Study On The Acidizing Technology For Chengbei Oil Reservoir

Chengbei oilfield reservoir Guantao formation have many layers.Heterogeneity between layers and layers is serious.Because of the inject well water quality is poor,the injected water and formation water is not compatibility,high mechanical impuritiesand long-term water injection.In order to solve the current situation of high pressure water injection,it is necessary to carry out effective research on reservoir reconstruction technology in order to improve the development effect.This paper aims at the above problems.Based on the analysis of reservoir charac-teristics and pollution reasons of the Guantao formation,we optimize the acidizing fluid system of Chengbei oilfield.The corresponding design method of layered acidizeng scheme is formed.The structure of layered acidification column is confirmed.The optimized design and application effect statistics of layered acidizing of Chengbei A well are completed.We provide technical support for reducing water injection pressureand improving development effect.The results show that:based on the formation characteristics of Guantao Chengbei oilfield,a large amount of suspended matter enters the formation to form ablockageduing the course of development.There are big differences between the marine environment of sea water and formation water salinity,Ca²⁺ion content.The CO₂ in the water separates out due to the pressure unloading,and it is easy to form carbonate brine toblock the formation.Because of the thermodynamic instability of the injectedwater,chemical instability and a large number of scaling salts and other factors,it cause the formation of a blockage near the bottom of the well,and it affects water floodingeffect.The reservoir needs to be acidified.The mud acid system is suitable for the block.Acidizing fluid formulation:ahead fluid:15%HCl+5%NH₄Cl+2%A/Inhibiter+1%Festabilizer+2%B/clayinhibitor+2%B/acidmutual solvent;mainpartfluid:15%HCl+2%HF+5%NH₄Cl+2%A//inhibiter+1%E/Festabilizer+2%B/cl ayinhibitor+2%B/acidmutual solvent;post fluid:15%HCl+5%NH₄Cl+2%A/inhibiter+1%E/Fe stabilizer+2%B/clay inhibitor+2%Bacid mutual solvent;displacement fluid:5%NH₄Cl.The results of the evaluation of the compatibility and blocking test show that the system has stable performance and good compatibility.The design of marine stratified acidizing in Chengbei oilfield include well and layer selection,seperate layer acid treatment selection,confirm maximum injection pressure and injection output volume,confirm the amount of acid solution.Combined with the construction requirements,we choose the seperate layer acid treatment technology by pakers.We achieve the accurate positioning by the corresponding downhole tools as the combination of the water distribution device,the backwash valve and the oil pipe anchor.The optimum design of the layered acidizing in Chengbei A well is taken as an example,After the acid treatment,the water injection pressure from 11.7MPa to 3.4MPa.The increment of water injection rate is from 215m³/d to 254m³/d.Application of 68 horizons of technology of stratified acidizing in injection wells in Chengbei oilfield.The construction of the success rate is 100%.The daily water injection pressure was reduced after acidification,daily water injection rate significantly increased.Oil yield Cumulative increases 2680t,and injection water increase 252000t.It is a good reference and guidance for other production/injection wells reservoirs which have high porosity and permeability to increase yield and injection in the Bohai Bay.