Lithology effects on the fractures parameters using image log and petrophysical data

Abstract

Fractures within a reservoir play an influential role in the porosity and permeability, therefore affect the fluid flow. By analyzing properties of fractures, such as fracture height, density and mutually spacing and compare them with different tectonic locations and different lithologies, one could gain insight in the mechanical behavior of a rock mass, when distorted by tectonic forces. The velocity deviation log (VDL) can be used for determination of effective porosity. The result indicated that there is a high fractures density in the Asmari Formation which shows high correlation with VDL. They are mainly strike N75E, S75W direction and are chiefly observed in the upper Asmari zones. Fractures and vuggy have been also observed in the well. Image log showed a range of bedding dip from 53-89 degree with strike N55W, S55E in the well indicating of reverse limb in the field. Image log show tow set fracture which azimuth 347 for discontinuous fracture and 220 with strike N55W, S55E for continuous fracture. Main type of lithology determined by petrophysical log showed that dolomite is dominant constituent. Induced fractures and breakouts haven't seen observed in this well. After correlating image logs with VDL and lithology, zones with dominant pure dolomite presented higher aperture rather zones with dolomite and anhydrite. Fracture density is more affected by bed thickness to mineralogy. Zones with negative deviation velocity have high fracture density or high fracture aperture.

Determination of Key Beds from the Cap Rocks of Oil Reservoirs Using a Novel Method, Case Study: The Gachsaran Formation, Southwest Iran

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