Pattern Recognition of the Vertical Hydraulic Fracture Shapes in Coalbed Methane Reservoirs Based on Hierarchical Bi-LSTM Network

Table 1

The criterion of the fracture propagation manner according to the lgP-lgt curves.

Propagation manner	Slope of lgP-lgt curve (e)	Corresponding interpretation
I	e < −0.2	(a) The fracture passes the formation of low stress and its height is out of control
		(b) The natural microfractures are encountered and connected.The fracture propagation satisfies the KGD model
II	−0.2 ≤ e < −0.125
III	−0.125 ≤ e < 0.167	(a) The facture height increases slightly
		(b) The natural fractures are open, and the fluid loss increases
IV	0.167 ≤ e < 0.25	The fracture propagation satisfies the PKN model
V	0.25 ≤ e < 1	The pad fluid loss is too much and the proppant ratio in the fracture head is high, the fracture propagation is limited, end sand out happens
VI	e > 1	(a) The fracture width is too small, the proppant agent is plugged in the fracture, the consequent fluid injection can only expand the fracture width and height
		(b) The pressure sustainably high, the number of fractures might increase
		(c) The facture encounters the sealed beds of high stress