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Iterative Method of Computing Pressure Loss in Horizontal Wells |
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Iterative Method of Computing Pressure Loss in Horizontal Wells Authors: Z. Gacek, A. Olajossy
Downhole dynamic pressure is a key parameter required to determine the reservoir features or to
determine the necessary conditions for production. These are of major importance in hydrodynamic calculations
to fi nd the basic parameters of reservoir rock, to determine well locations and the optimal spacing
between boreholes and the optimal rate of production on the reservoir rock level. The authors made an
attempt to fi nd the downhole dynamic pressure and pressure loss in a horizontal well in the conditions
of single-phase gas fl ow and stabilised fl ow in the reservoir. As density, viscosity and compressibility
of gas depend on its pressure and temperature, the analytical solution for gas fl ows is more complicated
than for fl ows of incompressible fl uids. Furthermore, the fl ow of gas through a perforation in the production
section of a horizontal well will interfere with the stream of fl owing gas and bring about a change
of the fl ow resistance along the well. Pressure in a horizontal well is governed by the energy balance
equation. An analytical solution to this equation for the fl ow of gas requires that temperature-dependent
gas parameters (i.e. viscosity, compressibility and resistance to fl ow) should be averaged, which might
lead to further errors. Besides, in thus obtained solutions to the energy balance equations, the averaged
parameters are related to pressure. That is why an iterative procedure was applied to obtain the static and
dynamic pressure. The iterative algorithm was further utilised and an application was written in Borland
Pascal that computes pressure losses in horizontal wells. This application might be employed to compute
pressure losses in vertical and directional wells. Pressure loss in the well is determined for particular
well sections and pressure implicitly present in the formulas is obtained by successive approximations.
Resistance due to gas fl ow through a perforation is determined by adjusting the linear friction coeffi cient
utilising the Quyang’s correlation procedure. It is demonstrated that in the case of single-phase fl ows
of gases the downhole pressure can be derived from well production data with suffi cient accuracy. The
adequacy of the proposed method is verifi ed by a computation data for a real case. |
2011