Solutions to Difficulties Met in Gas Well Cementing in Block Anaco (Venezuela)
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摘要: 委内瑞拉ANACO区块地层破裂压力梯度低,有高压水层和低压气层,环空容易发生气窜,并含有H2S和CO2,呈泥质砂岩。基于以上认识,ANACO区块固井的复杂性主要源于水泥基材料固有的缺陷和地层条件的多变性,正确认识地质条件对固井的影响和选择合适的固井材料、工艺措施是解决固井难题的基本出发点。针对该地区地质因素,从分级注水泥、双密度或多密度水泥浆体系工艺上、水泥浆及外加剂选择等方面进行了研究;同时结合现场固井状况进行了对策方案归纳,并对腐蚀深度和防气窜性能进行实验探索。结果表明,研发的防窜防腐蚀水泥浆最低密度为1.2 g/cm3,且上下密度差低于0.03 g/cm3,游离液接近0,抗压强度高,渗透率低;通过引入防腐蚀材料BCE-750S后,硅酸盐水泥石在7、30和60 d的腐蚀深度大大降低,能够解决当地环空气窜、含有H2S和CO2酸性气体等问题。Abstract: 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.
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Key words:
- Low density cement slurry /
- Stage cementing /
- Gas channeling in annulus /
- Well cementing /
- Venezuela
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