Static Fracturing Increasing Low Permeability Coal Seam Basic Experiment Research

The underground coal seam is rich in coalbed methane in our country.Coalbed methane resources is one kind of good clean energy in the field of energy,it has high calorific value and no harmful gas after combustion.Coalbed methane main composition is methane,coal bed methane abnormal emission can cause gas accidents.If methane emissions into the air directly,it will cause the greenhouse effect.So reasonable utilization of coalbed methane resource is not only benefit to make full use of energy,but also protect the environment,at the same time,it can avoid the gas accident to ensure coal mine safety production.Coal seam in China generally have the characteristics of heterogeneity,low permeability and high gas content,these characteristics make it difficult in gas extraction directly,therefore improve the low gas permeability of coal seam permeability has become the bottleneck of restricting the mine gas extraction.Static blasting technology is also called silent blasting,is the technology which use static blasting agent mixed with water producing expansion pressure acting on the wall of shothole.Static blasting technology has many characteristics,such as no flying rock,no blasting sound,no shock wave and no blasting vibration.It is also easy to operate and security.So it has good prospect in the application of increasing low permeability coal seam.This paper presents that applying static fracturing technology to achieve the purpose of increasing the permeability of low permeability coal seam,developing basic experiment research in increasing low permeability coal seam by static fracturing technology.This paper mainly analyzes the principle of static fracturing and the process of fracturing static stress in each stage;homemade static fracturing agent,using the orthogonal test to acquire the preliminary optimum ratio after determining basic components;designing experiments to study the effect law between static fracturing agent fracturing effect and factors which include borehole shape,environment temperature,lime particle size and the pH of the water.In this paper,the main conclusions are as follows:(1)The principle of Static fracture agent cracking is through expansion source CaO hydrate with water to generate Ca(OH)2,during hydration process fracture agent volume expand producing expansion pressure acting on drill wall.The CaO hydration process can not produce expansion pressure in free state without in constraint condition.Cracking process can divide into two stage,one is elastic phase,the other is inelasticphase.With circular hole as an example,the elastic stage radial stress constant as the compressive stress,hoop stress is tensile stress,stress is the same around the borehole.When the pressure increases to a certain value,the fracturing process into the inelastic phase,the damaged area appear,create many micro cracks.The largest micro cracks cause cracking and crack propagation.(2)The major component of static fracture agent should include expansion source,water reducing agent,retarder,cementing agent.We choice the specific components include Quick Lime,Naphthalene Series Water Reducing Agent,Sodium Gluconate,Portland Cement,through orthogonal test acquire the optimum ratio: Quick Lime: Naphthalene Water Reducing Agent: Sodium Gluconate: Portland Cement = 90:3:5:7.Through XRD test found that during static fracture agent generate expansion pressure to expansion pressure completely release,the growth of expansion pressure is variational,early speedup higher than later.(3)Drilling shape will affect static fracture agent crack effect.When drilling is a round hole,the hole will form stress concentration area near the edge sharp point,with the increase of expansion pressure,craze will first appeared in the stress concentration areas of briquette coal,cracks extend in the direction of the sharp point.(4)Environment temperature,quick lime particle size,PH of water will influence on the static fracture agent crack effect.Environmentaltemperature has a significant impact on briquette coal cracking effect,between 20 to 50?,with the increase of ambient temperature cracking time became shorter.The too large lime particle size can not completely release the fracturing property of static fracture agent,the static fracture agent with particle size of 6 to 18 quicklime show the best fracturing performance.The static fracture agent with alkaline water has better fracturing performance than acidic water,but when basicity reaches a certain value,with the ascension of alkaline fracturing performance began to decline,when the water PH is 8 fracturing effect is the best.