Overcoming the Challenges in Hydraulic Fracturing

Hydraulic-fracture modeling relies heavily on the prediction of fracture geometries. The geometry of the fractures will determine the flow of water and oil through the rock, which is essential for predicting the success of a fracking operation.

FREMONT, CA: The development of theoretical hydraulic-fracturing models began several decades ago, establishing the foundation for hydraulic-fracturing design, optimization, and diagnostics. Hydraulic fracturing stimulates reservoirs by predicting the geometric shape and dimensions of the growing fracture over time. An integrodifferential equation with moving boundaries solved numerically over many steps corresponds to this mathematical representation.

The following are certain challenges associated with multifracture modeling from horizontal well operations. It will be possible to create more realistic models by using simulation techniques to facilitate the simulation of these common occurrences, despite each formation presenting its own challenges.

Nonsimultaneous fracture initiation within a stage: The fracture propagation pressure is significantly less than the fracture initiation pressure in a given rock. It is more beneficial for the fracturing fluid to enter an existing fracture and propagate it instead of initiating new fractures from nearby perforations when fractures start earlier from one perforation.

Dominant fracture creation: Dominant Fractures have a much larger growth than those that are not dominant. When the fluid was pumped from a single source for more than one fracture, dominating fractures were a consistent result. Acoustic sensing data from the field-scale operations support this observation qualitatively. A dominant fracture receives all the fracturing fluid at the end of a stage while the remaining fractures stop propagating. These few dominant fractures contributed significantly to the post-stimulation well productivity.

Inactive perforation clusters: It is possible for fractures to occur downstream from perforation clusters if fracture fluid bypasses the entire cluster. A perforation cluster may be inactive between two active clusters or adjacent to two active clusters.

Several factors may contribute to nonsimultaneous fracture initiation and dominant fracture creation when a perforation cluster fails to generate fractures. Muiners can eliminate inactive perforation clusters using limited-entry techniques that use varying perforation numbers and diameters, which can minimize interference between fractures from horizontal wells growing simultaneously.

Fracture reorientation in the near-wellbore region: Well drilling disturbs the surrounding stress field in a way that can alter the fracture plane compared to what would be dictated by the far-field stress state. Fractures occurring within the near-wellbore region or those propagating away from the near-wellbore region terminate prematurely.

Complex fracture networks near wellbores can cause fluid flow resistance, resulting in completion and production problems such as early screenouts and low post-stimulation well productivity.