Are there any references whereby we can get the details on (A) pressure in the vicinity of well; (B) pressure at the radius of influence; (C) the length of radius of influence; (D) the well radius; (E) the fluid compressibility.
Whether the fluid flow in a fractured reservoir is going to be hyperbolic dominant as against the conventional diffusive based parabolic dominant scenario??
I assume we are talking about a naturally fractured reservoir, and (to avoid mixing the matrix response with the fracture response) of a Type 1 fractured reservoir (fractures provide the essential reservoir porosity and permeability. R.A. Nelson, "Geologic analysis of naturally fractured reservoirs").
All depends on the natural fracture network and the existing fracture sets, and on the well geometry (vertical well or horizontal well).
If the open fracture sets are perpendicular to each other and have the same parameters (spacing, aperture, horizontal permeability), you can assume an isotropic pressure field in the open fracture space around the producing vertical borehole, with a drawdown pattern having circular symmetry. This case is however rare, the norm being an asymmetric fracture network, with a predominant open fracture direction and therefore a dominant direction of horizontal permeability.
In the latter case (one dominant open fracture set), the drawdown pressure pattern around a producing vertical well is likely to be elliptical (in map view), with the ellipse axes being proportional to the two components of the horizontal permeability of the fracture network.
One way to assess the anisotropy of the horizontal permeability in fracture networks is to construct a Discrete Fracture Network (DFN) computer model and to extract from it horizontal permeability in two main directions, i.e. in the direction of the main open fracture set, and in the direction perpendicular to it (or, at least, the ratio between the two horizontal permeability, minimum and maximum).
If you want to analyse a horizontal well, the direction of the horizontal well segment relative to the dominant fracture set is crucial. Let’s assume that the horizontal well is drilled in a direction perpendicular to the dominant fracture set. In this case, the extent of the zone of influence (drainage area) is maximum in a direction perpendicular to the well horizontal section (along the dominant fracture set) and minimum ahead of the well tip or behind the well heel (across the dominant fracture set) , and it would be at least as long as the reservoir penetration.
Thanks Dr Bencini - for your reply. Yes I agree with you. For Type 1 NFR, we can very well use the concept of MINC - where we will have the isotropic pressure field as you have mentioned. Even a conditional anisotrophy works well with DFN modeling - where we will be able to get the elliptical pressure distribution as a function of maximum and minimum horizontal permeability. Investigation of the pressure field in the presence of a horizontal well is quite complex, and for the time being, I am looking for the details of some field data in this direction. My intention is to understand whether the fluid flow within a fractured reservoir remains diffusive (parabolic) or conservative (hyperbolic). Thanks again for your time and detailed reply.
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