| There are so many differences between characteristics of the coal seam and conventional reservoir sandstone, carbonate rock, it is self-generated adsorbed gas from reservoir, fragile, low mechanical strength, cleat development, complex structure, and the homogeneity is so poor, the pore structure belongs to matrix micro pores and cracks, porosity and permeability is very low, It changes in production significantly,it absorps atmospheric pressure or low-pressure,these characteristics determine that CBM is extremely difficult to exploit.Acidification is a most importmant measure on oil and gas wells production, and the experiment is very importmant technical support, it based on basic theory,choosing the best acid system and acidification process.Compared to the field what have acidification,this method is more comprehensive、 timesaving and low power. Therefore,based on the specific properties,we choosed coal and fluid to simulate the reservoir conditions in acidification experiment, and then we could find out the reaction mechanism between coal and rock conveniently and accurately,it is guarantee for field application in future.In this paper, the coalfield we study is qinshui coal-bed meathne field, the main part is located in the south of Shanxi Province, the structure is in the slope zone which is in the south of qinshui basin, porosity in qinshui basin coal reservoir porosity is lower than5%generally,and the permeability is lower than1.0×10-3μm2. Coal pore pressure coefficient is0.91～1.02, is lower than hydrostatic pressure. We combined the physical and chemical characteristic which about Sihe、Fenghuang、Changzhen mine in Zhengzhuang and Fanzhuang areas, learning from the acid stimulation treatment which in conventional gas wells,using the indoor static experiments and best acid system and acid additive to put forward the viable acidizing program.We could recognize the chlorite、smectite and illite is much more in clay minerals of Zhengzhuang and Fanzhuang in Qinshui Basin through analyzing the three mines’characteristics.When the extraneous fluid comes into coal seam,it lead to hydrous disintegration of formation water,and then make the permeability of CBM decline.So we direct at the reservoir property,selecting the best clay stabilizer is KCL and HES.As the Coal seam water contained Na+, K+,Mg2+, Ca2+and so on, the acid with these ions cause harmful sediment, so as to bring the secondary damage in formation. Thus prevented the precipitation of iron ions effectively is the key which effecting the acidification.In this paper, we use iron ion complexing agent,comparing the stability of several iron chelator,to choose the best ferrous stability.The residual acid will increase the water saturation, reduce gas penetration after coal acidificatiom.It makes the acid effecting lower.It’s very difficult in this condition that the power and permeability in formation is not very good.If acid can not drainage from formation rapidly,maybe it will cause more serious clogging—capillary absorption roal,it makes capillary clog,and then lead to Water locking seriously, damaging the formation,so we must add the cleanup additive after acidification. Through the experiment,we choose the best cleanup additive is YBZP-3、OP-10.The effectiveness of acid formulations also depends on the effect of formation acidification finally.We have the dynamic evaluation test in lab,according to the acid that we choose on static dissolution rate,having acidification effects test with Zhengzhuang core,tested the variation of porosity and permeability.In the end,we find that coal pore structure have been significantly improved after acidification,1hour is the best period for acidification processing,the permeability of core will be the best one. We use acid system:main acid is mud acid:15%HCl+(2.0%to3.0%) HF+1.5%to2.0%ferrous stability+0.5%～1.0%clay stabilizer+0.4%cleanup additive, pre-washed with hydrochloric acid:15%HCL. |
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