Challenging HPCT Scale Removal Operations in High H2S Environment Successfully Completed with Interdisciplinary Job Design and Execution

Abstract

The carbonate gas producing zones of the Ghawar field have been impacted by extensive FeS scale deposition, reducing overall gas production and significantly increasing risks of well interventions. Previous remediation included the use of workover rigs which can be costly due to time required for workover and lost production. H2S levels (2-7%) found in the reservoir also contribute to higher costs and risks when using workover rigs. Different chemical solutions have been utilized in similar cases and also considered for these wells, but the FeS could not be 100% dissolved with either HCl, DPTA, EDTA, GLDA blends. These chemical blends generate large amounts of H2S in addition to the already existing high levels of H2S in the formation gas. Additionally, the completion tubulars and CT were adversely affected by chemical reaction and corrosion. This poses a safety concern having large amounts of H2S in returns at surface along with potential chemical corrosion. Therefore, the safest and most economical method was to devise an effective mechanical descaling solution with CT. This paper will discuss two case histories where mechanical descaling utilizing CT was applied. Each well had major challenges that included low reservoir pressure, increased reservoir temperature, scale with high specific gravity (3.7 to 4.3), and in the second case, horizontal open-hole sections. The low reservoir pressure required isolation methods to allow for returns to circulate out the heavy scale and to minimize fluid losses to the formation. Following mechanical descaling with CT, the final challenge discussed in the paper is bringing the well back to maximum gas production using HPCT cleanout optimization and HPCT stimulation techniques.