A Holistic Approach to Detect and Characterize Fractures in a Mature Middle Eastern Oil Field

Abstract

Naturally fractured reservoirs are recognized as challenging reservoirs to manage. The appropriate balance between production at acceptable oil rate and attaining high ultimate oil recovery is often difficult to find in these reservoirs. A good understanding of the fracture systems is essential for a successful development since the fractures significantly impact reservoir fluid flow and well productivity. Additionally, accurate fracture description in reservoir models is critical for reliable production forecasts. The main objective of this paper is to demonstrate a holistic approach to detect and characterize fractures in a mature oil field in the Middle East. The study was conducted by analyzing the dynamic data, such as production, reservoir pressure, pressure transient analysis (PTA), production logs, water salinity, drilling mud losses and image logs. The study results included evidence of fracture impact on field behavior, inter-reservoir communication and fracture properties quantification leading to recommendations for future reservoir management strategy and further development. The evidence of fracture impact on field behavior was evaluated through extensive analysis of well performance of more than 300 wells. The field consists of two reservoirs separated by a thick nonpermeable zone. The Upper reservoir is prolific, while the Lower reservoir is relatively tight and highly fractured. The communication between the two reservoirs was investigated by comparing Lower reservoir wells with the neighboring wells in the Upper reservoir. All available data were taken into account, including the production gas-oil ratio (GOR), reservoir pressure, and water cut profile and produced water salinity, as well as water breakthrough time. A material balance approach was utilized to confirm and quantify the communication between the two reservoirs. Data integration enabled deriving a series of probable links between the two reservoirs used for constructing representative fractures maps. Fracture conductivity was quantified using both pressure transient interpretation and production log results. The reservoir management team has utilized the study outcome to re-engineer the well architecture in both reservoirs. Additionally, active measures are taken to improve oil recovery from both reservoirs.

Analytical Modeling and Contradictions in Limestone Reservoirs: Breccias, Vugs, and Fractures

“…Reservoir engineers have assumed discontinuities as a type of pores regardless of their origin or genesis, and tectonic Journal of Petroleum Engineering fractures are considered as structural discontinuities impacting fluid flow [21]. So the discontinuities or heterogeneities such as vugs, tectonic fractures, and porosity associated with breccias can be interpreted with an equivalent medium [22].…”