Weak Gel Deep Profile System Laboratory Research Of Chaheji Oilfield

Chaheji oil field reservoirs have high temperature (67℃~95℃), large formationwater salinity (13380mg/L~47168mg/L), and strong heterogeneity, all the main blockhave entered the high water late stage of development, but there are still55%~60%ofthe remaining oil stored in the ground, regular oil displacement system formula isdifficult to continue to improve the recovery ratio of the petroleum. According to thedifferent main fault blocks oil reservoir geological characteristics of Chaheji oilfield, ithas a very important practical production significance to carry out weak gel deepprofile EOR research. In this paper, I take the main fault blocks of cha4, cha12, cha15and cha39for example, carry out a laboratory study of weak gel deep profile EORmethods.Laboratory experiment results show that under no shear conditions the preferredoptimum formulation of deep profile of Chaheji oilfield weak gel: the polyacrylamideHPAM (produced by Daqing Additives Factory) concentration is1200mg/L, relativemolecular mass is1800×104, the crosslinkers concentration of hexamethylenetetramine (methenamine) is600mg/L, the crosslinkers concentration of resorcinol of is500mg/L, the modifier concentration of oxalic acid is600mg/L, the heat stabilizerconcentration of MN is200mg/L. The system generally has a longer stable gel time（about28hours）, a stable gel strength between7000mPa.s and10000mPa.s.Under high shear conditions, the strength of the weak gel will be greatly reducedand the stability will decline. After a high-speed shear, the relative molecular masswill decrease, and the weak gel system effective concentration and proportion of eachcomponent will change. At this time, as the concentration loss in the high shear, thebest formulation is not the best, therefore, under high shear conditions to change thecomponent concentrations of the weak gel system to make an optimization. Underhigh shear conditions, the preferred optimum formulation of weak gel deep profile: thepolyacrylamide HPAM concentration is1300mg/L, relative molecular mass is1800×104, the crosslinkers concentration of hexamethylene tetramine (methenamine)is650mg/L, the crosslinkers concentration of resorcinol of is550mg/L, the modifierconcentration of oxalic acid is650mg/L, the heat stabilizer concentration of MN is 240mg/L. Under high shear conditions, the system generally has a longer stable geltime（about30hours）, a stable gel strength between3500mPa.s and6000mPa.s, goodstability, long aging dehydration time. Under high shear conditions, the weak gel deepprofile system has a good performance in the reservoir conditions of cha4, cha12,cha15and cha39block, the weak gel system has a best stability in the Cha4reservoirconditions, a relatively weak stability in the Cha12reservoir conditions by contrast, butits gelling effect can reach the weak gel deep profile purposes under different faultblock reservoir conditions,and its aging dehydration time is more than120d. Overall,the performance and stability of the weak gel deep profile system is very good.The results of coreflood experiments show that the best slug of Chaheji oilfield is0.35PV, it is suitable for "low viscosity, large slug" of weak gel deep profile system. Forweak gel deep profile EOR, the long-term stability problems of the weak gel systemafter injection in the reservoir must be considered. In general, under high shearconditions, the optimized weak gel system has a good gelling performance and goodstability.Through the optimization of experimental analysis of the best prescription systemunder different conditions of fault block oil reservoir, we can know that under highshear conditions, the best weak gel optimized formulation system under the reservoirconditions of Cha4block is that: the HPAM concentration is1300mg/L, relativemolecular mass is1800×104, the concentration of crosslinker methenamine is600mg/L,the concentration of crosslinker resorcinol is580mg/L, the concentration of modifieroxalic acid is600mg/L, the concentration of stabilizer MN is180mg/L; the best weakgel optimized formulation system under the reservoir conditions of Cha12block is that:the HPAM concentration is1300mg/L, relative molecular mass is1800×104, theconcentration of crosslinker methenamine is650mg/L, the concentration of crosslinkerresorcinol is550mg/L, the concentration of modifier oxalic acid is650mg/L, theconcentration of stabilizer MN is240mg/L; the best weak gel optimized formulationsystem under the reservoir conditions of Cha15block is that: the HPAM concentrationis1300mg/L, relative molecular mass is1800×104, the concentration of crosslinkermethenamine is680mg/L, the concentration of crosslinker resorcinol is500mg/L, theconcentration of modifier oxalic acid is650mg/L, the concentration of stabilizer MN is200mg/L; the best weak gel optimized formulation system under the reservoirconditions of Cha39block is that: the HPAM concentration is1300mg/L, relativemolecular mass is1800×104, the concentration of crosslinker methenamine is650mg/L,the concentration of crosslinker resorcinol is500mg/L, the concentration of modifier oxalic acid is600mg/L, the concentration of stabilizer MN is180mg/L. Under highshear conditions, each optimization system in each reservoir conditions, it has a stablegel strength between3500mPa.s and6000mPa.s, the beginning dehydrated time ismore than120d, high reach about170d, completely dehydrated time is more than160d, high reach about210d. The weak gel deep profile system has a preferably gelstrength and a strong stability. From the gelling performance of a long time (160d)point of view, the further optimized weak gel system of each block can satisfy therequirements of weak gel deep profile in its block reservoir conditions.Numerical simulation of an ideal model shows that with increasing aging time, theweak gel viscosity retention rate decreased in the formation，and compared with thesituation under the unaged, there are different ranges of decline in the EOR than thewaterflood, the increased amount of oil, the T oil increment of polymers, and thecomposite indicator. Overall, the predicted effect of numerical simulation is relativelygood, the best slug of the maximum value of the composite indicator is0.3PV, weakgel deep profile can enhance oil recovery of4.96%OOIP rather than the waterflood.Theoretically, weak gel deep profile can play a better oil displacement effect.