Putting together some conceptual models of your fracture network will save you a lot time during the fracture modelling process. These are important to capture the range in fracture distribution and the type of fractured reservoir (Nelson classification - Figure 1). This is crucial in the absence of a well test, as fracture permeability will be highly uncertain and the relative role of fracture and matrix is unknown.
Figure 1. Nelson classification of fractured reservoirs.
Check out the available data to see what the potential drivers are for fracture occurrence throughout the reservoir. Faults can be a good place to start as fractures often cluster around faults - cored (or picked on image log) fractures close to a seismically resolvable fault may be the basis of a fault-related fracture conceptual model (Figure 2). Based upon this, assign a probability to this conceptual model (Figure 3). However, this may only be observed in 1 well, so other fracture descriptions/drivers are possible. The downside could be matrix only flow (Type IV of Nelson, Figures 1, 3), whereas the upside has a high density of fractures around faults and background fractures (Type II of Nelson ?, Figure 1).
In fold and thrust belts, fold-related fractures are common i.e., fractures that form as a result of the folding process - not from the far-field stresses that cause the fold in the first place (see blog - fold-related fractures). Conceptual models such as the Price (1966) and Stearns (1972) models are particularly useful in giant folds which only have a few well penetrations.
Figure 2. Conceptual model of fractures around a fault. Modified from Johri et al (2014).
Figure 3. Conceptual models showing a range of possibilities during the appraise stage. CASE 2 AND 3 DIFFER IN THAT SAND-SAND COMMUNICATION ACROSS THE BLACK FAULT IS POSSIBLE IN CASE 2 BUT NOT IN CASE 3 AS CONTENT OF THE FAULT ROCK CAUSES SEALING.
Reference
Johri, M, Zoback, M.D, Hennings, P. 2014. A scaling law to characterize fault-damage ones at reservoir depths. AAPG Bulletin, V.98 (10), p 2057 – 2079.
Stearns D.W. & Friedman, M. 1972. Reservoirs in fractured rock. In: Stratigraphic oil & gas fields – classification, exploration methods and case histories. R.E. Kring (ed). AAPG Memoir, 16, 82-106.