Optimization of multi-stage cluster spacing in deep coal seam horizontal wells considering cleat

Abstract

In order to study the horizontal well multi-segment multi-cluster fracture extension in the deep coal reservoir where the cleat fissures are developed, a multi-segment multi-cluster fracture extension model is created based on the extended finite element and taking into account the inter-seam interference and the induced stress field. With the secondary development of pre-processing in Python language, a large number of approximately orthogonal cleat fissures were added into the model. The effects of cluster spacing, fracturing sequence and segment spacing on multi-fracture extension were analyzed, and the advantages and disadvantages of fracturing effect were verified by querying the number of fracture-communicating cutting groups. The simulation results show that when the cluster spacing is 20 m and the segment spacing is 40-45 m, the number of fracture communication cutting groups is relatively high, and the fracture length is optimal due to the small influence of inter-seam interference and induced stress field; at the aspect of the influence of different fracturing sequences on the extension of multi-fractures, the fracturing effects are ranked from excellent to poor: sequential fracturing > alternating fracturing > synchronous fracturing. The results of modeling and field application are in good agreement, with 96.5% for the second fracturing section and 93.4% for the third fracturing section.

Keywords

• deep coal-rock reservoir
• segmented cluster fracturing
• cleat fissure
• induced stress
• extended finite element