Research On The Adaptability Of Molecular Membrane Injection Technology In Low Permeability Reservoirs

With the development of oil and gas resources,most of the onshore oil fields with high-medium permeability have entered the middle-late development stage in China.And,the stable production situation of oil fields is tense increasingly.Thus,it is great significance to utilize and develop the low permeability reservoirs for the sustainable and stable development of China's petroleum industry.However,in the process of waterflood displacement,it is easy to produce the problem of "no injection,no production".In the development of low permeability reservoirs with baikouquan reservoir as an example.the decompression and augmented injection of water injection wells were implemented by using molecular deposition(MD)film injection technology.There were 4 effective wells and 2 wells had poor effects among 6 test wells,which made MD film difficult to popularize and apply in low permeability reservoirs.Therefore,this paper takes baikouquan reservoir as an example to study the adaptability of MD film injection technology in low permeability reservoirs.Firstly,this paper analyzed the under-injection reasons of water injection wells combining with reservoir characteristics,field construction and indoor research,including:1.reservoirs characteristics:low permeability,low porosity,large proportion small throat,poor reservoir matrix physical properties.2.the clay mineral content was relatively large in reservoir,which was prone to hydration and expansion during long-term water injection development.Thus the hydration and expansion had potential sensitive damage.3 Based on the above two points,when the continuous oil flow passing through the pore throat of rock in waterflood development,the capillary force increased sharply.Moreover,the driving pressure was not enough to offset the capillary force,which will cause water lock damage.Therefore,it was easy for low permeability reservoirs to be "no injection,no production" in waterflood development by above three reasons analyses.According to the analysis of the under-injection reasons in the water injection wells,not only the MD film agent was needed as the main agent,but also an acid solution was selected as the pretreatment fluid to ensure that the subsequent treatment agent can be injected into the formation.An anti-swelling fluid was selected to prevent potential sensitive damage for the reservoir.A pre-film solution was selected to provide a beneficial environment for the adsorption of the MD film agent on the rock surface.First of all,a MD-S of small quaternary ammonium salt type was synthesized from N,N,N',N'-tetramethylenediamine and DMC,and the target product was determined by infrared NMR characterization.And its basic performance was tested.The results showed that MD-S was a non-surface-active material with certain surface activity property,and has certain clay anti-swelling effect.When the MD-S concentration being 600mg/L,a stable state of the anti-swelling effect mean that anti-swelling rate did not increased with the increase of concentration.The static adsorption experiment indicated that the MD-S was reached adsorption equilibrium on the rock surface about 12h.The adsorption capacity was 4.0 mg/g,and was relatively small.At the same time,the MD-S made the contact angle of the rock from the original 37.15° to 91.68°.the wettability of rock changed from hydrophilic to weak hydrophilic or neutral wettability.Moreover.MD-S has good compatibility in different concertration sionic solution.The two acid solution concentration systems of 8%HC1+2%HF and 10%HCl+2%HBF4 were screened as the pretreatment solution with the dissolution rate as the index.Finally,8%HCl+2%HF was selected as the preflush fluid with the injection effect as the index in this paper.The anti-swelling agent DF-Y was selected,and the concentration of DF-Y was 2%with anti-swelling rate and viscosity as the index.The NH4Cl was selected as the pre-membrane solution with the depressurization rate as the index.The core flow simulation experiment and nuclear magnetic resonance study suggested that when the water flooding velocity being 0.05?0.10mL/min,the permeability change of the rock sample that was treated by the MD film injection system was the maximum K2/K1=28.93?27.93.The peak was shifted to the left in T2 NMR spectrogram,the irreducible water saturation was reduced,and the T2 cutoff value was reduced.The results proved that the MD film injection system had a good effect of decompression and augmented injection.In addition,the treated rock samples could still be injected at a relatively low pressure under the condition of high speed,large volume and a long time of water flow,which manifested that the rock samples treated by MD film had a good erosion resistance stability.According to the distribution change of water-bearing porosity proportion in the pores of rock samples,the adaptive range of the MD injection system in low permeability reservoirs was determined in this paper:the MD film had obvious effect of decompression and augmented injection in the pore radius greater than range of 0.015?0.02 ?m.And the effect of molecular film system was best in the range of(0.015?0.02)?m?(0.10?0.20)?m pore radius.