Research On Optimization And Mechanism Of Acidification System For Tight Reservoir

The Chang 8 reservoir in Honghe Oilfield is rich in reserves,but the reservoir is dense,the pore throat is small,the crack is developed,and there are problems such as high water injection pressure,large matrix displacement pressure gradient and low crack re-tension pressure.It is difficult to achieve economic and effective development.Long 8 reservoir pores have more fillers,which is the key factor leading to low permeability.Therefore,the method of dissolving minerals in the pore throat is proposed to increase the pore throat and reduce the injection pressure and increase the yield.In this paper,the engineering geological characteristics of the Chang 8 reservoir are firstly analyzed,including reservoir mineral composition,pore throat structure,reservoir sensitivity,etc.,which clarify the main factors affecting the acidification to achieve pore and throat enlargement;combined with numerical simulation analysis,The treatment method of the reservoir is determined.The dissolution main agent was screened by the dissolution test and the dissolution filtrate analysis,and various additives were tested and evaluated.The main agent is optimized according to the dissolution rate of the acid rock reaction and the cation content in the solution.The effect of depressurization and anti-seepage,the change of ions in the solution with time,and whether the residual acid produced after the residual acid solution penetrated into the reservoir were evaluated.Finally,changes in pore throat level and connectivity before and after acidification of the reservoir were demonstrated by core sheets,CT scans and mercury intrusion experiments.The variation of the rock sample composition,the core section and the microstructure of the inner surface of the pore were analyzed by whole rock composition analysis,SEM scanning and EDS spectrometer.The reason for the low reservoir permeability is that there are more fillers in the pores,and the carbonate content is higher;there are easily precipitated cations in the formation water,and the acid sensitive minerals in the reservoir are more;the clay film on the inner surface of the pores reduces the pore radius and so on.The best acidification formula suitable for Chang 8reservoir is selected from 5% hydrochloric acid,1.6% citric acid,0.4% acetic acid,0.2%corrosion inhibitor and 0.05% active agent.The selected system is injected into the formation in one step,and the process is simple.The precipitation can be effectively controlled,and the corrosion rate of the steel is within the first standard.The indoor core flow experiment shows that the permeability of the reservoir rock sample can be increased by up to 400%,and there is no secondary damage to the formation.The residual acid solution can continue to realize deep reaming and throat enhancement.Microscopic analysis of the rock samples before and after acidification showed that the target corrosion was effectively dissolved,and the pore throat was expanded to different extents.The effect of pore acidification of less than 0.13 ?m in the reservoir with higher permeability was not obvious.The clay mineral film on the inner surface of the pores has a reduced volume after dissolution,the inner surface of the pores becomes smooth,and the tortuosity of the pore throat is low.