Experimental Investigation on Propagation Behavior of Hydraulic Fractures in Coal Seam during Refracturing

Table 3

Experimental parameters and results of refracturing in coal.

Specimen number	(MPa)	Breakdown pressure; (MPa)		Fracture geometry
		Initial fracturing	Refracturing
1	2	9.28	4.54	Initial HF connected with cleats, no new HFs were formed
2	2	4.14	2.97	Initial HF was initiated from cleats, no new HFs were formed
3	2	5.23	3.15	An initial HF connected with cleats and BPs, no new HFs were formed
4	4	8.86	11.30	A new HF was perpendicular to the initial HF
5	4	23.03	16.40	New branches propagated along cleats
6	4	8.47	5.36	New HFs connected with cleats
7	6	15.02	13.65	New HFs were perpendicular to the initial HF
8	6	12.68	7.34	A simple initial HF connected with cleats, no new HFs were formed
9	8	4.46	1.82	A HF network consisting of initial HFs and cleats, no new HFs were formed
10	8	13.58	8.74	A initial HF connected with cleats and two BPs, no new HFs were formed