An experimental study on mitigation of oil well cement gas permeability

Permeability development within and around the cement, placed in the casing-hole annulus in oil and gas wells, is a frequently encountered worldwide problem that might lead to various adverse economic and, possibly, catastrophic consequences. The resultant loss of hydrocarbon production and, sometimes, the wells constitutes the major part of the adverse economic impact. The loss of wells, in turn, might lead to severe environmental pollution and most importantly the loss of lives. Sustained casing pressure (SCP,) described as the pressure buildup due to flow through the permeable cement matrix or the micro annulus developed around the cement, had been experienced by about sixty percent of the wells producing oil and/or gas in the Gulf of Mexico, according to the literature. Although various methods are used to prevent the problem, there is no widely accepted universal method by the industry. Currently, the problem is attempted to be mitigated using distinct methods applied either during the cementing operations or after the problem is detected. The present study is an experimental investigation for the prevention of permeability development within and around the set cement at ambient conditions. A natural magnesium complex with carbonate, coded ARI, is used the first time ever as a cement additive to achieve desired prevention. Gas permeability measurements are conducted on the samples of cements of 19 different compositions, at the end of the successive curing periods up to 28 days. ARI containing cement samples are found to develope an impermeable matrix to gas flow and to exhibit no shrinkage in volume during setting. The performance of ARI as a cement additive is also investigated in the presence of other commonly used cement additives, e.g. friction reducer and fluid loss controlling agents.