Natural Gas Geoscience ›› 2021, Vol. 32 ›› Issue (4): 465-471.doi: 10.11764/j.issn.1672-1926.2020.10.006

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Productivity prediction of vertical test well for fractured coal reservoir under hydraulic fracturing

Zhi-rong WANG(),Zhen-yang WEN,Ling-xia CHEN   

  1. School of Hydraulic Science and Engineering,Zhengzhou University,Zhengzhou 450001,China
  • Received:2020-08-28 Revised:2020-09-28 Online:2021-04-10 Published:2021-04-09
  • Supported by:
    The National Natural Science Foundation of China(41272339);the Natural Science Foundation of Henan Province, China(182300410149)

Abstract:

Production capacity prediction of CBM is a difficult technical problem that the natural gas industry tries to solve. In order to explore the permeability mechanism and productivity rule of fractured CBM reservoirs in the "three soft" coking mining area under the condition of hydraulic fracturing, firstly, the influence of geometric characteristics of primary fractures on fracture growth rule was considered, and an improved hydraulic fracture growth model was established in combination with the classical PKN model; secondly, a reservoir dynamic permeability model was established based on the dynamic equation of reservoir pressure gradient, considering the influence of the geometric size change of hydraulic fractures on the porosity of primary fractures in coal during drainage and production; finally, based on the principle of fluid mass conservation, the productivity prediction model of CBM vertical wells in fractured reservoirs was established. This model was used to calculate the production capacity of Well GW-008 during the trial period of 70 days in the mining area, and it was compared with the actual discharge and production value. It was founded that the dynamic change curve of the theoretical calculation value and the actual discharge and production value was in good agreement with each other. The average daily gas output is 360.768 m3/d and 381.489 m3/d respectively, and the relative error is only 6%, thus verifying the correctness of the production capacity model. The research results are of great significance to the development and utilization of coalbed methane in the “three soft” areas of China.

Key words: Native fissure, Hydraulic fracturing, Dynamic permeability, Productivity model

CLC Number: 

  • TE32

Fig. 1

Fracture propagation model"

Table 1

Fracturing parameters of Well GW test-008"

参数数值
煤层深度/m583.50
煤层厚度/m7.01
施工排量/(m3/min)7.60
时间/min50
压裂液/m3前置液200.00
携砂液204.00
替置液5.80
压裂液总量409.80
平均砂比/%18.20
施工压力/MPa破裂压力9.80
停泵压力6.60

Fig.2

Dynamic change curve of permeability of Well GW test-008"

Fig.3

Comparison of measured and theoretical gas production values of Well GW test -008"

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