Understanding the Key Factors Affecting Well Integrity in Horizontal Well Multistage Hydraulic Fracturing

With the significant increase in multistage hydraulic fracturing in the last two decades, occurrence of casing failures has also become noticeable, raising wellbore integrity concerns among operators worldwide. The consequences of casing failures can be varied, but in many cases they affect well production, wellbore accessibility, and, in some rare instances, present well control and associated risks. In fact, tubular damage during fracturing is not caused by a single, consistent reason. Rather, it varies greatly across the industry. Investigators have identified several different factors that come into play when identifying tubular fatigue failure when exposed to high stress loads during pressure and temperature cycles in a multistage fracturing operation. Other contributing factors are well trajectory and borehole inclination with respect to the fracture plane, the quality of the cement bond, the development of "trapped pressures," or change in in-situ stresses that could initiate formation movement. A parametric study was conducted using worldwide data to evaluate and determine the main factors controlling overall well integrity. Casing failure was defined as a reduction in the internal diameter of the pipe from its initial completion state before hydraulic fracturing. The failure events were studied and compared with the same factors in successful wells. This paper provides an insight into the relationship between borehole condition (primarily hole size), well deviation, well azimuth, dogleg severity, pipe centralization, the type of hydraulic fracturing treatment performed (i.e., proppant frac or acid frac) and the risk of pipe deformation. By understanding the primary factors that affect well integrity, the likelihood of casing failure can be predicted and avoided ahead of time, save fracturing costs across high-risk areas, and not jeopardize production from multimillion dollar completions. Managing well integrity is essential for development of oil and gas resources while preserving the environment and assuring safety of personnel.