This paper presents a case study in which microscopy was used to analyze and draw comparisons between the factors contributing to success or failure in the design of cement slurries to combat gas migration. In oilfield cementing applications, cement slurries are vulnerable to the percolation of gas up through the slurry from the producing formation. This percolation process occurs in the interval of time between the point at which the cement begins to support itself by clinging to the wellbore wall and the point at which the slurry gains enough strength to resist gas migration. In a particularly high-production gas field in east Texas, an operator experienced gas migration in wells completed early in his drilling/completion program. Since that time, other wells have been cemented without gas-migration problems. This paper presents a microscopical analysis of two different cement slurries. Included in the analysis are studies of (1) the bonding of cement to casings and wellbores and (2) peculiarities found in the formation.
展开▼
