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Sediments frequently appear at the bottom of oil and gas wells in the bottom of carbonate rocks during completion or production, seriously affecting the productivity. In order to solve the wellbore cleaning problem, this article applies the Bernoulli equation theory method, the finite element method based on the standard turbulence model and the laboratory test to verify a kind of negative pressure wellbore cleaning tool which can establish local reverse circulation under the action of high-pressure water jet and salvage the bottom debris. Through the numerical analysis of the cleaning tool structure, it is found that the wall face diameter is at least two times of the nozzle hole diameter to effectively play the cleaning tool performance. If the total area of nozzle outlet is 48π mm 2 , the cleaning tool fishing capacity of six nozzle structures is improved the most. The analysis of the adaptability of the cleaning tool shows that the cleaning tool with an outer diameter of 104 mm is most suitable for the casing shaft with an inner diameter of 127.3 mm. The cleaning tool was applied to the field operation and successfully cleaned the wellbore, effectively increasing the wellbore productivity.

Ovalization, as an important factor affecting the performance of flexible pipes, is unavoidable in the manufacturing process. In this paper, a model of a flexible pipe with initial ovalization is established numerically. The numerical model is verified by a case analysis, and the influence of ovalization on the torsional response of a flexible pipe is discussed. It is found that the ovalization always has a negative effect on the torsional stiffness of the flexible pipe. Then, the effective numerical model is used to calculate the torsional response of a flexible pipe with initial ovalization under dry and wet annulus pressure. It is found that the dry annulus pressure improves the torsional stiffness of the flexible pipe by advancing the interaction between the layers and hindering the radial expansion of the outer tensile armor layer. However, the dry annulus pressure also increases the stress of the tensile armor layers, which reduces the withstanding capacity of the flexible pipe. Especially with the increase of ovalization, the loading capacity decreases more obviously. The wet annulus pressure has little effect on the torsional response of the flexible pipe, but it extends the risk of radial collapse of the carcass layer. [ABSTRACT FROM AUTHOR]

• An effective equivalent model was proposed for flexible pipe. • The correctness of the FEM was verified by experimental. • The axial elongation of the flexible pipe in tension shall be less than 1.3%. • The influence of hydrostatic pressure on the tensile properties of flexible pipes with different initial ovality is discussed. Flexible pipes play an important role in the transportation of oil and gas from the seabed to floating production units. They are also employed to inject water or gas into offshore wells. In deep-sea oil and gas extraction, flexible pipes must be able to withstand very high tensile and hydrostatic pressures. In this paper, an equivalent method is used to represent the complex carcass layer and the pressure armor layer as a regular cylinder, and then a numerical model of a 2.5" flexible pipe was developed and verified by experiment. A tensile analysis of flexible pipes with different degrees of initial ovalization indicated that ovalization of 0–1% does not affect the tensile rigidity, but increasing the ovalization creates an uneven load and stress concentration on the tensile armor layer. When a flexible pipe is subjected to hydrostatic pressure, the outer pressure increases the tensile rigidity of the flexible pipe more than the annular pressure, but the reduction of the ultimate tensile load is clear. A high annular pressure can cause the collapse of the carcass layer. [ABSTRACT FROM AUTHOR]