Have you ever asked yourself why we do cementing job? Well, cement is very important in well drilling as it provides a good protection for your well and environment.
- Cement provides a good isolation for your well preventing fluids from travelling out and in the well. As it makes zonal isolation in which no fluid migration up or down, preventing fresh and salt water zones connection.
- Cement seals off thief zones that causes loss of circulation.
- Cement protects casing from corrosive fluids such as salt water.
- Cement is used also to plug a depleted zone, abandonment well and sidetracking.
After 3D seismic data is acquired, it needs to be processed to be ready for interpretation as the image is blurred. Data processing includes filtering, stacking and migrating and other forms of computer analysis. As computers have become more powerful and processing techniques more developed, it has become common to re-process seismic data acquired in earlier years, creating new opportunities for exploration that could not originally be derived from the 3D data. Processing of one 3D seismic survey may take months and cost a lot of money.
- Guide Shoe
- After drilling the section, we run the casing into the hole. For example, if we drilled a surface hole 17.5-in, the casing will be 13 3/8-in to provide a good clearance for cementing job. In the bottom joint of the casing there is an accessory named by “guide shoe” which is made of steel and concrete as it will be drilled after finishing the job. The shoe is used to provide an ease of movement for the casing string between debris.
- Float Collar
- Another accessory is “float collar” which is made also from steel and concrete and is used to prevent mud from interring the casing as it has a valve which is one-way valve. It provides a receptacle for cement plugs. It is installed after two joints form the bottom.
- Float Shoe
- Sometimes, float shoe is used instead of float collar and guide shoe. It is like a guide shoe with one-way valve.
- Centralizers and Scratchers
- Also centralizers and scratchers are installed outside the casing. Centralizers helps to keep the casing in the center of the hole which in its turn increase the efficiency of cementing job and makes a good distribution of cement around the casing. Scratchers helps to clean the hole from mud as it makes the formation surface rough enough for cement to stick to it.
- Bottom Plug
- Cementing wiper plugs are used for preventing different fluids mixing. We install the bottom plug then, the top plug. The bottom plug is used to separate between drilling mud and cement and to clean casing from mud. After it reaches the float collar or float shoe. The cement pumping pressure should be increased to tear the rupture disk. Then cement flow up to the surface through annulus.
- Top Plug
- After pumping the calculated quantity of cement the top plug is installed to separate mud from displacement fluid (water or drilling mud) and cleaning the casing from cement.
- Cementing Head
- Cementing Head is a valve that is installed on the rig floor on the top joint of the casing. It is hanged by the elevator in the rig floor this valve enables to install both of the bottom and top plugs. Cement slurry enters the casing from this valve.
- The crew drills the surface hole (ex. 17 ½") to the determined depth.
- Then, tripping out from the hole by using washing and reaming.
- If problems encountered use back ream, but it is not favorable because it causes damage to the hole.
- After tripping out, it is the circulation turn in order to clean the hole.
- Use 13 3/8" casing to give a good clearance for cement. Use casing collar to make connections.
- Rig up 13 3/8" casing power tong, spider and elevator. Power tong is used to make casing connections. Spider and elevator are used to hold casing in position with cementing head.
- Cementing head is installed in position as shown in figure below.
- Starting with pumping spacer fluid (fresh water) to clean the casing and hole from mud.
- It is the turn of cement equipment that is responsible for mixing cement components and pumping them to the cementing head. Recirculating cement mixer is used to mix cement, water and chemicals. Special pumps are used to pump cement slurry to the cementing head.
- Before cement slurry reaches the cement head the bottom plug is released. Then, cement slurry pushes it down till it seats at the float collar. With the increase of pumps pressure the rupture disk teared making slurry to migrate up through annulus.
- After pumping the calculated quantity of cement slurry, top plug is released. Then, displacement fluid is pumped to the casing until gauges read a large increase in pressure that means the top plugs is seated above the bottom plug.
- After pumping all cement slurry, cement needs time to harden that is named by wait on cement(WOC). WOC varies between 12 to 24 hours.
- Cement is tested by cement bond log(CBL) to check its efficiency.
- When WOC and tests ended, the welder cuts the conductor above the surface.
- The crew nipples up the BOP stack on the surface casing. Pressure tests are run to make sure that it works properly.
- The well is ready to drill the intermediate hole and nearly, the same steps are done till completing the well drilling.
Cement is so important in drilling process as it helps to keep the hole stable and suspend the casing in position. so that this job need to be done perfectly for many reasons may be the main reason for the operator is to isolate thief zones. It also helps to prevent water oil mixing from different formations.
- Halliburton cementing student workbook
- Nontechnical guide to petroleum,exploration, drilling and production –third edition-Norman J. Hyne, Ph.D.
- Case study of Schlumberger cementing job at EHO ALAlamain Concession EDC rig No.60