CORROSION PROBLEM DURING ACIDIZATION IN OIL WELLS AND THEIR REMEDIAL STEPS
Dr. S. Vishwanathan Sir
Dept. of Applied Chemistry
Admn. No. 9520 Semester Vth
B. Tech. Petroleum Engineering
Methods of acidization
Corrosion during acidization job
- Acid corrosion (causes and mechanism)
Remedial steps to reduce corrosion
- Use of Arcasolve™ in Acidizing Processes
- Use of corrosion inhibitors
Acid treatments have been applied to wells in oil and gas bearing rock formations for many years. Acidizing is probably the most widely used work-over and stimulation practice in the oil industry.
By dissolving acid soluble components within underground rock formations, or removing material at the wellbore face, the rate of flow of oil or gas out of production wells or the rate of flow of oil-displacing fluids into injection wells may be increased.
Corrosion remains a major challenge to maintaining the integrity of both newly built as well as ageing facilities to cope with the escalating oil and gas production. The increasing use of secondary oil recovery has raised the levels of reservoir souring and water cut, thus necessitating more intricate material selection and corrosion control. The greatest challenges are at the subsurface level where environments are more severe and operational procedures, such as acidizing and cementing, have a greater impact on corrosion.
TYPES OF ACIDIZATION
Two primary requirements that an acid must meet to be acceptable as a treating fluid: (1) it must react with carbonates or other minerals to form soluble products, and (2) it must be capable of being inhibited to prevent excessive reaction with metal goods in the well.
Two basic types of acidizing operations can be conducted:
Sandstone matrix acidizing, employing mud acid systems, is a common operation in oil and gas fields. Matrix acidizing involves the use of acid injected at below fracture pressure. The main objective of this stimulation operation is 1. To remove near wellbore damage, caused by drilling and/or work-over operations, 2. To restore or, perhaps improve the permeability of near-wellbore formation. Typically, sandstone matrix stimulation involves three stages: (1) a pre-flush stage where an aqueous solution of HCl is injected to displace formation brine and dissolve any carbonates that may be present, (2) a mud acid treatment to dissolve silicious and damaging material, and (3) an after-flush where a solution of HCl is injected to displace the reaction products. Mutual solvents have been also used in the latter stage to restore wettability. Fracture acidizing, also known as acid fracturing is the most widely used acidizing technique for stimulating limestone or dolomite formations. In an acid fracturing treatment: A pad fluid is injected into the formation at a rate higher than the reservoir matrix will accept. This rapid injection produces a build-up in wellbore pressure leading to cracking (fracturing) of the rock. Continued fluid injection increases the fracture's length and width. Acid (normally 15% HCl) is then injected into the fracture to react with the formation and create a flow channel (by etching of the fracture surface) that extends deep into the formation. This allows more reservoir fluid to drain into the wellbore along the new fractures once the well is put back on production.
Acid antisludge additives are used to prevent sludge formation from crudes containing asphaltenes and iron, which occurs when asphaltenes and iron are encountered or introduce through the treatment. Asphaltene solvents solubilize deposits. There are also inhibitors available to aid in the prevention of those deposits. Dispersants are used to keep...
Please join StudyMode to read the full document