Three different techniques are presented for detection of the presence and severity of off-balance fracture growth. These are statistical analysis of total friction pressure during mini-fracs, analysis of mini-frac shut-in data, and statistical analysis of main treatment pressures. Most treatments allow application of all these techniques, which will increase the level of confidence in the analysis. All these techniques rely mainly on changes in treatment pressure, not its absolute value. This makes them very suitable for analysis of majority of industrial hydraulic fractures.
Off-balance growth can result in breakage of the bond between the casing and formation. This condition is defined as pseudo-openhole and usually facilitates a better linkage between the wellbore and the dominant fracture, thus reducing the severity of off-balance growth.
Analysis of fracturing pressures has been the subject of much research and technical presentations within the oil and gas industry. Fracturing is an essential part of productivity enhancement. Treatment analysis is essential to understanding and improving the quality of fracturing. Pressure is the main independent response of the formation to fracturing.
Early analysis techniques used very simplified single fracture models to relate changes in fracturing pressure to the mechanical properties of fracturing fluid and the formation, as well as the shape of the fracture (Perkins and Kern1, Khristianovich and Zheltov2). It was soon recognized that actual hydraulic fracture behavior is too complex to be represented by simple models. Building on Perkins and Kern fracture model, Nolte and Smith3 offered techniques that related changes in fracturing pressure to the mode of fracture growth; whether confined, unconfined, screenout, etc. Additional factors such as near-wellbore tortuosity (Aud et al4) and perforation phasing and near wellbore multiple fracturing (Stadulis5) were offered to explain unusual fracture behavior and screenouts. All of these models were still based on the concept of a single dominant fracture extending at points outside of the near-wellbore region.
The path and behavior of hydraulic fractures is too complex to be modeled by simple growth concepts. The treatment often causes changes in the wellbore and its completion details that in turn affect itself. These changes are too unpredictable to lend themselves to simple modeling. For these reasons this paper offers a combination of different techniques for understanding the growth pattern of hydraulic fractures. These consist of a statistical analysis of fracturing pressures as well as observing pressure decline pattern during fracture closure.