Abstract

Many methods of fractured well representation in simulation model are known. Some of them are too complex to use in large simulation model where more then one well are fractured, some don't represent a fractured well behaviour. In this work a choise of a fractured well representation in simulation model have been proceded from the practical point of view. A method of fractured well simulation model assessment in situation with lacking production history was created. It is based on comparison of productivity and transient pressure behaviour with results of analytical model of Cinco-Ley and Samaniego.

Analysis of the known methods of the hydraulic fractured well simulation

First of all several methods of hydraulic fracture representation are analysed form the practical point of view: in simulation model with almost 1 million cells futher significant complication of grid is undesirable. Also numerical problems with system of linear eqations solution in case of very thin fracture cells should be solved too.

Representation of the hydraulic fracture flow by the well skin factor:

The method of fractured well representation with skin-factor setup is one of the simplest methods. Increased inflow from the relatively high permeability fracture can be represented by fractured well skin factor, calculated by Cinco-Ley and Samaniego formalism [2,3] or by another theory. The main problem associated with this method is the indifference to fracture direction. This feature can be neglected if the fractured well stands alone in the field or fracture dimesions are negligible in comparison with distance to a nearest well, but it is very important when there is a pattern of the fractured wells and fracture dimensions cannot be neglected. So in this situation, when the pattern of the fractured wells have to be represented in the simulation model this variant of the hydraulic fracture flow simulation is not appropriate.

Representation of the hydraulic fracture flow by the Cartesian local grid refinement:

To represent the behavior of the fluid inflow from the relatively high permeability but rather narrow fracture, coarse cells in simulation model can be locally refined (near the wellbore) and permeability of some of them can be modified as shown on Fig 1 (red area in figure - area of changed permeability). It is evident, that Cartesian local grid refinement can be made only in three directions - directions of axis of simulation grid. To use Cartesian local grid refinement a direction of one of the axes of simulation grid should coincide with minimal formation stress direction. Also it is evident that with Cartesian local grid refinement a thinning of a fracture from perforation holes to tip cannot be represented. But main advantage of this method is change of flow direction - flow is no more radial.

To summarize all written it can be said that main advantages of this type of fracture flow representation are:

  1. Relative simplicity of realisation;

  2. The direction of the fracture propagation can be taken into account;

Disadvantages:

  1. Only two direction can be modelled;

  2. Cells are rectangular in the shape with the uniform width;

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