In the high-stakes world of high-pressure gas wells, maintaining production efficiency is paramount. Yet, during workover operations, heavy mud losses can significantly impede gas flow, leading to reduced production. Refracturing has emerged as a viable solution to restore output, but the impact of heavy mud loss on this process has remained unclear—until now.
A groundbreaking study led by Yuxuan Liu from the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation at Southwest Petroleum University in Chengdu, China, sheds light on this critical issue. Published in the journal *Petroleum* (translated from the Chinese title), the research delves into how heavy mud loss during workover operations affects the refracturing process in high-pressure gas wells.
Liu and his team designed a series of experiments to simulate the conditions of heavy mud loss in artificial fractures. Using split cores to mimic initial fractures and transparent sand-filled pipes to represent sand-filled fractures, they conducted experiments under various conditions. The team employed displacement devices, CT scanning, and pressure monitoring to analyze the permeability of artificial fractures, the pressure required for repeated reconstruction, and the flow channel configuration within these fractures.
The findings are striking. “Workover heavy mud (WHM) loss has the greatest permeability damage to the proppant fracture packed with large particle size, up to 97%,” Liu explains. In contrast, fractures packed with 40/70 mesh ceramsite showed minimal damage, with permeability reduction ranging from just 0.3% to 0.7%. Slit core permeability damage was also relatively low, decreasing by 10% to 20%. However, the matrix core permeability damage measured by gas was no less than 60%, indicating significant impairment.
One of the most compelling discoveries was the dramatic increase in injection pressure before and after WHM loss, which could rise up to 80 times. CT scan results revealed that after WHM loss, nitrogen blowout and refracturing did not completely remove the pollution, leaving behind a “pollution cage” in the fracture. This “pollution cage” is identified as the primary reason for the high construction pressure during refracturing and the subsequent low production rates.
The implications of this research are profound for the energy sector. Understanding the extent of permeability damage and the factors contributing to high construction pressure can help optimize refracturing techniques, ultimately improving production efficiency and reducing costs. “Our research provides a theoretical basis for the refracturing of WHM loss wells,” Liu notes, highlighting the potential for more effective and economical solutions in the field.
As the energy industry continues to seek innovative ways to enhance production and sustainability, this study offers valuable insights that could shape future developments in high-pressure gas well management. By addressing the challenges posed by heavy mud loss, operators can better strategize their workover and refracturing operations, ensuring more consistent and higher yields from their gas wells.
For professionals in the energy sector, this research underscores the importance of continuous innovation and adaptation in the face of complex operational challenges. As Liu’s work demonstrates, a deeper understanding of the underlying mechanisms can lead to more effective solutions, ultimately benefiting both the industry and the environment.