Early-age compressive strength assessment of oil well class G cement due to borehole pressure and temperature changes

Development of high early-age compressive strength oil well cement is an important task in the oil well cement design. Achievement of suitable early-age compressive strength of oil well cement ensures both the structural support for the casing and hydraulic/mechanical isolation of borehole intervals. Holding this issue in mind, in this research, the effect of pressure and temperature changes inside the borehole on the class G oil well cement compressive strength has been studied. In the proposed work, in contrast to the mostly previous studies which considered some certain temperatures and atmospheric pressure in their tests, the effects of contemporary pressure and temperature changes on the early-age compressive strength of oil well cement have been investigated. Using a non-destructive method, the compressive strength of 48 hours cured cement samples under progressive changing of simultaneously pressures and temperatures coincident to a real oil well data were measured and recorded continuously at predefined intervals during this 48 hours period time. The case study was an oil well located in Darquain region of Khuzestan province in Iran. Obtained results showed that 8 and 12 hours aged samples have a maximum compressive strength in a certain combination of pressure and temperature, 51.7 MPa and 121°C, whereas 24, 45 and 48 hours aged samples have a minimum point in their compressive strength curve at 17.2 MPa and 68°C and a maximum point at 41.4 MPa and 82°C. All the samples show the significant reduce (up to approximately 70%) in compressive strength after the 51.7 MPa and 121°C point. Considering the case study oil well profile of borehole pressure and temperature changes, this tested class G cement is recommended to use in cementing job from ground level down to the almost 4000 m below the surface. (Journal of American Science 2010;6(7):38-47). (ISSN: 1545-1003).