pore pressure redistribution around the multistage fractured horizontal wellbore was put forward based on the theory of fluid transportation in porous media. The fracture network of each stage was represented by an elliptical zone with high permeability. Five stages of fracturing were modelled simultaneously to consider the interactions among fractures. The effects of formation permeability, fracturing fluid viscosity, and pressure within the fractures on the pore pressure disturbance were numerically investigated. Modelling results indicated that the pore pressure disturbance zone expands as the permeability and/or the differential pressure increases, while it decreases when the viscosity of the fracturing fluid increases. The pore pressure disturbance level becomes weaker from the fracture tip to the far field along the main-fracture propagation direction. The pore pressure disturbance contours obviously have larger slopes with the variation of permeability than those of the differential pressure. The distances between the pore pressure disturbance contours are smaller at lower permeability and higher viscosity. The modelling results of the updated pore pressure distribution are of great importance for safe drilling. A case study of three wells within one platform showed that the modelling method could provide a reliable estimation of the pore pressure disturbance area caused by multistage fracturing.
In order to control and monitor downhole equipment, it is needed to inject cable into coiled tubing. Being directly against the drawback of the traditional injecting method, a new method of adding pressurized water has been put forward. By using Workbench software, this paper researched the regular pattern that water flow’s pressureaffects cable in coiled tubing after it has various deformations in both entrance and main part of coiled tubing, taking 25mm diameter coiled tubing with 3mm diameter cable as an example. It also simulated the effects of water flow toward cable in coiled tubing as well as how the different diverging distances of entrance for injection affects the speed of cable during injection, taking 50.8mm diameter coiled tubing with 5.6 mm diameter cable as an example. It determined the optimal position of cable entrance and provided the theoretic foundation for the possibility and practical manipulation of the new method for injecting cable into coiled tubing.
As injector injects coiled tubing into well to a certain depth, the coiled tubing is unable to be injected continuously because of the increasing friction between the coiled tubing and the wellbore. With the core technology being an effective role in the Coanda Effect control switch, the Water Hammer Vibrator may extend the depth of the coiled tubing into the wellbore. Firstly, the paper verifies the effectiveness of the Coanda Effect control switch in Water Hammer Vibrator. Secondly, it optimizes the structure of the Coanda Effect control switch and improves the driving force of the piston of the water hammer vibrator without changing the injection flow rate, pressure and the other boundary conditions. Finally, it obtains varying patterns of the hydraulic cylinder pressure at both ends in the process of the Coanda feedback and trigger action by the experiment of the Coanda Effect control switch to measure pressure at both ends of hydraulic cylinder with the NI data acquisition unit. The results confirm the validity of the optimized Coanda Effect control switch in water hammer vibrator, so as to ensure the implementation and improvement in the water hammer effect of Water Hammer Vibrator.
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