Research Of Reservoir Blocking Agents Used For Carbon Dioxide Flooding

Most reservoirs in China are continental sedimentation,with complex cyclothem.At present,the water cut of those major oilfields is as high as 85%,and some is higher than 92%.Heterogeneity of those reservoirs is obvious,and high capacity channel is widespread,with scattered remaining oil.Therefore,the common water flooding,chemical flooding and microbian oil recovery technique could not meet the demand of those maturing fields,and the task to enhance oil recovery is quite difficult.Nowadays,gas injection technology has become an effective way for EOR,and carbon dioxide flooding is one of the major useful methods.However,gas channeling is the chief problem of carbon dioxide flooding.Most reservoirs could not be swept because of the premature breakthrough,which affects the exploitation results.Therefore,it is quite important to block the high capacity channel to avoid the gas channeling during carbon dioxide flooding.Domestic plugging technology for carbon dioxide flooding is only developed recently,and is seldom used in-situ extensively.In the Gao 89-1 block low permeability reservoir of Shengli oilfield,because of the nature and artificial fracture and the heterogeneous matrix,the carbon dioxide broke through while injection.In order to gain good results,the key point of carbon dioxide flooding is to develop effective blocking agents.In this paper,two types of polymer gel system are developed for carbon dioxide flooding,which are HPAM/Cr³⁺ gel system and NMH-1 gel system,and the performances and influence factors are researched.The two systems provide effective technical guarantee for carbon dioxide flooding in the Gao 89-1 block.The main researches of the HPAM/Cr³⁺ gel system include: change the compositions of the system,measure the gel performance,select the best formula using uniform design method.The gelation time of this formula is long,with high intensity and good stability.The core displacement experiments show that this system is quite useful to block the carbon dioxide channeling.This gel entered into the high permeability layers or high capacity channels first and seldom flew in the low permeability layers,demonstrating the good selectivity.But if met high temperature higher than 100? or strong acid,the gel is easily to dehydrate.The main researches of the NMH-1 gel system include: using the high temperature of the reservoir,the polymer could polymerize and cross link automatically.The formula of the gel system is selected through the research of AM,various additives,temperature and the gelation behavior under high temperature and supercritical carbon dioxide.Quiescent performances are evaluated through the experiments of long-term stability,the influence of PH value and salinity.The core experiments results show that,the gelation effect of the system is good,with high plugging strength.The carbon dioxide flooding plug experiments demonstrate the excellent plugging effect of the gel system.In view of the reservoir characters of the Gao 89-1 block of Shengli oilfield,the NMH-1 gel system is selected as the plugging agent,and the plugging project is worked-out.