Solutions to Difficulties Met in Gas Well Cementing in Block Anaco (Venezuela)

Drilling in the Block Anaco,Venezuela has encountered downhole problems such as low formation fracturing pressure gradient,high pressurized formation water and low pressure gas zones,as well as gas channeling in annulus,often accompanied by H₂S and CO₂.Lithology of formations where these problems have been met is argillaceous sandstone.It has been ascertained that troubles met in the cementing operations in this block come from cement and the variety of formation conditions.Solutions to these problems lie in the correct understanding of the effects of geological conditions on well cementing and selection of proper cementing materials and technology.Studies on stage cementing,dual-density or multi-density cement slurries and the selection cementing additives have been conducted.Experiments on corrosion depth and gas channeling prevention have been done.The studies and experiments reveal that the minimum density for anti-channeling anti-corrosion cement slurry is 1.2 g/cm³,and the density difference between the top and bottom of the cement column shall not be greater than 0.03 g/cm³.Free water should be near 0,and the set cement should have high compressive strength and low permeability.Use of corrosion inhibitor BCE-750S in cement slurry of common silicate cement greatly reduced the 7 d,30 d and 60 d corrosion depths in the set cement,solving the gas channeling in annulus and H₂S/CO₂ problems in the Block Anaco.