The Research On Potential Damage And Acid System Of Ultra-low Permeability Sandstone Reservoir In Shanshan Oilfield

With the increase of global demand for oil and gas resources and the progress of oil and gas exploration and development,the development of ultra-low permeability reservoir has become one of the important areas of oil and gas production.Ultra-low permeability reservoirs are generally characterized by poor reservoir physical properties,serious heterogeneity,and poor reservoir water absorption capacity.Therefore,acidification measures are often used to efficiently excavate reservoir productivity.In the process of reservoir acidizing stimulation,if the acid system is not used properly,it is easy to cause secondary damage to the ultra-low permeability reservoir,resulting in poor acidizing stimulation effect and reduced oil recovery.In order to ensure that the acidification operation meets the effect of increasing permeability and increasing production,and at the same time reduce the secondary damage caused by improper use of acid system to ultra-low permeability reservoirs.Taking the ultra-low permeability sandstone reservoir of Sanjianfang Formation in Shanshan Oilfield of Tuha Basin as the research object,the basic characteristics,potential damage types and damage mechanism of ultra-low permeability reservoir in Shanshan Oilfield were studied by means of XRD diffraction analysis,scanning electron microscopy,gas porosity and permeability measurement,reservoir damage evaluation experiment and field data collation.Based on the basic characteristics and potential damage of ultra-low permeability reservoir,a kind of extensive steering acidification stimulation solution PRS was developed.The acidification stimulation solution can be mixed with the main acid liquid such as mud acid to form a combined acid liquid system.In addition,the external engineering factors of acidification construction are considered.Finally,a combined acid system for protecting ultra-low permeability reservoir is formed.The research results can provide scientific basis for acidizing stimulation of ultra-low permeability sandstone reservoirs.The main research contents and understandings are as follows:(1)The clay minerals of ultra-low permeability sandstone reservoir in Shanshan Oilfield are mainly kaolinite and montmorillonite,belonging to high clay mineral reservoir.The physical properties of the reservoir are characterized by low porosity and extra-low permeability.The pore types are mainly secondary pores,and the pore throat types are mainly small pore throats.Crude oil has the characteristics of "three low and two high",belonging to light crude oil.The reservoir is unsaturated reservoir with normal formation pressure.(2)The ultra-low permeability sandstone reservoir in Shanshan Oilfield has the characteristics of strong stress sensitivity,medium to weak velocity sensitivity,alkali sensitivity,water sensitivity,salt sensitivity and weak acid sensitivity.Clay minerals and pore structure are the important factors leading to the sensitivity damage of the reservoir.In addition,the reservoir has medium to weak water lock,strong Jamin effect,pore throat type is an important factor leading to the reservoir water lock damage.(3)Based on the basic characteristics and potential damage of ultra-low permeability sandstone reservoirs in Shanshan Oilfield,a kind of extensive steering acidification stimulation solution PRS is preferred in the laboratory.The stimulation solution is composed of clay stabilizer,surfactant,chemical diverting agent and rock pore resistance reducing agent.The combined acid system formed by the stimulation solution and soil acid can dissolve large pores,micropores and other scale pores to form a pore network system,which can increase the core permeability of the target reservoir to a maximum of 2.68 times of the original permeability.(4)Considering the external engineering factors in the process of acidizing stimulation,the corrosion inhibitor and iron ion stabilizer were optimized,and the combination acid system formula for protecting ultra-low permeability sandstone reservoir was finally determined: 1.5 % PRS + 10.0 % HCl + 3.0 % HF + 1.0 % NSY-2+ 1.0 % F2326.