Enhancing Reservoir Productivity in Carbonate Formations Propped vs Acid Fracturing Strategies at Lekhwair Area
Authors: Al Malki Z. , Al Manthari M. , Al Aamri A. , Al Farsi A. A. , Al Wahaibi A. A. , Salleh P. , Al Bahri K. H. , Al Mahrouqi A. , Al Wahaybi M. , Christiawan A. , Yuyan Rioka 
Published: February 2024

This paper represents a follow-up to a previous hydraulic study conducted in the same area, with the inclusion of acid fracturing treatment execution and evaluation to conclude a comprehensive comparison study with the earlier propped fracturing campaign.

In the Lekhwair satellite fields, the reservoir properties of Cretaceous carbonate formations (Natih C1 and Shuaiba) oil reservoirs were found to exhibit lower mobility than initially projected. In response, post-drilling matrix stimulation was performed using 20% HCl, albeit with limited success.

To address these challenges, we initiated a hydraulic fracturing study aimed at assessing the response of these tight permeability carbonate rocks to stimulation. An integrated multidisciplinary approach was developed to compare the design of propped fracturing and acid fracturing treatments in carbonate settings. This approach involved the integration of acoustic borehole imaging data, geomechanical analysis, petrophysical logs, mineralogy, and other factors to optimize the design. A range of well candidates, including oil producers and water injection wells, with both vertical and highly deviated cased hole completions and open-hole horizontal wells, were selected.

During the candidate selection process, the primary challenge in carbonate formations was to ensure that the design contained the fracture height and half-length within optimal parameters. This was crucial to prevent lateral uncontrolled fracture propagation towards nearby water injection wells and producers, as well as to safeguard the integrity of the cap rock (natural barrier) within the carbonate setting. The study also compared post-fracture well performance between propped fracturing and acid fracturing, utilizing advanced technologies such as self-consolidated proppant, retarded emulsified acid, and degradable particulate diverters.

Prior to the fracture treatment, the selected wells had minimal production due to poor inflow, resulting in very low gross and net oil production. These wells were operated on an ON/OFF schedule to manage reservoir pressure and address issues with Electric Submersible Pump (ESP) reliability caused by the extremely low flow rates. Post-fracture well treatment results indicated a significant improvement in gross and net oil production, with production increasing by up to 20-fold, and the ESP lifetime extended in comparison to the pre-fracture period. These wells could now operate continuously within the optimal ESP operating range and were no longer subject to ON/OFF scheduling. The uptime of these wells improved from 25% to 100%.

Notably, this paper serves as a sequel to a previous hydraulic study, with a focus on the inclusion of acid fracturing. The results of this study contribute to a comprehensive comparison of acid fracturing method on this carbonate reservoir, with the earlier propped fracturing campaign. Even though several treatment fluid system has been studied, including linear and cross-linked gel acid, retarded emulsified acid system for acid fracturing and borate cross-linked guar fluid for propped fracturing, the main intention of this paper is rather to concentrate on method comparison than fluid discussion, therefore the section covering the laboratory and fluid discussion is limited to critical design related information. The findings represent a significant step forward in the understanding of stimulation techniques in carbonate formations and offer valuable insights for future field development plans. In conclusion, this study builds upon previous research, offering a deeper understanding of hydraulic fracturing techniques in carbonate formations and providing valuable insights for some novel technologies advancement.