Recommendation of Rigless Solution to Ensure Wellbore Integrity and Develop Low-Perm Reservoirs in Middle East: Maximize Vitality of Coiled Tubing in Staged Fracturing, Water Injection and Fluid Monitoring
Authors: Chen Chen , Haoli Bai , Shanshan Liu , Shufen Zhao , Bingshan Liu , Yang Che , Huifeng Liu 
Published: April 2024

Low-perm carbonate reservoirs in the Middle East have great potential for development. Hydraulic fracturing is one of the key technologies to unlock their commercial potential. In recent years, an increasing number of oil companies have placed emphasis on the development of low-permeability reservoirs. The Sadi reservoir in Halfaya oilfield (Iraq) is characterized as a medium-porosity, extremely low to ultra-low-permeability limestone reservoir. Due to poor reservoir properties, it has remained largely untapped. Drawing from mature experiences in developing similar reservoirs globally, the application of multi-stage hydraulic fracturing techniques in horizontal wells, exemplified by the S5H1 well, has been initiated as a pilot test. ADNOC, a decade ago, commenced the development of the Arab D tight oil reservoir. The original acid stimulation plan was modified to a fishbone fracturing completion scheme. This adjustment not only resulted in significant cost savings per well, but also achieved an initial production rate of over 2100 barrels per day, more than triple that of the original plan. The production continues to be stable at present. Besides, ADNOC has been focusing on development of low-permeability (DY Zone A), using MRC (maximum reservoir contact) and compatible reservoir stimulation technologies. In Oman's Daleel oilfield, the average thickness of the oil reservoir ranges from 10 to 30 meters, constituting a thin-layered, low-permeability carbonate reservoir.

Maintaining the integrity of the wellbore is a critical consideration in the development of low-permeability reservoirs. Poor wellbore integrity can lead to complications in the production stage, resulting in an increasing quantity of inactive strings. To mitigate potential risks, the two-barrier philosophy serves as a guiding principle. This approach mandates the implementation of two independent and tested barriers to prevent issues related to well control during production operations and interventions. Rigless solutions have proven to be cost-effective measures for enhancing wellbore integrity. Horizontal wells in the Middle East typically utilize a 6-inch open hole for completion, with some incorporating screens in the horizontal section. While this wellbore structure meets early-stage production demands, it poses challenges for later processes such as fracturing or acid fracturing. The inability to effectively segment the open hole section hinders targeted injection control and segmented production control post-stimulation.

This paper emphasizes the significance of maximizing the efficacy of coiled tubing technologies in staged fracturing, water injection, and fluid monitoring. The integration of stimulation, injection, and production control through coiled tubing is advocated to achieve staged stimulation and injection production control in barefooted horizontal sections. The sliding sleeve, a crucial component of the integrated fracturing-injection-production string, is manipulated via coiled tubing and switching tools. An intelligent water injector, propelled by preset cable packers, ensures precise water injection into corresponding layers. The downhole fluid monitoring system, relying on optical fiber, monitors bottom hole temperature, fluid production in each section, and injection profiles of each section.

Theoretical findings and successful on-site trials have proved that rigless solutions are effective to ensure wellbore integrity and develop low-perm reservoirs in Middle East, hence maximizing vitality of coiled tubing is of great importance in staged fracturing, water injection and fluid monitoring. It is recommended to deploy those technologies in Middle East in the near future.