Study And Aplication On The Stimulation Fluid In Hancheng Block Of The Eastern Ordos CBM Field

Hancheng area is located in the southeast margin of Ordos basin,it is the first commercial CBM demonstration area in the Eastern Ordos CBM Field,with low porosity?low pressure?low permeability reservoir characteristics.The single well production is not high.To improve the single well effect,avoiding the damage of fracturing fluid,coal powder,etc.during fracturing,and making sure the water output of each coal seam after fracturing,this study is conducted.This paper started with the Hancheng coal reservoir characteristics,studied the mechanism of coal damage and the damage evaluation,proposed a new method of evaluating the liquid desorption damage,established a new technology of estimating the drainage in each seam for the multi-layer fracturing well which is exploiled together,and devolopped a new active water fracturing fluid system.The main research results as follows:1.The Hancheng coal reservoir has some characteristics such as well development of micropore,large specific surface,low porosity,low permeability and so on.The pore's type,sensitive minerals,variation of stress are closely associated with potential damages.The major cause of permeability damage is the retention of fracturing fluid in the pores and the particle surface.Experiments show that the Hancheng coal reservoir has some other characteristics,including weak velocity sensitive,none water sensitivity,mid-alkali sensitivity and stress sensitivity.2.The high-pressure injection is deviced,and an evaluation method of coal reservoir damage of foreign liquid is set up.It is the first time that we can evaluate the coal reservoir damage of foreign liquid through the adsorption-desorption isotherm curve.Furthermore we improved the evaluation experiment of operating fluid damage to reservoir,which can provide important experimental basis for optimize formulas and the development of fracturing fluid?3.After analyzing harm of coal powder and its cause,studying on wettability between the surfactant and coal powder,MF-1 is developed.MF-1 is a coal powder suspending agent whose main ingredient is a non-ionic surfactant.MF-1 has well suspended ability,also it can reduce surface tension of liquid and conduce to liquid discharge,and has low damaga on reservoir.4.Based on the mechanism of coal reservoir damage,combined with the regional coal reservoir characteristics,a new active water fracturing fluid system(1%KC1+0.5%MF-1)is created.The new active water fracturing fluid has merits such as well suspended ability,prevention of swell and low damage.It can satisfy the requirement of CBM fracturing of low cost,simple operation,so it is recommended for fracturing operation in Hancheng.5.Screened out two types tracers(ammonium rhodanate and sodium nitrate),and put forward two new methods of improve accuracy of NO3-.For the first time,the drainage tacer technique for CBM wells is proposed.Adding deferent chemical tracer in each layered fracturing,by detecting the flowback fluid tracer's concentration,we can calculate and analyze the liquid production from different layers.Compared with other testing technology,this method is simple,economically feasible,none-effect on production and none damage.6.Applying the new active water fracturing fluid has finished fracturing in 12 Wells on 20 layers.Each well keeps pressure smooth during fracturing.On preliminary stage,the drainage contains a large number of coal powers.After fracturing,the effect is obvious and the well can be burning.Tracer liquid injection experiments are completed in 2 wells,and the estimation of stratified fluid volume is in accordance with the production situation.Now the patent for invention has been applied.