Containment of a Vertical Tensile Region During Surfactant-Polymer Injection

Many studies have been completed concerning the evaluation of fracture height growth during hydraulic fracturing. While there are analytical solutions available to estimate vertical fracture growth, a more comprehensive solution requires the use of coupled geomechanics-reservoir simulators that could also fully incorporate the effects of fluid-flow into the analysis. This paper introduces results from a new coupled in-house geomechanical/ reservoir simulator to estimate the extent of vertical tensile regions developed in the sand interval that could break into adjacent shales during surfactant-polymer injection for a well located onshore Asia. The reservoir was treated as an elastic material and the injection zone was treated as a zone of higher permeability after the weakly consolidated formation reached a tensile stress state. The geomechanical information for the simulator was obtained from triaxial tests, well-logs and minifracs. Reservoir and fluid data were extracted from the in-house reservoir simulator model available for the field. A highly conductive network of microfractures is modelled for that cell using a permeability multiplier function, PMULT. A half unit of a seven-spot pattern was evaluated by using an unstructured grid, which provided more geometric flexibility. The results indicated that injection rates higher than 4,000 B/D (0.0074 m 3 /s) combined with viscosities greater than 10 cp (0.01 Pa-s) will cause the fracture to break into the shales penetrating into the bottom sand. On the other hand, injection rates lower than 2,000 B/D (0.0037 m 3 /s) were shown to be safe, even for the highest viscosity injection fluid tested, viz 30 cp (0.03 Pa-s). Viscosities greater than 20 cp (0.02 Pa-s) cause the injection fluid to break into adjacent sands if flow rates are above 2,000 B/D (0.0037 m 3 /s). As expected, the higher the viscosity and injection rate, the higher the tendency of the fractures to grow out of containment. A chart with safe limits for surfactant-polymer injection was provided to the business unit to guide them in the design of new injectors and provide safe conditions for surfactant-polymer injection.