De-blocking technology and application of high-rank CBM well in Junlian region in Sichuan Province

The coal seams of Leping Formation in Junlian area are high-rank coal reservoir with low porosity and low permeability. The gas production of some coalbed methane wells decreases rapidly in the production process, which seriously restricts the benefit development of coalbed methane wells. Combined with the production data such as drainage, hydrochemistry and pump inspection, this paper analyzes the reasons for the decline of gas production. The main reasons for the decline are coal scaling and coal fines blockage. Targeted measures such as acid pickling, hydraulic shock, plasma pulse and water injection are carried out to remove the blockage. The results show that acid pickling and plasma pulse have good effect on increasing gas production. Pickling is mainly aimed at scaling wells. By injecting acid into the wellbore and fully reacting with inorganic scale in the wellbore and near wellbore zone, the purpose of removing blockage of the passage in the wellbore and near wellbore zone is achieved. The success rate of pickling measures is high, and the input-output ratio is 1︰1.8, so it is the first choice of low-cost effective measures in the area. Pulse plugging is also aimed at coal fine output and scaling wells, and it has a good effect for increasing gas production by 130% after implementation. However, due to the limited number of implementation, the regional adaptability remains to be evaluated. The measures such as hydraulic shock and water injection are mainly aimed at wells blocked by coal fines. Coal fines are taken out to remove blockage by means of hydraulic shock and hydraulic circulation. However, such measures themselves will also cause formation stress change, which is prone to cause the negative effect. The overall effective rate of hydraulic shock and water injection measures is less than 30% and the effect of increasing production is not obvious. The above four de-blocking measures all have their own adaptive conditions, so it is necessary to take appropriate measures according to the causes of blockage to obtain the best de-blocking effect. The research results in this paper can provide some reference for de-plugging and increasing production of similar coalbed methane wells in China.