An advanced wellhead device for shock-wave treatment of the bottomhole zone

A newly designed wellhead device has been developed in order to reduce filtration resistance and restore the reservoir-to-well connectivity for shock-wave impact on the bottomhole formation zone. The device can be used for enhanced recovery of crude oil by reservoir stimulation through the well while well completion and well repairs. In this paper, the problem of increasing the frequency of closing and opening the wellhead device is solved through a reliable design and a constant and continuous lower pressure compressed air supply, which allows it to be used to create pressure and rarefaction shock waves in the well. The use of the developed device allows to put into production low-permeability and isolated zones, improving connectivity and thereby facilitating filtration in the «reservoir-well» system, which boosts enhanced oil recovery and reduces oil cost.

The piston problem in hyperelasticity with the stored energy in separable form

The piston problem for a hyperelastic hyperbolic conservative model where the stored energy is given in separable form is studied. The eigenfields corresponding to the hyperbolic system are of three types: linearly degenerate fields (corresponding to the contact characteristics), the fields which are genuinely nonlinear in the sense of Lax (corresponding to longitudinal waves), and, finally, nonlinear fields which are not genuinely nonlinear (corresponding to transverse waves). Taking the initial state free of stresses, we presented possible auto-similar solutions to the piston problem. In particular, we have shown that the equations admit transverse shock waves having a remarkable property: the solid density is decreasing through such a shock, it is thus a ‘rarefaction’ shock.

The admissibility domain of rarefaction shock waves in the near-critical vapour–liquid equilibrium region of pure typical fluids

Application of the scaled fundamental equation of state of Balfour et al. (Phys. Lett. A, vol. 65, 1978, pp. 223–225) based upon universal critical exponents, demonstrates that there exists a bounded thermodynamic domain, located within the vapour–liquid equilibrium region and close to the critical point, featuring so-called negative nonlinearity. As a consequence, rarefaction shock waves with phase transition are physically admissible in a limited two-phase region in the close proximity of the liquid–vapour critical point. The boundaries of the admissibility region of rarefaction shock waves are identified from first-principle conservation laws governing compressible flows, complemented with the scaled fundamental equations. The exemplary substances considered here are methane, ethylene and carbon dioxide. Nonetheless, the results are arguably valid in the near-critical state of any common fluid, namely any fluid whose molecular interactions are governed by short-range forces conforming to three-dimensional Ising-like systems, including, e.g. water. Computed results yield experimentally feasible admissible rarefaction shock waves generating a drop in pressure from 1 to 6 bar and pre-shock Mach numbers exceeding 1.5.