Degradable Materials Comprehensive Testing Provides Valuable Insights for Multistage Fracturing Completion System Applications in HPHT Wells

Degradable technology has been used in Multi-Stage Fracturing (MSF) operations since early 2000. The efficiency gained from utilization and availability of a wide variety of degradable materials has accelerated its adoption in the oil and gas industry. MSF applications, such as ball drop MSF frac sleeves or plug and perf stimulation are the most prevalent practices where degradable technologies are utilized. The understanding of the degradation mechanism and factors affecting the same are paramount in material selection and operational planning. With real-well scenarios and extensive lab testing, this paper aims to comprehend the challenges in the utilization of dissolvable frac balls and proposes adequate solutions. In the context of this paper, terms "degradable" and "dissolvable" are used interchangeably, as is normal in the industry. And the focus will be on dissolvable metallic alloy frac balls which is magnesium based, although the behavior of other metal-based alloys is fairly similar. Fundamentally, all degradable products operate on a similar mechanism – a chemical reaction with water which produces a microscale powder as a byproduct. Ball drop frac sleeves utilized in MSF completion systems have been a proven method to improve operational efficiency. The utilization of dissolvable balls has simplified operations by reducing wireline or Coiled Tubing (CT) interventions. Nevertheless, in deep gas wells, MSF system components have to stand for higher differential pressures and temperatures. Dissolution mechanisms largely depend on the downhole temperature, amount of water in contact with the dissolvable ball, and the fluid salinity. The results underscored the importance of analyzing well parameters and fluid properties accurately to obtain predictable behavior from dissolvable frac balls utilized in MSF completion systems. The key observations related to medium, fluid contact, dissolution mechanisms, engagement of frac ball with ball seat will be elaborated, which can be implemented for improving fracturing operational performance in High Pressure High Temperature (HPHT) wells. These observations were then correlated with lab tests in representative fluids and temperatures, which served to confirm the hypotheses. In addition, the sealing properties of these balls along with their interface with ball seat have also been explored with a view to understanding an optimum method to be employed in operations. Dissolvable technologies for MSF, while extremely efficient and useful to simplify and accelerate frac operations, is not an exact science. The benefits from utilization of this technology, however, far outweigh the potential uncertainties. The uncertainties can further be reduced by understanding the environment of operation and planning for viability and dissolution times accordingly. Further, availability of contingency measures and forward planning will greatly enable the advantages of utilizing a completion system focused on degradable material performance.