- Once a well has been drilled, the decision must be made either the well will be a producer or plugged and abandoned as dry hole.
- Should the operator decide to move forward with developing the well, completion operations must be undertaken.
- Well completion include the steps taken to transform a drilled well into a producing one.
- These steps include casing, cementing, perforating, gravel packing and installing a production tree.
- 1st step is to case the hole. After a well has been drilled, should the drilling fluids be removed, the well would eventually close in upon itself.
- Casing ensures that this will not happen while also protecting the well stream from outside incumbent, like water or sand.
- Consisting of steel pipe joined together to make continuous hollow tube, casing is run into the well.
- The different levels of the well define what diameter of casing will be installed.
- Referred to as a casing program, the different levels include production casing, intermediate casing, surface casing and conductor casing.
- Additionally, there are two types of casing that can be run on a well. One type of casing consists of a solid string of steel pipe. Solid casing is run on the well if the formation is firm and will remain that way during the life of the well.
- Should the well contain loose sand that might infiltrate the wellstream, the casing is installed with a wire screen liner that will help to block the sand from entering the wellbore.
- The next step in well completion is cementing the well.
- This includes pumping cement slurry into the well to displace the existing drilling fluids and fill in the space between the casing and the actual sides of the drilled well.
- Consisting of a special mixture of additives and cement, the slurry is left to harden, sealing the well from non-hydrocarbons that might try to enter the wellstream, as well as permanently positioning the casing into place.
- 2 type of completion: (1) open-hole (2) cased-hole completion
- An open-hole completion refers to a well that is drilled to the top of the hydrocarbon reservoir.
- The well is then cased at this level, and left open at the bottom. Also known as top sets and barefoot completions, open-hole completions are used to reduce the cost of casing where the reservoir is solid and well-known.
- Cased-hole completions require casing to be run into the reservoir.
- to achieve production, the casing and cement are perforated to allow the hydrocarbons to enter the wellstream.
- This involves running a perforation gun and a reservoir locating device into the wellbore, many times via a wireline, slickline or coiled tubing.
- Once the reservoir level has been reached, the gun then shoots holes in the sides of the well to allow the hydrocarbons to enter the wellstream.
- The perforations can either be accomplished via firing bullets into the sides of the casing or by discharging jets, or shaped charges, into the casing.
- While the perforation locations have been previously defined by drilling logs, those intervals cannot be easily located through the casing and cement.
- To overcome this challenge, a gamma ray-collar correlation log is typically implemented to correlate with the initial log run on the well and define the locations where perforation is required.
- Some wells require filtration systems in order to keep the wellstream clear of sand.
- In addition to running a casing with a liner, gravel packing is used to prevent sand from entering the wellstream.
- More complicated than cementing a well, gravel packing requires a slurry of appropriately sized pieces of coarse sand — or gravel — to be pumped into the well between the slotted liner of the casing and the sides of the wellbore.
- The wire screens of the liner and the gravel pack work together to filter out the sand that might have otherwise entered the wellstream with the hydrocarbons.
- The last step in completing a well, a wellhead is installed at the surface of the well.
- called a production tree or Christmas tree, the wellhead device includes casing heads and a tubing head combined to provide surface control of the subsurface conditions of the well.
- offshore wells can be completed by two different types of trees: dry and wet trees.
- Similar to onshore production trees, dry trees are installed above the water’s surface on the deck of a platform or facility and are attached to the well below the water.
- Wet trees, on the other hand, are installed on the seabed and encased in a solid steel box to protect the valves and gauges from the elements.
- The subsea wet tree is then connected via electronic or hydraulic settings that can be manipulated from the surface or via ROVs.
- Additionally, wells may have production flowing from multiple reservoir levels. These wells require multiple completions, which keep the production separate.
- Double-wing trees are installed on multiple reservoir levels.
- completions have evolved to incorporate downhole sensors that measure flow properties, such as rate, pressure and gas-to-oil ratio. Known as intelligent wells or smart wells, these completions help to achieve optimum production rates.
Categories: Oil & Gas Notes