Study On Non Acid Blockage Removal Technology Of Low Porosity Fractured Gas Reservoir

The target block is a typical low porosity fractured reservoir,which has the characteristics of ultra deep,high temperature,high pressure,low porosity,low permeability,large reservoir thickness,and the development of natural fractures.The natural fractures are full or half filled with calcite and mud.Due to high pressure reservoir,in order to ensure the safety of drilling,a lot of barite are often added to the drilling fluid as weighting agent to balance formation pressure.Because of the bottomhole pressure difference and pressure disturbance caused by tripping,the drilling fluid is easily leak into the natural fractures.After long-term deposition and aging,a large number of barite and other solid particles form a serious blockage in the fractures,resulting in low natural gas production capacity.Therefore,it is necessary to stimulate the reservoir formation.The stimulation measures used in the early stage of the target block have a great difference in effect.Acidification and acid fracturing can not effectively dissolve barite,and caused serious corrosion of downhole string.And many problems happened when using sand fracturing,such as the serious loss of fracturing fluid,the difficulty of adding sand and the high pressure of construction.In view of the difficulty of stimulating low porosity fractured reservoir,the idea of non acid blockage removal technology is proposed in this paper.The main works are as follows:(1)Based on the analysis of the geological characteristics and the earlier stage stimulation measures of the reservoir,the characteristics of the reservoir and the requirements of the stimulation measures are defined,and the basic idea of non acid blockage removal is established.(2)Through interior experiment and CFD numerical simulation,the main controlling factors of drilling fluid damage degree in fractured reservoir are systematically analyzed,the characteristics and extent of injury and the extent of injury were defined,which provided the basis for the development of the subsequent blockage removal scheme.(3)A non acid blockage removal agent with infiltration,dispersion and chelation is selected based on theoretical analysis and experimental means.The mechanism of blockage removal agent under different conditions was revealed from the influence of pH value,concentration of auxiliary agent,concentration of main agent,reaction time,reaction temperature and calcium magnesium scale on the blockage removal performance.A set of non acid blockage removal fluid system is formed by combining the characteristics of the target reservoir and screening a variety of additives,and the effectiveness of this system was evaluated by interior dynamic experiments.The results show that the dissolution ability of barium sulfate is above 15g/L,and the final permeability of barium sulfate damaged core recovered 240%and 500%.The non acid blockage removal fluid system can effectively relieve the blockage of barite and satisfy the requirements of construction site.(4)A set of non acid blockage removal construction scheme suitable for the target reservoir is formulated according to the preliminary simulation and experimental results.The B84 well is verified on the spot,and the daily gas production increased from 15×104m3 to 70×1043?80×104m3 after the blockage removal operation,which verifies the reliability of the system and process.The research contents and achievements of this paper have a good adaptability to the stimulation of the target reservoir.The non acid blockage removal technique can effectively remove the barite blockage,with unique advantages of very low corrosion to ensure wellbore integrity.The technique provides a useful research method and technical ideas for the efficient development of similar reservoirs.