The Research Of Polymer Prprofile Control System And Pilot Performance In A Low Permeability Oilfield In Yanchang

An oil pool of Yanchang oilfield,being called YC Oilfield,belongs to a low porosity,low permeability reservoir,with the characteristic of low reservoir pressure,low reservoir permeability,low well production,early water breakthrough and water cut rising.The gel solution used to modify profile is determined or screened out based on the profile modification theory and technology to improve the sweep efficiency or enhance oil recovery at the reservoir conditions and geological characteristics.The polymer solution is difficultly forced or injected into the low permeability reservoir,penetrating in small pore throat with a large gyration radius.Unfortunately,the non-ideal effect of enhancing oil productivity can also be caused by the PAM or HPAM solution forced into the pore throat with a small gyration radius,because of the poor gel strength of polymer solution.However,HPAM cannot be used to YC Oilfield for its poor long-term stability,poor salinity and shearing tolerances.In conclusion,designing a new hydrophobic associating polymer?CK-TP03?with medium or low relative molecular mass,three-dimensional space network structure,comb-like shape and strong dissolving power,is extremely urgent.Because the hydrophobic groups are linked at polymer chains,the main profile modification agent CK-TP03 could gel enough to reach at a required gel strength by using little cross-linker agent.Thus,the cross-linker concentration and cross-points are reduced through this technology.The shortage caused by gelling overly such as dehydrating sharply and rapidly can be avoided.Thus,the research implemented about CK-TP03 can not only be of theoretical significance,but also be of realistic one.Most cross-linking systems and various influential factors are investigated in order to find out the ideal system and master gel rules.Pilot oilfield tests have been carried out based on the effect of indoor tests and oil displacement experiments which are implemented at the reservoir conditions.The synthetic results and the design of molecular structure indicate that the optimal raw materials ratio and reaction conditions are as follows:six hours under the function of complex initiator system;polymerization temperature at 35?;the concentration of polymer monomer AM is 25 wt%;the molar concentration of Acrylic AA is 30 mol%;the hydrophobic monomer molar concentration is 0.8 mol%;the carbon numbers of this hydrophobic monomer is 18;the component of this complex initiation system are as follows:the concentration of K₂S₂O₈ is 20 mg/L;NaHSO₃ is20 mg/L;AIBN is 36 mg/L;urea is 240 mg/L;the ideal dissolving concentration is2000 mg/L to 4000 mg/L with the particle size of 40 to 50 mesh number.The performance results about studying gel profile modification system show that the optimal formula for polymer gel is as follows:the concentration of main reagent CK-TP03 is 3000 mg/L;oxalic acid is 800 mg/L;urotropine is 750 mg/L;resorcinol is400 mg/L.Compared with the gel system HPAM under the condition of using the same cross linking agent,gel system CK-TP03 possesses a longer-term stability and a stronger shear tolerance.200 days after used,the gel strength still can reach 52000mPa?s with the recovery rate keeping at 89.4%after being sheared about 120 seconds and the viscosity retention rate keeping at 78.8%.The results of core flow tests show that:?1?Non-gel system of CK-TP03possesses excellent fluidity,good injection but poor sealing characteristics;?2?Residual resistance factor decreases with the increase of the injection rate.?3?The polymer solution owning selective plugging function,it is preferentially injected and effectively plugged the high permeability reservoir,with the consequent to protect the lower permeability reservoir.?4?Profile modification system CK-TP03 can be driven.It deforms in the driving process,causing a fluctuant displacement pressure.?5?Profile modification system makes a high stemming ratio for cores,and the stemming ratio,enlarging with the increase of injection volume,can reach more than 91.3%at the injection of 0.45 PV.?6?Profile modification system CK-TP03 possesses high erosion resistance.The stemming ratio can keep at more than 82%after being eroded by 70 PV water.?7?The breakthrough pressure gradient will enlarge with the increase of flow rate after being injected CK-TP03.?8?Excellent profile modification function and higher recovery ratio,increasing by 20.18%than water drive recovery efficiency,are confirmed by the results of core flooding test.Prominent problems from the water-flooding of 121 and 127-8 well group make the wells good areas of field test.The results from the pilot field test show that profile modification agent CK-TP03 of YC Oilfield is excellent in oil increment.The accumulated oil increment of the well groups is 289 t and 229 t respectively;the composite water cut of them decreases by 20%and 18%,from 82%and 79%to62%and 61%,respectively;daily oil production increases by 1.59 t/d and 1.26 t/d,from 0.63 t/d and 0.51 t/d to 2.22 t/d and 1.77 t/d,respectively.This system,suiting for reservoir geological conditions,features good shear tolerance.It promises great increase in productivity and economic gains.