Mechanism And Removal Method Of High-Maturity Bitumen Damaging Carbonate Reservoir

Carbonate reservoir plays an important role in oil and gas production all over the world,and efficient exploitation of carbonate reservoir is of great significance.As an associated product of oil and gas,reservoir bitumen is widely distributed in carbonate rocks,its existence will lead to the decrease of reservoir physical properties and affect oil and gas production.At present,the removal of low maturity bitumen mostly uses organic solvent and the principle of similar phase dissolution,while the removal of high maturity pyrobitumen and its damage to carbonate reservoir are less studied.It is of great practical significance to study the damage mechanism and removal method of carbonate reservoir with high maturity bitumen for reducing the damage of pyrobitumen and efficient development of carbon gas reservoir.Based on the study of the basic physical properties,bitumen content,rock components,pore structure and the characteristics of the reservoir bitumen,this paper studies the influence of bitumen on the physical properties,fracture permeability and conductivity of the reservoir,and uses sodium hypochlorite solution to remove the pyrobitumen.This paper describes the porosity and permeability characteristics,asphalt content,rock composition and pore structure of Longwangmiao formation reservoir in Longnvsi area.The experimental results show that the bitumen content in the study area is rich,accounting for 2.71% of the total mass,and the correlation between porosity and permeability is poor,dolomite is the main mineral in the rock sample.The experimental rock samples mainly develop ultra micro pores with pore diameter less than 1 ?m.The microscopic and chemical characteristics of the bitumen in the study area are clarified.By means of thin section observation,maturity test,scanning electron microscopy,X-ray diffraction and other experimental means,the occurrence,maturity,micro morphology and source of reservoir bitumen were analyzed.The results show that the bitumen in the carbonate reservoir of Longwangmiao formation in Longnusi area comes from the Lower Cambrian source rock;the bitumen is in the over mature stage and belongs to the pyrobitumen of thermal evolution origin.The condensed degree of the condensed ring compounds is higher and tends to be oriented;it is mainly filled in stylolite,intercrystalline pores and dissolved pores/holes.The damage degree of pyrobitumen to carbonate reservoir is evaluated.The results show that the bitumen in the reservoir occupies part of the reservoir space,blocks the seepage channel,reduces the porosity of the reservoir,and at the same time reduces the permeability of the reservoir;it is easy to form insoluble free bitumen after acid pressing transformation,and the acid corrosion fracture is blocked,which causes serious damage to the conductivity.The method of using sodium hypochlorite to remove carbonaceous asphalt is put forward.When the concentration of sodium hypochlorite solution is 20%,the treatment temperature is 90 ?,and the treatment time is 12 hours,the removal rate of pyrobitumen is 15.01%;the porosity,permeability and fracture conductivity can be improved to some extent by using this method.After sodium hypochlorite solution treatment,the particle size of asphalt decreased,the-OH group increased,and the vibration caused by aromatic ring skeleton weakened,indicating that sodium hypochlorite solution oxidized and removed part of pyrobitumen.