Deviated Versus Vertical Wells in Complex Carbonate Reservoirs: Lessons Learned from Outcrops

Di Cuia, Raffaele ¹; Riva, Alberto ¹; Marian, Mara ¹
(1)G.E.Plan Consulting, Ferrara, Italy.

Carbonate fractured reservoirs are complex to understand and challenging to exploit economically because of the great difficulty of producing three-dimensional descriptions of fracture systems from subsurface datasets alone. The study of outcrop analogues can significantly improve the understanding of the distribution of fractures and their impact to the storage and flow of hydrocarbons in the subsurface and help in planning the appraisal and development drilling strategies.

The study of selected and appropriate outcrop analogues can help in better visualizing and understating the characteristics (type, vertical persistence, lateral extension, kinematics …) of the fault and fracture network and the geometric and age relationship between the different fracture families and the different structural hierarchical elements.

In the selected study area, located in the Apulian foreland, the carbonate sequences that appear monotonous in terms of geological and petrophysical characteristics are characterized by internal heterogeneities that affect not only the distribution of porosity and permeability, but also the fracture network in terms of orientation and density.

In this framework, large-scale faults and fracture corridors also play an important role. While small-scale bed-confined fracture could represent bed-parallel conduits, and medium-scale fractures connect several intervals, fracture corridors ensure the vertical connection over several tens of meters.

The selected outcrops are characterized by various faults with variable displacement (from few meters to some tens of meters). In general, fracturing is variable and becomes more localized close to faults. Fault zones are relatively narrow and characterized by intense fracturing in some cases developed only on one side of the fault plane. Coarse grained porous intervals (biogenic rudist bodies and calcarenitic beds) tend to show a lower fracture density than fine grained intervals, while faulting seems not to be influenced by lithological texture of the rock. Fractures and faults act as preferential fluid pathways.

In this kind of geological framework the trajectory of a deviated well can have a completely different response in the dynamic/production behavior that the trajectory of a vertical well because of the petrophysical characteristics of the units encountered. Moreover the location of the well trajectory (intersecting a major fault or not) will also have a different impact on the well performances

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.