Saudi Arabia embarked on an aggressive development of new gas fields to meet the increasing demand for natural gas and gas condensate. Therefore, it became necessary to further develop gas reservoirs. However, the reservoirs presented challenging conditions such as temperatures up to 275°F, H2S contents up to 10 mol% and CO2 contents higher than 2 mol%. Previous completions utilized regular low-carbon steel (L-80 and C-95) metallurgy. Due to the nature of the reservoir conditions, these types of completion hardware could not be applied in areas where H2S content is very low and CO2 is high. Super 13Cr completions have been proven to be reliable in these environments. However, Super 13Cr completions cannot tolerate the high acid concentrations (28 wt% HCl Acid) that are needed to acid fracture the tight carbonate formations available in Saudi Arabia. Therefore, a special acid blend and corrosion inhibitor package had to be developed to effectively stimulate the carbonate formation through these types of completions. This paper will present how the aforementioned problem was overcome by developing an acid blend using 15 wt% HCl and 9 wt% formic acid. Initial laboratory tests showed high corrosion rates for the Super 13Cr coupons when this acid formulation was applied. However, due to an intensive research effort, an effective corrosion inhibitor package was developed for Super 13Cr completions using this acid system. Several corrosion inhibitors and inhibitor aids were tested. Compatibility of various additives was conducted and corrosion tests were performed at bottom-hole conditions. As a conclusion, a new corrosion package was developed for Super 13Cr tubing. This package is compatible with reservoir fluids and other acid additives. In addition, it produces acceptable corrosion rates with no pitting. Introduction Acid Fracturing Background The main objective of a stimulation treatment is to increase the rate at which the formation delivers hydrocarbons naturally. Fracturing treatments are defined as treatments where the injection rate of the fluid is greater than the fluid leak-off into the matrix of the formation. The pressure in the wellbore will therefore build up and eventually lead to tensile failure of the rock creating a conductive channel. The addition of acid in treatments for carbonate formations will create a conductive channel due to the reactive nature of the fluid. The aim is to change the future flow pattern of the reservoir from radial to linear in order to effectively stimulate the reservoir and increase the production. The first hydraulic fracturing treatment was performed in 1949. Since then, hydraulic fracturing has done more to increase recoverable reserves than any other technique. Proppant fracturing is the most common method in North America since most formations observed are sandstone formations. However, due to the fact that most formations in the middle east are carbonate formations, acid fracturing is more common in these countries such as Bahrain and Saudi Arabia.1–5 Therefore different challenges, such as corrosion of tubulars and increased fluid leak-off, have to be addressed. The Saudi Arabian Non-Associated Gas Field Development Saudi Arabia is the largest oil producer in the world and has an estimated oil reserve of 25% all proven oil reserves in the world. Therefore, in the 1970's, Saudi Arabia developed a national strategy which stated, that energy needed for the countries industry will be produced by using these reserves. However, in recent years it has become obvious that gas is an attractive alternative to oil due to the following reasons:It is more environmentally friendlyLNG Plants have to be constructed in order to export gasthe usage of gas to produce the required energy frees up oil for exports Acid Fracturing Background The main objective of a stimulation treatment is to increase the rate at which the formation delivers hydrocarbons naturally. Fracturing treatments are defined as treatments where the injection rate of the fluid is greater than the fluid leak-off into the matrix of the formation. The pressure in the wellbore will therefore build up and eventually lead to tensile failure of the rock creating a conductive channel. The addition of acid in treatments for carbonate formations will create a conductive channel due to the reactive nature of the fluid. The aim is to change the future flow pattern of the reservoir from radial to linear in order to effectively stimulate the reservoir and increase the production. The first hydraulic fracturing treatment was performed in 1949. Since then, hydraulic fracturing has done more to increase recoverable reserves than any other technique. Proppant fracturing is the most common method in North America since most formations observed are sandstone formations. However, due to the fact that most formations in the middle east are carbonate formations, acid fracturing is more common in these countries such as Bahrain and Saudi Arabia.1–5 Therefore different challenges, such as corrosion of tubulars and increased fluid leak-off, have to be addressed. The Saudi Arabian Non-Associated Gas Field Development Saudi Arabia is the largest oil producer in the world and has an estimated oil reserve of 25% all proven oil reserves in the world. Therefore, in the 1970's, Saudi Arabia developed a national strategy which stated, that energy needed for the countries industry will be produced by using these reserves. However, in recent years it has become obvious that gas is an attractive alternative to oil due to the following reasons:It is more environmentally friendlyLNG Plants have to be constructed in order to export gasthe usage of gas to produce the required energy frees up oil for exports
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSaudi Arabia embarked on an aggressive development of new gas fields to meet the increasing demand for natural gas and gas condensate. Therefore, it became necessary to further develop gas reservoirs. However, the reservoirs presented challenging conditions such as temperatures up to 275ºF, H 2 S contents up to 10 mol% and CO 2 contents higher than 2 mol%. Previous completions utilized regular low-carbon steel (L-80 and C-95) metallurgy. Due to the nature of the reservoir conditions, these types of completion hardware could not be applied in areas where H 2 S content is very low and CO 2 is high. Super 13Cr completions have been proven to be reliable in these environments. However, Super 13Cr completions cannot tolerate the high acid concentrations (28 wt% HCl Acid) that are needed to acid fracture the tight carbonate formations available in Saudi Arabia. Therefore, a special acid blend and corrosion inhibitor package had to be developed to effectively stimulate the carbonate formation through these types of completions. This paper will present how the aforementioned problem was overcome by developing an acid blend using 15 wt% HCl and 9 wt% formic acid. Initial laboratory tests showed high corrosion rates for the Super 13Cr coupons when this acid formulation was applied. However, due to an intensive research effort, an effective corrosion inhibitor package was developed for Super 13Cr completions using this acid system. Several corrosion inhibitors and inhibitor aids were tested. Compatibility of various additives was conducted and corrosion tests were performed at bottom-hole conditions. As a conclusion, a new corrosion package was developed for Super 13Cr tubing. This package is compatible with reservoir fluids and other acid additives. In addition, it produces acceptable corrosion rates with no pitting.
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