Long-Term Mechanical Properties of Barrier Materials for Cementing Operations – Analysis of Morphology and Micro-Structure

In the oil and gas and geothermal industry, a barrier material is pumped behind the casing to fill the annular gap between the casing and formation/outer casing. After placement, this slurry is solidified rapidly, and it functions to seal the annular space and protects the casing during the lifecycle of the well. In this article, four different barrier materials namely expansive cement, non-cement pozzolan-based material, geopolymer, and thermosetting resin are examined under equal conditions. The long-term mechanical properties of the candidate materials were tested by measuring uniaxial compressive strength (UCS), tensile strength, and Young’s modulus. These properties were measured at seven different time intervals, from one day to nine months after curing at a bottomhole static temperature of 90 °C and pressure of 170 bars. The change in the mechanical properties was further investigated by using scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques. The results were benchmarked with the properties of the API neat class G cement as non-commercial reference material. Our results show that the neat class G cement had a consistent behavior in most of the test period, and its UCS was dropped by 23 % after nine months compared to six months. The expansive cement had no significant change in mechanical properties, but the expansive crystal can weaken the structure, especially close to the boundaries with the cement matrix. The pozzolanic material and geopolymer did not develop early strength. The pozzolanic material reached a plateau after seven days, while the geopolymer developed strength up to six months. The thermosetting resin had the highest UCS and tensile strength up to one month, but its mechanical properties were started to deteriorate from seven days after curing.