HPHT Refracturing in Tight Cambro-Ordovician Sandstone Gas Reservoirs: Strategies, Challenges, and Lessons Learned

Abstract This paper presents key lessons learned from the full cycle of refracturing design, execution strategies, and post-treatment evaluation in deep High Pressure High Temperature (HPHT) tight rock reservoirs. The study is based on fracturing treatments in three wells, each initiated under different justifications—one involving immediate refracturing due to premature, incomplete fracture placement, and the others conducted post-depletion of the initial fractures. Insights from these cases provide a comprehensive understanding of refracturing effectiveness in complex HPHT environments. The Haima Supergroup in the Abu Butabul Fields is a Cambro-Ordovician tight gas sandstone reservoir, positioned in the Southwestern area of the Fahud Basin, along the local North-South trend of Western Deformation Front. Hydraulic fracturing is essential for completion and production from these formations. The field comprises two primary reservoirs within the Haima Supergroup, Barik and Miqrat, both consisting of multiple layers at vertical depths of 4,000 to 5,000 meters. These HPHT conditions pose significant challenges for hydraulic propped fracturing, especially refracturing. Despite their shared HPHT nature, they exhibit distinct geomechanical characteristics, requiring different refracturing approaches. Miqrat consists of shaly sand layers with indications of pore pressure communication, lacking a distinct geomechanical barrier. Barik comprises four thin isolated sand layers, separated by competent shale, exhibiting pressure and stress contrasts. Reservoir temperatures up to 300 degF, with pore pressures between 6,000 and 8,500 psi across different layers. These variations result in minimum horizontal stress contrasts of 9,000 to 11,000 psi, with anticipated fracturing treatment pressures reaching up to 13,500 psi at the top design rate. A joint task subsurface team has compiled a pool of over 40 potential candidates for refracturing. Following a detailed ranking process based on technical and economic criteria, the final selected candidate wells have been scheduled for execution in accordance with the agreed business plan. Two of the subject wells were selected for refracturing after several years of production, requiring evaluation of remaining reserves, depletion-altered geomechanics, and residual stress shadow effects from the initial fractures. These factors were critical in optimizing the refracturing design. The third well underwent immediate refracturing following an incomplete initial fracture placement due to operational issues. In this case, diagnostics of the initial fracture geometry, stress anisotropy, and stress shadow effects played a crucial role in refining the refracturing approach. Refracturing treatments successfully placed the designed proppant volume into the target intervals, demonstrating the effectiveness of the methodology. The success was attributed to a holistic approach, incorporating, selective interval reperforation, stress conditioning fracture methodology, optimized fluid rheology and pumping schedules, prefracture diagnostics using temperature and tracer measurements. Post-refracturing flowback tests showed significantly improved performance compared to the initial fracturing treatments, confirming the effectiveness of the refracturing strategy and the achievement of the intended objectives. Notably, this paper provides new insights into the feasibility of refracturing HPHT Cambro-Ordovician formations along the edge of Western Deformation Front, an approach that has previously been underexplored from both technical and economic perspectives. The lessons learned have been consolidated into a best practices framework, serving as a guideline for future operations and optimization strategies.