Research on Wellbore Blockage Mechanism and Blockage Removal Technology of Shale Gas Wells

Abstract With the continuous extension of development time, the production decline of single well is accelerated, and the problem of wellbore blockage in shale gas wells is prominent. The problem of wellbore blockage seriously restricts the stable production and efficient development of gas fields. In this paper, the ‘micro + macro’ analysis method is used to study the blockage. It is found that the wellbore blockage mainly includes corrosion, scaling products and a small amount of clay minerals brought by the reservoir during gas production. In the process of production, corrosion and scaling mechanism work together. Acidic gas such as CO2 in shale gas are dissolved in high-salinity formation water, causing electrochemical corrosion of the string. The formation of corrosion products will promote the deposition and adsorption of inorganic scales. The uneven accumulation of corrosion product films will enhance the surface roughness of the substrate and accelerate the deposition of scale samples around the crystal nucleus. At the same time, scaling will cause corrosion under the scale of the pipe string. Cl − can penetrate into the film through the micropores covering the product film on the metal surface, and pitting corrosion occurs to corrode the pipe string. Finally, the corrosion and scaling products together cause the pipe string to be blocked. Based on the analysis results of blockages and water samples, a blockage removal liquid system was developed according to the blockage mechanism. It has a high dissolution ability and the corrosion of 125SG, 155V and N80 steel sheets at 60°C for 4h is less than 1 g/(m 2 ·h), which meets the requirements of industry standards. This system can inhibit the secondary precipitation of metal ions, has low corrosion damage to oil and casing, can remove wellbore blockage, does not need to flow back, will not cause secondary damage to the reservoir. It can provide guiding significance for similar shale gas well wellbore blockage removal.