Effective Matrix Stimulation of Limestone Streaks in a Predominately Shale Formation Using VES Diverter Acid Reinforced with Clay/Shale Stabilizers Led to 300% Increase in Gas Production
Authors: Saeed Muhammad Salman , Elmoneim Hossam A. , Yousuf Arif , Shahzad Kamil , Anwar Rameez , Abdulqader Mustafa S. , Khokhar Saad Y. , Imran Muhammad 
Published: November 2024

Matrix stimulation is widely used for removing near wellbore damage and optimizing production from a wellbore. Understanding of the reservoir characteristics and properties plays a key role in the success of a matrix stimulation treatment. Embracing the challenges posed by heterogeneity of reservoir formation is critical to devising a strategy for the matrix stimulation treatment. Matrix stimulation treatments are performed in limestone and sandstone formations, while hydraulic fracturing is employed in shale reservoirs. The selection of treatment becomes a challenge in shale formations containing streaks of hydrocarbon bearing limestones. This paper discusses in detail the successful planning and application of matrix stimulation in such shale formation.

The Ghazij formation is predominately a shale formation. However, in the region of the field under consideration it contains multiple streaks of fractured limestone. Drilling of the first well in 2019 confirmed the presence of hydrocarbons (dry gas) in these limestone streaks. An appraisal well was drilled in 2022 as part of field development plan. During drilling, losses were observed in the pay zone. Pressure transient analysis and open hole logging confirmed deep damage in the limestone streaks. Multiple connected fractures were also identified during log interpretation. SWT was performed to determine reservoir potential. Initial flow from the reservoir and corresponding FWHP was not promising. Hence, matrix stimulation was necessary to remove the near wellbore damage. Pertaining to the presence of shale beds along the limestone streaks, matrix stimulation posed multiple challenges. The presence of connected fractures in the limestone streaks further complicated the job design. It was necessary to avoid diversion of acid towards the shale beds. Furthermore, acid recipe must be reinforced with additives to minimize disturbance of shale. Hence, matrix stimulation treatment was designed with a new clay/shale inhibiting solution and viscoelastic diverter-based acid system.

Focused jetting of treatment fluids using coiled tubing's cyclic movement was performed in front of the perforated intervals. Indication of diversion of treatment fluid was observed on surface. Prior to matrix stimulation treatment, the well was producing 3.2 MMSCFD of gas. Posttreatment after completion of cleanup, well was flowing at 12.9 MMSCFD of gas rate (same choke size). This corresponded to more than 300% improvement in flow rate. Considerable improvement in WHFP was also observed. WHFP increased from 270 psi to 1050 psi at same choke.

This paper illustrates the strategy for designing and executing matrix stimulation treatment of hydrocarbon containing limestone streaks in a predominately shale formation. This type of stimulation technique was the first of its kind, employed for production optimization of shale formation. The results of this matrix stimulation strategy were exceptional, and it can be referred to while dealing with similar challenges.