Multi-branched horizontal wells for coalbed methane production: Field performance and well structure analysis

• CBM Field production data from fractured vertical wells and horizontal wells.
• Reservoir simulation and well models for productivity prediction of CBM wells.
• The mechanism and advantages of multi-branch horizontal wells.
• The drainage volume of different horizontal wells.
• Sensitivity study of well’s structure on MBHWs’ productivity.

Horizontal wells, such as multi-lateral and multi-branched horizontal wells (MBHWs) have been effectively used in the development of coalbed methane (CBM) fields, especially for coal beds with very low permeability and low compressive strength, in which the performance of conventional fracture-stimulated vertical wells is ineffective. In this study, the performance of MBHWs in the Liulin block of the Ordos Basin in central North China is analyzed and compared to that of hydraulically fractured vertical wells. The field pilot data show that the gas production rate of most fractured vertical wells decreased rapidly after a short period of time, far below expectation, while the performance of MBHWs is satisfactory and relatively stable during 3 years of production. A numerical simulation model was established based on the coal reservoir characteristics. The productivities of different well types are predicted and compared to the field data. The poor performance of the fractured vertical wells is thought to be caused by the early closure of the fractures and proppant embedded in the coal matrix or by a poor proppant delivery inside the fractures. The high and stable productivity of the MBHWs is attributed to their large drainage volume and to the stability of the wellbores. Simulation results show that the parameters of a MBHW, such as the branch angle, length, and spacing, can be optimized to maximize its productivity. Though the drilling cost of a MBHW is relatively high in comparison to vertical wells, its high and stable productivity can compensate for the drilling cost. Therefore, MBHWs are thought to be more appropriate than vertical wells for the successful exploitation of the CBM resource potential in the Liulin Block and surrounding area.