A new model and application of coalbed methane high efficiency production from broken soft and low permeable coal seam by roof strata-in horizontal well and staged hydraulic fracture

ZHANG Qun; GE Chungui; LI Wei; JIANG Zaibing; CHEN Jiaxiang; LI Bingang; WU Jianguo; WU Xiuping; LIU Jia

doi:10.13225/j.cnki.jccs.2017.1422

Abstract：Coalbed methane high efficiency production from broken soft and low permeable coal seams has been being a technical bottleneck of restricting coalbed methane industrialization development and coal mine gas control for many years.This paper has investigated the No.8 broken soft and low permeable coal seam in Lulling coal mine of Huaibei mining area in Anhui Province,China.Site investigation,sampling and testing,theoretical analysis,hydraulic fracture physical and numerical simulation have been performed.As a result,a new model of coalbed methane high efficiency production from broken soft and low permeable coal seam by roof strata-in horizontal well and staged hydraulic fracture has been presented,the hydraulic fracture extension and control mechanism under this model have been revealed,and the main technological processes of the model implementation have been given.The results show that the roof strata are relatively brittle and have high propagation pressures,while the broken soft coal seam is relatively plastic and has a low propagation pressure.When case perforation and hydraulic fracture are performed in horizontal well of the roof strata,the hydraulic fractures in roof strata,on the vertical,extend downward and penetrate the broken soft coal seam.At the same time,the hydraulic fractures also get rapid horizontal extension,and the traction engendered by this rapid horizontal extension rips the coal seam to form long hydraulic fractures in the coal seam.Numerical simulation results show that the hydraulic fracture length formed in the broken soft and low permeable coal seam when fracturing in roof strata is long as 6.7 times as that when fracturing directly in the coal seam.Those hydraulic fractures formed in the roof strata and the broken soft coal seam are filled with sand proppant in follow-up adding-sand fracturing,and come into being a coalbed methane migration pathway from the underlying coal seam to the roof strata-in horizontal well.It can be seen that broken soft coal seam can get a good fracturing stimulation effect in this new model.The results of this study are applied to the coalbed methane development demonstration project by roof strata-in horizontal well and staged hydraulic fracture in Luling coal mine of Huaibei nining area in Anhui province,China and have obtained a good gas production effect.The average daily gas production rate of the single coalbed methane horizontal well was respectively 10358 m3,9039 m3,7921 m3 in three,six and twelve consecutive months.As of November,16,2017,this horizontal well already produced 5 million cubic meters of coalbed methane gas,and its daily gas production rate was still over 3200 m3.This has created a new record of gas production of a single coalbed methane horizontal well from broken soft and low permeable coal seam in China.