| Situated at Karamay oil field’s 94 district,the oil block of Qigu formation is characterized by active bottom water with obscure barriers and interbeds.Impaired by continuous propulsion of bottom water during steam driving,large porous channels have been fonned at the bottom of oil layer and the water cone,some oil wells have been appeared serious water flooding and high water cut as well as low recovery degree.At the same time,The severe sand production and steam breakthrough at the process of production because of the unconsolidated sandstone,leading to badly flooding and low development efficiency.Therefore,considering certain geological features and exploitation situations,a series of artificial barrier water plugging technologies,involving urea fonnaldehyde resin plugging agent,have been proposed in this paper.As an effective chemical water plugging method,the artificial barrier water plugging technology can withhold coning from bottom water to wells and change the directions of bottom water flowing around wells,contributing to lower water-cut and higher oil-cut.With the aid of urea fonnaldehyde resin’s thermosetting property,the water plugging system proposed in this paper can demonstrate satisfactory injection capacity due to its low initial viscosity.As a result,the plugging system can be easily adaptable to reservoirs featured by high temperature,low fracture pressure and unconsolidated sandstones and can be effective to plug bottom water.Based on a series of experiments,the optimized artificial barrier water plugging system appropriate to the 94 district has been selected with related performance evaluations.The optimal composition of the plugging agent can be summarized as 40%of urea formaldehyde resin solution concentration,800g/L of solidified agent concentration and 500～400mg/L of regulator agent concentration.Moreover,the initial viscosity of this system should be 8.0mPa s(equal to 7.34S-1 at ambient temperature),and the curing time should be restricted to 27～62h with wide regulation ranges and high consolidation strength,and it can be adjusted according to the requirements of the oil field.The experimental results show that the system has good temperature tolerance,brine tolerance and stability,and can well adapt to the reservoir environment.Additionally,sealing characteristics,flushing resistance as well as injection capacity has also been tested and analyzed by means of core flow experiments.The experiments of breakthrough pressure gradient in average permeability sand-filled pipe is 9.2MPa/m,and plugging rate reaches to 99.2%,which suggest that the plugging agent system has great sealing characteristics.The plugging agent system has a good injection and stability performance with low injection pressure,which is 0.17MPa,under continuous injections.After a amount of 10PV water injection volume,the plugging efficiency is still as high as 98.2%,indicating that the plugging agent system has a good performance of flushing resistance.Apart from that,visual physical models have been designed and made iln order to analyzc and discuss theories for artificial barrier water plugging and relevant influcntial factors.Equipped with all above experiments and analysis,an artificial barrier water plugging scheme for typical wells 94902 in the block has been designed eventually.The research results concluded in this paper can offer theoretical assistance for guiding recovery enhancement for the oil block with bottom water in the 94 district,and can provide useful experiences for similar reservoirs in terms of plugging water. |
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