| The pace of Tahe carbonate fractures is variety and the fractures is the main flow channel of fluid,which cause the injection water and formation water flow quickly to the production wells along the fractures.Those will influence the overall development and economic benefit.So,it is urgent that water shutoff measures should be taken to control the fracture water to increase the oil recovery and improve the overall development.The conventional plugging agents don't have high strength,excellent saline and thermal stability and oil and water selectivity.Therefore,the following study was carried out to construct a water and oil selective plugging agent with saline and thermal resistance for the Tahe carbonate fractures in this paper.(1)An unstable crosslinking agent was introduced into the anti-temperature and salt-resistant monomer(RHSM),and the non-stable crosslinked particles(NCP)were synthesized by monomer polymerization.The optimal formula of the NCP is:25%RHSM+0.15%Unstable crosslinking agent P-1+0.1%Initiator.The NCP can decompose with the secondary crosslinking agent P-2 to form a particle type secondary crosslinking agent under the condition of water phase.The optimal formulation of the plugging agent is:3?4%NCP+0.4?0.5%P-2+1.5%delayed crosslinking agent,which gelation time is 10h and the strength can reach code J at 115? and 2 × 104 mg/L.(2)In order to further improve the salt tolerance of NCP particles,the non-stable crosslinked intercalated particles(MNCP)was synthesized with the sodium-based montmorillonite and salt-resistant monomer N-1 on the basis of NCP.The optimal formula of the NCP is:25%RHSM+7.68%5#Sodium-based Montmorillonite+1.875%N-1+0.76%Intercalator+0.75%Suspension+0.15%P-1.The thermal decomposition of MNCP can be crosslinked with the secondary crosslinking agent FQ-2 in the aqueous phase to form an intercalated particle type secondary crosslinking plugging agent with delayed crosslinking performance.The best formulation of the blocking agent is:4?5%MNCP concentration+0.6?1%FQ-2+1.5%delayed crosslinking agent,which gelation time is 24h and the strength can reach code I at 1?5? and 10 × 1 04 mg/L.(3)NCP and MNCP were placed in white oil and oil-water emulsion to study the oil-water selectivity of secondary crosslinking plugging agents.The results show:the particles slowly decomposed and degraded,and can not form colloids again in white oil;in the oil-water emulsion,the decomposed particles can not be re-formed,when the oil-water ratio is more than 7:3.The particles can be re-formed after the decomposition,when the oil-water ratio reaches 1:1,but the gel rapid dehydration in 5 days.(4)The reservoir adaptability of particle type secondary crosslinking agent and intercalated particle type secondary crosslinking agent was analyzed.The results show that the former can be resistant to temperature of 130?,salt of 4× 104mg/L in the pH value of 7?10 conditions.And the strength was maintained at code I at 130? and 2 × 104 mg/L after 90 days.The latter can be an anti-130? temperature,salt 21.2×104mg/L,and the strength retention at level I after aging 90 days at 115?,10×104mg/L.(5)SEM scanning shows that the water-shutoff agent gradually decomposed into linear polymer molecules with the failure of the unstable crosslinking agent P-1,which conducted secondary crosslinking reaction with the secondary crosslinking agent after the plugging agent entered the formation,and form a stable network structure.(6)Indoor core simulation experiments show:1)Two plugging agents have a good injection and plugging property,which plugging rate can reach more than 98%.And the blocking rate can still be maintained at more than 96%after 40PV washout.The plugging effect of injection 0.7PV and 1PV is significantly better than injection of 0.5PV.2)The plugging agent has a good oil and water selectivity.And when the permeability heterogeneity exists,the blocking agent is more selective and the oil and water selectivity is better.3)The experiment of fracture model and carve model show:burst water flooding will happen in the water flooding stage.The plugging agent can effectively reduce the water cut and improve the recovery rate. |
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