Optimize flowback operations and production in an unconventional reservoir

An important stage between the end of fracture treatment and the beginning of production is the flowback period. It usually involves high rates of drawdown imposed on the well to accelerate fracture fluid unloading, sand cleanup, and hydrocarbon production. If the flowback operation is not properly performed—taking into account rock and fluid properties—damage can be done to the formation, the fractures, or both. In this context, excessive proppant flowback from fractures presents a significant concern because it usually results in the creation of unpropped areas in the near-wellbore zone, which can easily be pinched closed later in the life of the well, leading to loss of the connection between the wellbore and the fracture.

While completing wells in the oil-rich Bone Spring sand in the Delaware basin, Devon Energy wanted to optimize flowback operations and mitigate potential fracture connection loss by minimizing the risk of uncontrolled sand flowback and near-wellbore fracture pinchout.

Integrate well and geomechanics data into advanced poststimulation flowback design

Schlumberger worked with Devon Energy to deploy AvantGuard advanced flowback services to develop a customized predictive flowback strategy based on choke management. Comprehensive well testing data, including high-frequency fluid rates, sand rates, wellhead pressure, and solids and water samples, were gathered and analyzed for two of the operator's wells in the basin.

The team proposed using the SOE approach to ensure preservation of connectivity between the hydraulic fractures and the wellbore during the lifetime of the well. The analysis revealed the following conclusions for the flowback operations conducted in Well 1:

• insufficient effective stress on the proppant was applied at the beginning of the flowback operations
• flow rates exceeded the limit for proppant pack stability at 2,000 bbl/d
• rates were reached beyond the recommended SOE to create unpropped cavities near the wellbore
• expected loss of fracture connectivity at bottomhole pressure less than 3,250 psi was due to closure of unpropped cavities, in turn limiting production performance

AvantGuard Observe flowback transient monitoring and analysis was used for real-time monitoring of flowback operations in Well 1, including the collection of samples of produced solids and liquids. Laboratory analysis identified that the solids returned to surface were proppant, and later samples contained smaller-size particles compared with earlier-acquired samples, indicating a certain degree of proppant crushing. These data were integrated in the design basis to propose a less aggressive flowback strategy that considered formation and fracturing design variables and changes in the proppant type to mitigate crushing potential for the subsequent wells.

Continuous solids monitoring by AvantGuard Observe monitoring and analysis detected changes in solids production over time. The trend on the solids rate indicated an increase in continuous solids production at flow rates greater than 2,000 bbl/d, correlating with the SOE predictions. Further analysis of the SOE indicated that the maximum production rate of 3,580 bbl/min should result in the creation of unpropped zones, which may cause pinchout later during the lifetime of the well at a bottomhole pressure of 3,250 psi. This conclusion was later confirmed by rate transient analysis after a decrease occurred in the bottomhole pressure below the predicted level.