Based on the technological features of small nitrogenous fertilizer production system and the analysis of fire & explosion risk factors in the production of nitrogenous fertilizer,Dow method is used to calculate the inherent risk index and the actual risk index of six assessment units of coal gas producer,gas tank,desulfurization,transformation,cuprammonium washing and synthesis.

At first,on the basis of the geological features,24 types of oil assessment units and 16 types of natural gas assessment units were classified,such as the high-permeability unit in the Mesozoic depression,the high-permeability unit of complicated fault blocks in the rift basin,cratonic basin palaeo-high,foreland basin thrust fault.

The assessment units should be divided into different types, each type had its own solution.

In the technique of safety evaluation, marking off evaluation unit accurately is a key point.

On the basis of the grey system theory with the evaluation of coal resources,the paper discusses the grey characteristics of evaluation unit of coal resources,analyses the basic principles of evaluation of coal resources with grey cluster,and gives the calculating method in the evaluation of coal resources.

It is introduced the application of pattern recognition method,the leading method is neuralnetworks pattern recognition,in geochemistry inclued oil and gas evaluation,geochemical explortion and sedimentary microfaci.

Application of Bayesian statistical pattern recognition in mud log oil-gas evaluation;