What is the workover process like?

Oil and gas wells are often "sick" during production and need different medical skills to treat them. Among them, treating a serious illness is called "overhaul". When oil and water wells are overhauled, the technical condition of the wellbore is generally complicated. Before the operation, the technical condition of the shaft must be carefully implemented according to the operation content, and the effective maintenance should be carried out to prevent the technical condition of the shaft from further deterioration. The main process is as follows:

(1) drifting.

Drifting is an effective method to detect casing integrity and whether there are foreign bodies (fish falling, sand plugging, wax plugging and salt plugging) in the wellbore. Usually, the standard caliper is used to size the borehole. When the running tool exceeds the standard drift gauge, the drift gauge size can be determined according to the maximum geometric size of the running tool; Or dredge the well with simulation tools. When the well is blocked, it means that there is something wrong with the wellbore conditions, which should be further verified by printing or logging.

(2) Scrape and clean the shell.

The purpose of scraping and washing casing is to remove cement, wax, various scales and burrs on the inner wall of casing, so as to ensure the normal operation of running tools and the successful setting of packer. At present, there are two kinds of casing scrapers used in China: rubber cylinder type and spring type.

(3) well washing.

The purpose of well washing is to clean the wellbore.

(4) Engineering logging detection casing.

Engineering logging is to detect the technical condition of casing with logging instruments. Commonly used logging methods include caliper logging, well temperature logging, continuous flow logging, isotope logging, color ultrasonic television imaging logging, casing residual wall thickness logging and cement bonding logging.

(5) The printing method is used to check the technical status of the borehole.

Printing inspection is to verify the state and geometry of casing and fish head by using impression (including lead mold, rubber mold, wax mold, etc.) ), and then make qualitative and quantitative analysis to determine their specific shapes and sizes. The impression method is suitable for checking the geometric shape, size and depth of the fish head of downhole objects, verifying the casing damage degree such as casing deformation, dislocation and rupture, and the technical status of the wellbore that needs to be temporarily ascertained during operation and workover.

(6) Pressure test.

In principle, the pressure test pressure should be equal to 1.2 times of the maximum working pressure, 1.3 times for water injection wells and 1.4 times for gas injection wells. After 30 minutes, the pressure drop is less than 0.5 MPa, which is qualified. If the pressure test can't be conducted, it is necessary to find out the reason and take further measures according to the leakage amount and leakage position.

In addition, there are fishing operations, stuck release operations, sidetracking, changing well types and engineering scrapping of wells.