Hydraulic fracturing in the tight sandstone of the KS Field has been implemented in more than 200 wells since 2002. Year by year, it gets more challenging due to limited well candidates with good properties and a decreasing trend in production result. Thus, hydraulic fracturing optimization both in design and execution are critical to increase success ratio and to contribute more oil production. One of the efforts is delivering fit-to-purpose design through fracture height growth identification and mitigation.
A mechanical earth model (MEM) is constructed to obtain elastic properties and stress profile as an input for fracture geometry simulation as a preliminary tool for height growth prediction. The MEM is generated using triple combo and sonic logs and validated with wellbore stability analysis. A pre-treatment mini-frac was performed and analyzed before the main fracturing operation to calibrate and update the MEM stress profile. For final validation, the profiles of MEM, MEM optimized fracture simulation and temperature log results are compared to evaluate the fracture height growth issue. Last, fit-for-purpose strategies are applied to optimize the fracture geometry result and maximize oil production.
Previously, hydraulic fracturing with high proppant volume has been used to create long fracture half-length providing large reservoir contact and thus improved productivity. Unfortunately, production after fracturing in some wells shows no significant change and occasionally yields high water cut. Currently, detailed pre-fracturing evaluation is applied. Comparison plot results show fracture growth consistency between the MEM-optimized hydraulic fracturing simulation with temperature log profiles, validating the suspicion of fracture height growth to and through the upper and lower barriers of the fracturing target.
Two design changes were then proposed to control fracture height growth: Applying lower-viscosity fracturing fluid by decreasing gel loading or changing to viscoelastic surfactant fluid; and applying an artificial barrier technique. These changes are designed to reduce fracture height growth and increase effective fracture half-length in the pay zone. The result is increasing fracturing success ratio, from 40% to 70%, which contributes to arresting the production decline of the KS Field.
Integrating geomechanics analysis (in the form of MEM) into hydraulic fracturing design simulation and profile comparison, MEM-optimized hydraulic fracturing simulation and temperature logs have validated the issue of fracture height growth problems in the KS Field and justified the application of fit-for-purpose strategies to mitigate the issue.