| Acidification is the treatment of oil and gas layers with acid or latent acid to restore or increase the permeability of the reservoir.And it can increase oil and gas well production.Matrix acidification has been widely used as one of the important stimulation methods in the development of carbonate reservoirs.The hilly mountainous area is a severely waterdeficient area in northern Hubei Province,China.In this paper,the acidification technology is applied to the production technology of water wells,and the interaction mechanism between acid and rock based on water well stimulation is studied.The formation of the pores by acidification of the bedrock increases the permeability of the aquifer,thereby solving the problem of water shortage in the area.And thus,establish an acidification system suitable for acidification of carbonate rock bed water wells.In the actual acid system,the reaction rate is too fast,the corrosion is strong,and it is difficult to form an effective acid wormhole.However,the chelated environmental acid system represented by a chelating agent can forming effective pores and low corrosiveness to metals,but due to its slow chelation with limestone,more time is required to form the wormhole in actual engineering.Here,based on the research and analysis of the physical and chemical properties of the Baota Formation limestone in the Zigui area of Yichang City,Hubei Province,we study the interaction mechanism between conventional acid and environmentally friendly acid for low permeability limestone.And the acid type and concentration of the superior performance are selected.The acidification working fluid system suitable for the bedrock carbonate rock well is constructed,it can provide theoretical basis and technical support for the engineering practice.The paper is divided into six chapters.The main contents of each chapter are as follows:The first chapter briefly introduces the background and research significance of the paper.It introduces the current technical level of acidification and stimulation of carbonate matrix in the world,and explains the disadvantages of acidification of conventional acid solution,and puts forward the key problems and technical routes to be solved.The second chapter analyzes the basic characteristics of the Baota Formation limestone in the Zigui area of Yichang City,Hubei Province.The types and applications of conventional acid and environmental acid are introduced,and the chelating ability of the chelating agent used in the experiment is evaluated.The third chapter studies the effect of conventional acid on the physical and chemical properties of the Zigui Baota limestone.It was found that hydrochloric acid,formic acid and phosphoric acid in the conventional acid have higher corrosion rate to the Zigui Baota limestone.But at the same time,they have strong corrosion ability to the metal test piece,and in the core flow experiment,hydrochloric acid easily forms surface corrosion of the rock sample.It is difficult to deepen acidification.And acetic acid has a good retarding effect on the limestone and exhibits a lower corrosion rate for metal coupons.In the core flow experiment,the limestone is acidified to form a relatively small diameter wormhole,and it is not easy to form face corrosion.Through the evaluation of the conventional acid system,the formula of the conventional acid system suitable for acidification of the matrix water well of the lowpermeability carbonate reservoir was determined by experiment,it is: 8% hydrochloric acid + 6% acetic acid + 0.2% LV-CMC +0.1% water soluble imidazoline.Its permeability increased by 100-300 times before and after acidification of the Zigui Baota limestone.And corrosion rate of standard metal corrosion test piece P110 for 24 h is 0 g/(m2×h),excellent corrosion inhibition effect.The internal pores of the acidified rock samples were observed by CT scanning method.It was found that the acid system significantly increased the porosity of the limestone rock samples,which was basically consistent with the previous experimental results.The fourth chapter studies the effect of environmentally friendly acid on the physical and chemical properties of the Zigui Baota limestone.The chelating acids GLDA and MGDA have a good dissolution rate for the Zigui Baota limestone,and MSA(methanesulfonic acid)as a degradable organic strong acid has a high dissolution effect on the Zigui Baota limestone.Experimental study on environmentally friendly acid in core flow experiments found that GLDA is easier to form wormhole on rock samples than MGDA.And experimental study on the influence of GLDA concentration,p H and injection rate on the permeability of the Zigui Baota limestone,it was found that the 3% GLDA(p H=4,HAC)solution had a significant effect on increasing the permeability of the Zigui Baota limestone at a flow rate of 1 m L/min.Through the optimal evaluation of the environmentally friendly acid liquid system,the experiment determined the matrix acidification environmental acid system suitable for the low permeability carbonate reservoirs,it is: 7% MSA + 3% GLDA(p H=4,HAC).After the system acidified the Zigui Baota limestone,the permeability of the rock sample increased by about 400 times,and no large surface area corrosion was found on the surface of the rock sample after acidification.And even if no corrosion inhibitor was added,the metal test Sheet P110 still has a good corrosion inhibition effect.The internal pores of the acidified rock samples were observed by CT scanning method.It was found that the acid system significantly increased the porosity of the limestone rock samples,which was basically consistent with the previous experimental results.The fifth chapter summarizes the full text and puts forward the main innovations and further research ideas.There are two main innovations in this article:(1)Based on laboratory experiments,the dissolution mechanism of low-corrosion,biodegradable chelating acid GLDA(glutamic acid N,N-diacetic acid)and organic acid MSA(methanesulfonic acid)on the Zigui Baota limestone was studied.And the corrosion mechanism of the metal,and the research determines the optimum flow rate and concentration of the chelating acid in the acidification process of the Zigui Baota limestone.(2)Through the laboratory experiment,the interaction mechanism between conventional and environmentally friendly acid with the low permeability limestone is studied.And two sets of acid liquid system are constructed accordingly,which is suitable for increasing production of hilly mountainous areas in northern Hubei or other areas of representative low permeability carbonate resources. |
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