8/28/2020 0 Comments Casing String Design
In order to precisely place the cement slurry at a required interval on the outside of the casing, a plug is pumped with a displacement fluid behind the cement slurry column, which bumps in the casing shoe and prevents further flow of fluid through the shoe.Casing that is cemented in place aids the drilling process in several ways.Design In the planning stages of a well a drilling engineer, usually with input from geologists and others, will pick strategic depths at which the hole will need to be cased in order for drilling to reach the desired total depth.
![]() With the casing set depths determined, hole sizes and casing sizes must follow. The hole drilled for each casing string must be large enough to easily fit the casing inside it, allowing room for cement between the outside of the casing and the hole. Also, the inside diameter of the first casing string must be large enough to fit the second bit that will continue drilling. Thus, each casing string will have a subsequently smaller diameter. The inside diameter of the final casing string (or penultimate one in some instances of a liner completion) must accommodate the production tubing and associated hardware such as packers, gas lift mandrels and subsurface safety valves. Casing design for each size is done by calculating the worst conditions that may be faced during drilling and production. Mechanical properties of designed pipes such as collapse resistance, burst pressure, and axial tensile strength must be sufficient for the worst conditions. Casing strings are supported by casing hangers that are set in the wellhead, which later will be topped with the Christmas tree. The wellhead usually is installed on top of the first casing string after it has been cemented in place. Intervals Typically, a well contains multiple intervals of casing successively placed within the previous casing run. The following casing intervals are typically used in an oil or gas well. The purpose of surface casing is to isolate freshwater zones so that they are not contaminated during drilling and completion. Surface casing is the most strictly regulated due to these environmental concerns, which can include regulation of casing depth and cement quality. Intermediate casing may be necessary on longer drilling intervals where necessary drilling mud weight to prevent blowouts may cause a hydrostatic pressure that can fracture shallower or deeper formations. Casing placement is selected so that the hydrostatic pressure of the drilling fluid remains between In order to reduce cost, a liner may be used which extends just above the shoe (bottom) of the previous casing interval and hung off downhole rather than at the surface. It may typically be 7, although many liners match the diameter of the production tubing. Few wells actually produce through casing, since producing fluids can corrode steel or form deposits such as asphaltenes or paraffin waxes and the larger diameter can make flow unstable. Production tubing is therefore installed inside the last casing string and the tubing annulus is usually sealed at the bottom of the tubing by a packer. Tubing is easier to remove for maintenance, replacement, or for various types of workover operations. It is significantly lighter than casing and does not require a drilling rig to run in and out of hole; smaller service rigs are used for this purpose. Cementing Cementing is performed by circulating a cement slurry through the inside of the casing and out into the annulus through the casing shoe at the bottom of the casing string.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |