Cementing technology used in the ultra-deep wells at the LG area

The gas wells at the LG area have very complex wellbore conditions for cementing,such as large size casing cementing,long interval cementing at formations with multiple pressure systems,and production casing cementing at high-pressure gas formations,etc.In order to find solutions for those difficulties,investigation has been made on the optimization of cementing operation procedures,formulation and selection of cement slurry systems,safe casing running,selection and operation of cementing accessories,and field measures.It is concluded that:a.insertion method or double plug cementing method can be used for the 339.9 mm-diameter intermediate casing;b.reasonable slurry column and double-set loss-free rapid-hardening cement slurry can be used for the single-stage long-interval cementing of 244.5 mm-diameter casing to realize both formation isolation and gas channeling prevention;c.the double-density cementing slurry which is double-or triple-setting,H2S-resistant,rapid-hardening,right-angle thickening,and which can prevent gas channeling and lost circulation,can be used for the cementing of 177.8 mm-diameter liner where there is active gas show in the Xujiahe formation,to ensure good plugging at payzones;d.while the sand-laden and H2S-resistant cement slurry featured with high-temperature,and rapid-hardening,compound multifunction fibers can be used for the 127.0 mm-diameter liner to successfully isolate the high-pressure gas zones;and e.the low-water-loss,rapid-hardening,micro-expansion cement slurry can be used for the tie-back of 177.8 mm-diameter casing to ensure good tie-back quality.