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To solve the insufficient energy for reverse circulation fishing tools in complex structure wells, it is necessary to further optimize the design of the tools to improve the impurity salvage efficiency. In this work, a three‐dimensional (3D) flow field simulation model of reverse circulation fishing tool with venturi negative pressure is employed to identify the vortex zone of circulation channel and to investigate the negative pressure and jet velocity distribution around the spray nozzle based on the ANSYS‐CFX. The effects of the spray angle, diameter of the suction nozzle, and the nonstructural parameters on negative pressure and jet velocity are investigated through sensitivity analysis. As revealed from the results, there may be an optimum value for the spray angle, and the nozzle jet direction can indeed affect the propagation and attenuation of the bottom hole flow field greatly. The combination of the inner diameter of the nozzle outlet and that of the nozzle inlet (Φ + Φ′ = 3 mm + 6 mm) is the best design solution when the negative pressure at the nozzle outlet can be the highest. The negative pressure and jet velocity increase with the increasement of the inlet flow rate. The comparative analysis of different bottom hole impurity mass in the cases of the borehole inner diameter 5′ and 8.5″ on the salvage efficiency are conducted numerically. It is observed that the impurity mass salvaged and salvage time are not directly related to its total amount, but only related to the flow rate of the sucked fluid flow. The impurity salvage efficiency can be as high as 95.4%, which meets the engineering requirements in the field. This work improves the working performance of the reverse circulation fishing tool and provides theoretical guidance for well washing. [ABSTRACT FROM AUTHOR]

The radial jet drilling (RJD) technology is typically developed to open multiple lateral micro‐holes from a main wellbore to the formation. The multiple groups of 3D numerical models of radial micro‐holes through a main well are built by incorporating the pore hydro‐mechanical coupling effects. A number of sensitivity analyses were conducted on the effects of the radial jetting azimuth, the stress anisotropy, and the elastic anisotropy on the rock fracture initiation of the micro‐holes. As revealed from the results, the fracture initiation from the micro‐hole exhibited the diversified characteristics with the increase in the jetting azimuth of the micro‐hole. On the whole, the fracture initiation point was concentrated at the maximum principal stress. Thus, the jetting azimuth of the nozzle was recommended to be designed in the interval of 0°‐30°. A higher elastic modulus anisotropy ratio K and a lower Poisson's ratio anisotropy ratio K′ caused the significant rigidity characteristics of the rock, which increased the possibility of fracture initiation in the horizontal direction; a lower elastic modulus anisotropy ratio K and a higher Poisson's ratio anisotropy ratio K′ caused the strong rigidity characteristics, so the rock could not easily fracture in the vertical direction. Several suggestions were given that the rock is easy to be broken by selecting a smaller jetting azimuth angle and a more significant in‐situ stress difference. The numerical simulation results agree well with field experiment results, with an average accuracy of 97.17%. The proposed numerical model has a good performance in predicting the fracture initiation pressure of the radial micro‐hole in anisotropy formation. [ABSTRACT FROM AUTHOR]

A multi‐orifice nozzle is the primary actuator of radial jet drilling for the stimulation of unconventional and low‐permeability reservoirs. This research developed a 3D flow field simulation model to investigate the self‐propelled force of a multi‐orifice nozzle based on ANSYS‐CFX. To evaluate the self‐propelled ability of the nozzle, investigation was performed on the effects of the angle, number, the diameter of the forward and backward orifices of the multi‐orifice nozzle, and the diameter of the micro‐hole in the radial well on its self‐propelled ability by sensitivity analysis. The results revealed that the self‐propelled force slightly increased with the angle of forward orifice increasing, and decreased with the angle of backward orifice increasing; and that the self‐propelled force had a tendency to decrease significantly with the number of forward orifices increasing, and increased slightly with the number of backward orifices increasing. The self‐propelled forces for different combinations of forward and backward orifices were obtained by the simulation method, which agreed well with those obtained by the calculation method, with an average accuracy of 95.82%. It was observed that the self‐propelled force increased substantially as the value of K (d2/d1) increased, but tended to slow down when the flow rate was within a certain range. Besides, with the increase in the diameter of the micro‐hole, the self‐propelled force reduced, and increased substantially as the inlet flow rate increased, but tended to slow down as the inlet flow rate further increased. Thus, to ensure the self‐propelled ability of the jet nozzle, a set of optimal structural parameters can be used to generate the target self‐propelled ability. The research improves the working performance of multi‐orifice nozzles and provides theoretical guidance for hydraulic radial jet drilling process. [ABSTRACT FROM AUTHOR]

Obtaining the most Stimulated Reservoir Volume (SRV) by forming a complex fracture network is the prerequisite for shale gas hydraulic fracturing. In this paper, a coupled DFN–DEM model is presented based on a realistic discrete fracture network from fracturing treatment, to simulate the complex interactions between a created hydraulic fracture and a natural fracture system in shale. The sensitivity analysis of numerical simulation was performed to investigate the effects of hydraulic fracture length, multi‐fracture spacing, and internal friction angle on the stimulation reservoir area. The simulation results revealed that regardless of the DFN distribution and the length of hydraulic fracture, shear failure always tracked on the existing natural fracture plane. The amount and depth of the natural fracture shear into formation increased as the hydraulic fracture grew in length. Moreover, the actual dynamic morphology of fracture network was the radial or dendritic. A drastic change of permeability along the distance from injection may stimulate the fracture networks especially near the wellbore. For the multi‐fracture, the opening of the second fracture was able to stabilize the sheared fractures at the tip of the initial fracture. The shear failure area around the second fracture tended to increase with the growth of the length of the second fracture. Fracture network connectivity in the system is better for the optimal fracture spacing, and then fluid penetration during injection will influence the permeability evolution during stimulation. The stimulation reservoir area of the fracture network and the natural fracture friction angle had a quadratic relationship. Finally, the results by the data from field measurement in Sichuan, China verified that the proposed coupled DFN–DEM model had an accuracy up to 91.7%. The research results provide a reference for predicting the development of fracture network far away for multistage fracturing treatment. [ABSTRACT FROM AUTHOR]