The North Kuwait (NK) Development Plan calls for rapid increase in NK production, mainly through the implementation of waterflooding in NK major reservoirs. The new production profile incorporates increased water production and, based on corrosion prediction models, results in elevated corrosion rates in down-hole completion equipment. This predicted increased corrosion has already become a reality in the past three years. Severe down-hole corrosion in production and injection wells has resulted in tubing and casing failures and severe casing/tubing corrosions. Remediation of these wells has resulted in problematic, high cost workovers, and in one case, the loss of the productive interval and the associated reserves.
To manage current and future corrosion in NK, an extensive corrosion-monitoring program has been implemented to initially identify the extent of corrosion in the current well stock and then to adopt corrosion prevention strategies to mitigate the problem and reduce the associated cost and production impact. The down-hole internal corrosion monitoring effort is one of the first steps in implementing the NK Corrosion Management Plan.
This paper discusses the results of the program to date and describes the diagnostic tools used to effectively monitor the extent of down-hole corrosion in North Kuwait. Different tools such as the caliper, MicroVertiLog tool (MVRT), and surface inspection methods have been utilized to quantify down-hole corrosion. The paper also compares MVRT tool response with caliper and surface inspection data in an effort to ensure down-hole corrosion detection corresponds with results measured at surface. This will allow immediate corrective action to be taken for the completions based on down-hole log results.
Introduction
First commercial oil production from North Kuwait started back in 1955. According to the Kuwait Oil Company (KOC) production database, production of crude oil with watercut in North Kuwait started in the mid 1980's as water-handling facilities became available. However, the water production was in insignificant quantities.
Down-hole corrosion was not a major issue up to late 1990's due to low or no watercut in most of the wells. In addition, the corrosion problem was indirectly managed through the process of converting wet producers to dry production by applying down-hole water shut-off techniques. The water shut-off (mostly carried out by a rig workover operation) was necessary to allow maximum oil production through the then existing facilities with limited water handling capacity. However, lately, with the increasing water production and water handling capacity in North Kuwait, corrosion has become an important issue. With the implementation of the current development plan, which includes waterflooding of several major reservoirs, down-hole corrosion needs to be managed properly to avoid severe production and operating cost impacts. Corrosion in North Kuwait will impact the whole production and processing stream. This paper, however, only discusses the down-hole tubular corrosion issues.
Causes of Down-hole Corrosion In North Kuwait
Although this issue needs to be fully investigated and confirmed, the cause of current down-hole corrosion in North Kuwait fields is suspected to be mostly the CO2 in the formation water. The dissolved CO2 in the formation water is assumed to result in the formation of carbonic acid (H2 CO3), which reacts with metal and causes corrosion. The pH of most of the reservoir waters in North Kuwait is acidic (between 5.5–6.5). In addition, the high salinity of the formation water reduces the formation/presence of the protective film on the tubing wall and exposes the tubing to corrosion. We note a strong correlation between cumulative water production and severity of corrosion in most of the wells. This leads to support the hypothesis of CO2-induced corrosion. With the implementation of seawater injection in Mauddud, Upper Burgan, and Zubair reservoirs, the cause of future corrosion is expected to include other factors as well.
