Analysis of Fractures in the Reservoir Rocks of the Karanj Oil Field in Southwest Iran

Abstract

Dezful Fractures exert a critical influence on global fluid flow dynamics in carbonate reservoirs. Our study concentrated on fractures in two wells in the Karanj oil/gas field in the southern Embayment of the Zagros Basin, utilizing FMI image logs across the Gachsaran and Asmari Formations. A notable finding was the highest bedding frequency identified in Zone 1-1 of the Asmari Formation. In this rock section, 44 open fractures were identified – 7 medium, 22 minor, and 15 hairline fractures – with dips mainly between 63 to 85 degrees. Notably, the absence of borehole breakout due to low horizontal stress was observed. Instead, induced fractures consistently followed a prevailing N75E/S75W trend, aligning with regional stress patterns. Bed dips ranged from 21 to 57 degrees, averaging at 12 degrees towards S38W, with strikes at N52W/S52E. Zone 1-1 of the Asmari Formation exhibited the highest bedding frequency. Expanding our analysis to the entire Karanj field’s reservoir rock, a total of 703 open fractures were identified, showing dips from 21 to 80 degrees. A significant observation was a potential fault at 1536.5 m, characterized by a strike of N45E-S45W and a dip of 75 degrees in the S45E direction. At depths of 2276.85 and 2279.5 m, fault evidence was also noted in the image logs. This research significantly contributes to our understanding of fracture patterns in carbonate reservoirs, providing valuable insights into fluid flow dynamics.