摘要
煤层气井固井与常规天然气井固井有一定区别，前者的难点主要表现在：①低温低压下水泥浆强度发展缓慢；②水泥浆中的微颗粒对煤层割理与裂缝易造成充填与堵塞；③井壁稳定性差；④煤层属低压多压力系统剖面，地层压力系数变化规律性差，难以平衡压力固井；⑤煤层流体pH值呈酸性，易和水泥浆滤液反应产生沉淀污染储层。为提高煤层气井的固井质量，根据煤层气井的特点，确定了适用于煤层气井固井的低密度水泥浆体系的设计思路：①选择密度较低、粒径合适、抗压强度适当的减轻剂；②开发减轻剂和活性矿物微粉，利用其填充作用、级配调节作用和晶核作用来提高体系的力学性能；③选择性能良好的成膜型降失水剂和早强剂，控制水泥浆失水并提高早期强度；④确定合适的减轻剜、水泥、矿物微粉的加量比例和粒度分布，根据固井要求选定水固比配制水泥浆。据此开发出了水泥浆密度在1．20～1．50g／cm。范围内可调，水泥浆失水量低，水泥浆在25～50℃条件下早期强度发展迅速，力学性能稳定，流动性良好，施工性能良好的低密度水泥浆体系。实验结果表明，该水泥浆体系能满足煤层气井固井的要求。
Cementing in coalbed gas wells is different from that in natural gas wells.The challenges of cementing in CBM gas wells are presented herein.Besides the poor wellbore stability,(1) the slurry is slow to be set under low pressure and low temperature,(2) micro-grains inside the cement slurry may plug the cleating or fractures in the coal beds,(3) coal beds are of multiple low-pressure systems and no rules can be followed in the formation pressure variation,which will result in great difficulty in cementing under balanced pressure,and(4) coalbed fluids with a low pH value will react with the cement slurry filtrate to be precipitated,thereby,contaminating the formation.Therefore,to improve the cementing in CBM gas wells,based on the characteristics of CBM gas wells and the latest research results,the following proposals are presented for a proper low-density slurry system.(1) Such light-weight additives with low density,proper grain size,and enough compressive strength be chosen.(2) More light weight additives and active minerals be developed because their plugging effects,gradation regulation,and crystal nucleus effects can be put into use to improve the mechanical property of the system.(3) Good membrane-forming filtration reducer and early strength agents be used to control filtration and improve early strength.(4) Proper dozes and ratios of lightening agents,cement,mineral powder,and proper water-solids be determined to meet the needs of cementing operations.Such kind of cement slurry system is finally developed,with density varied between 1.20 and 1.50 g/cm3,low filtration,rapid early strength development at temperatures of 25-50 ℃,stable mechanical property,and good flowing capability.And the experiments show this system can meet the cementing requirements of CBM gas wells.
出处
《天然气工业》
EI
CAS
CSCD
北大核心
2011年第7期63-66,109,共4页
Natural Gas Industry
基金
国家科技重大专项"煤层气筛管
洞穴
裸眼等完井技术研究"(编号:2008ZX05037-001)
关键词
煤层气
固井
紧密堆积
低密度水泥
钻井液
粒径
减轻剂
增强材料
coalbed methane,cementing,close packing,light weight cement slurry,drilling fluid,grain size,lightening agent,reinforcing material
