Abstract: To address the issues of excessive water consumption,high production decline and insufficient fracture extension during deep coalbed methane(CBM)development in the Daji Block of the Ordos Basin,a pre-CO₂ foam fracturing process for CBM was developed.Through rheological analysis,foam stability evaluation fracturing fluid formulation tests,a guar-gum/polymer gel CO₂ foam fracturing fluid system was established.Experiments showed that under simulated reservoir temperature and pressure,foam quality between 82% and 85% and half-life greater than 250 min achieved,which providing high foam stability,low formation damage,and strong sand-carrying capacity.Based on CO₂ abilities to enhance energy and promote fracturing and to displace and desorb methane,a combined process of pre-CO₂ foam energy enhancement plus high-proppant fracturing with a high sand volume guar gum/polymer system was innovatively proposed.Using a co-injected diverting sand and staged sand ramping mode,the first deep CBM pre-CO₂ foam fracturing was implemented in the Jishen X-7 well in the Daji Block,which achieved a maximum sand ratio of 38%(average 28%)-a record.The results showed that this process increased daily production by 75% compared to guar-gum fracturing wells,reduced fracturing water use by 34% versus conventional wells,increased fracture network complexity by 8%,and which resulted in a stabilized post-fracturing production period with daily gas output of 7×10⁴ m³ and stabilized casing pressure rising to over 1.2 times initial.The successes in increasing production and reducing water indicate that the pre-CO₂ foam fracturing technology is a new approach for green,efficient development of deep CBM.

Key words: reservoir stimulation, foam fracturing, pre-CO₂ fracturing, guar-gum fracturing, deep coalbed methane