Integrated fracture characterization of Asmari reservoir in Haftkel field

Kourosh Khadivi,Hamed Hassani,Saeed Dehghani,Sadegh Sanjari,Hashem Fardin,Mohammad Partovi,Mojtaba Alinaghi,Mansour Shiralipour,Seyed Chaseb Mosavi,Mehrbod Soltani

doi:10.1007/s13202-021-01435-4

Abstract

The Asmari reservoir in Haftkel field is one of the most prolific naturally fractured reservoirs in the Zagros folded zone in the southwest of Iran. The primary production was commenced in 1928 and continued until 1976 with a plateau rate of 200,000 bbl/day for several years. There was an initial gas cap on the oil column. Gas injection was commenced in June 1976 and so far, 28% of the initial oil in place have been recovered. As far as we concerned, fracture network is a key factor in sustaining oil production; therefore, it needs to be characterized and results be deployed in designing new wells to sustain future production. Multidisciplinary fracture evaluation from well to reservoir scale is a great privilege to improve model’s accuracy as well as enhancing reliability of future development plan in an efficient manner. Fracture identification and modeling usually establish at well scale and translate to reservoir using analytical or numerical algorithms with the limited tie-points between wells. Evaluating fracture network from production data can significantly improve conventional workflow where limited inter-well information is available. By incorporating those evidences, the fracture modeling workflow can be optimized further where lateral and vertical connectivity is a concern. This paper begins with the fracture characterization whereby all available data are evaluated to determine fracture patterns and extension of fracture network across the field. As results, a consistent correlation is obtained between the temperature gradient and productivity of wells, also convection phenomenon is confirmed. The findings of this section help us in better understanding fracture network, hydrodynamic communication and variation of temperature. Fracture modeling is the next step where characteristics of fractures are determined according to the structural geology and stress directions. Also, the fault’s related fractures and density of fractures are determined. Meanwhile, the results of data evaluation are deployed into the fracture model to control distribution and characteristics of fracture network, thereby a better representation is obtained that can be used for evaluating production data and optimizing development plan.

Highlights

The Asmari reservoir in Haftkel field is one the best examples of the Naturally fractured reservoir (NFR) in the world where the desired reservoir engineering elements are found during the 93-year production history of this field
We present fracture characterization at first, where all available data including petrophysical logs, oil production, productivity index, saturation pressure, as well as temperature and pressure surveys are reviewed to obtain a holistic view of fracture network
High temperature gradient records are found at the edges where the lowest fracture density is anticipated

Summary

Introduction

The Asmari reservoir in Haftkel field is one the best examples of the NFRs in the world where the desired reservoir engineering elements are found during the 93-year production history of this field. It is located in the Northern Dezful Embayment in the southwest of Iran (Fig. 1) in the center of the chain of anticlinal structure of Asmari which extends Mamatain in the southeast to the Naft-Safid in the northwest. Gas injection was commenced in 1976 to maintain reservoir pressure and stabilize contact levels

Objectives

Findings

Conclusion