Research and Application of Wellbore Fixed-Point Acidification Unblocking Technology for High Temperature and High Pressure Gas Wells

Abstract

In recent years, the high temperature and high pressure gas wells production in Kuqa mountain front zone were severely restricted due to the blockage of the wellbore, which affected the efficient development of gas field group of the Kuqa mountain front. The Dina and Keshen blocks were the main gas fields and the wellbore blockage problem was more severe. The problem in the Keshen gas field was mainly concentrated in the Keshen2 block. More than 50% gas wells had that problem, which leaded millions of square meters of production loss compared with the full production. As for Dina gas field, the problem was severer and more than 80% wells had wellbore blockage problems, which resulted in reducing the gas production by more than half, and even shutting down the production. For the severely blocked wells, the coiled tubing tool was used to unblock and the wellbore blockage sample was finely collected. It could be drawn that the wellbore blockage distribution was partly blocked and blockage position was likely to occur at the reduced diameter throttling tool or the screen pipe. The amount of blockage was less than 30L, and the main component of the blockage was measured as scale. Based on the understanding of the blockage, a "9%HCl+1%HF" acid unblocking liquid system was developed. The dissolution rate of the liquid system to the scale was greater than 90%, and the dissolution rate of the formation sand sample was greater than 34%. For blocked wells with flow passages available in the wellbore, the wellbore fixed acidification was used and the unblocking process was that under the condition of controlling the pump pressure not higher than the maximum allowable pressure of the wellhead, acid unblocking solution was injected at low-displacement to dissolve the wellbore blockage and to restore gas well productivity. Compared with the coiled tubing sand washing, wellbore fixed acidification had the effect of better performance, simple process and low time consumption. A total of 14 wells had a success rate of 100%. After fixed-point wellbore acidification, the single-well oil pressure increases by 30MPa. The amount of gas production was increased by 207×104 m3/d, and the open-flow capacity of 71% wells was equal or exceeded to the capacity at the initial production stage.