RE: SP3 Dec 2019 19:17
Perhaps worthy of consideration, when referencing the potential for further utilising an existing well bore to perform a side track for instance in wells in a more conventional reservoir, perhaps we should consider why that may not be optimal in a fractured basement reservoir.
The critical consideration in fractured reservoirs is the fracture matrix, and the more fractures that are transversed, and the size (width, length, and depth, i.e. volumetric) of those fractures, and the orientation (by both the orientation of the x axis, and the y axis) of the same, if the production is to be prolific.
In conventional reservoirs (such as a sandstone, for example), the primary considerations are merely two dimensional, depth of producible reservoir sand, and distance in a horizontal plane from the reservoir interception point.
Yes, there are other considerations, such as OWC depth, suitable quantity and location of traps, etc., but they are common to both conventional, and fractured, reservoirs, so I have excluded them from consideration when defining the variables in relation to those aforementioned reservoir types.
So, sidetracking to a potentially more prolific (could be updip, downdip, or going closer/further away from the attic, etc.) part of a conventional reservoir could be achieved by a sidetrack change to well bore heading, or to sidetrack either shallower or deeper to achieve a change to place the wellbore shallower (nearer the attic), or deeper (closer to the OWC, or to explore a different formation deeper down).
However, due to the criticality in a fractured basement of traversing the fractures on a very specific heading, to ensure that the maximum number of previously identified (they have a reasonably good idea of the fracture matrix, they don’t just drill blind) fractures are traversed, you cannot simply change the heading of the sidetrack to achieve success, as a 90 degree change of heading would have you running down between the previously identified fractures instead of traversing them, and unless you intersect these fractures you are merely drilling a wellbore through an impervious (consequently zero porosity, and zero permeability) rock formation.
There may be a benefit of sidetracking shallower if the fractures were full of infill, as may have been seen on the WD well, but in this instance the WW well was drilled towards the attic/crest, so no benefit in sidetracking shallower.
The above reasons are why I believe that wellbore in conventional reservoirs have the potentially benefit from latterly being sidetracked once the reservoir is better known, but why I believe that potential benefit will not benefit from latter re-entry, and why I believe that in a fractured basement reservoir you wouldn’t/couldn’t re-use the wellbore, and you would drill a new one latterly.
All the above is purely IMHO, I anticipate it being ripped to shreds, but perhaps it is the nucleus for a discussion on the subject.