Field Application of HCl-Formic Acid System to Acid Fracture Deep Gas WellsCompleted with Super Cr-13 Tubing in Saudi Arabia

摘要

This paper describes optimization of gelled and in-situ gelledrnHCl/formic acid systems to stimulate deep gas wellsrncompleted with super Cr-13 tubing. High temperaturesrnencountered in deep wells and the susceptibility of super Cr-rn13 to severe corrosion by concentrated HCl solutions and highrnchloride ion concentrations render acid stimulation a veryrndifficult task. Therefore, extensive experimental and fieldrnstudies were performed to develop a cost effective acid systemrnto enhance the productivity of deep gas wells, whilernmaintaining the integrity of the super Cr-13 tubing.rnCoreflood tests indicated that this acid system can createrndeep wormholes in tight reservoir cores (less than 1 md).rnCorrosion tests, however, indicated that protecting super Cr-13rntubulars during pumping this acid (15 wt% HCl/9 wt% formicrnacid) is not an easy task, especially at downhole temperaturesrn(275oF). A very limited number of inhibitor aids were foundrnto be effective in protecting super Cr-13 at reservoirrnconditions. To optimize the corrosion inhibitor package, thernbottom hole temperature was measured in a few wells duringrnacid injection.rnBased on lab tests and field measurements, an acidrntreatment was designed and applied in the field. The treatedrnwells responded positively to the treatment. Most importantly,rnthe integrity of the super Cr-13 was maintained. This wasrnconfirmed from chemical analysis of well flowback samplesrnfollowing the treatment and measurement of the tubing insiderndiameter before and after the treatment. The maximum Crrnconcentration in the flowback sample was less than 2 mg/L.rnMolybdenum and nickel concentrations were less than 1 mg/L.rnThe total iron concentration was less than 200 mg/L. Thisrnvalue is significantly less than that noted with wells completedrnwith low-carbon steel tubulars.