Generally speaking, cementing operation through casing is called cementing. Cement injection plays an important role in engineering and economy. Problems in quality will lead to: no secondary and tertiary exploitation; deviation in reserve calculation; no need to exploit fluid into the well; damage to production layer.
　　The technical content of cement injection involves the selection and determination of cement injection scheme, design and calculation of cement slurry, well preparation, use of tool accessories, selection and accounting of cement injection equipment, and design of cement injection operation program, etc. In order to obtain a reasonable design, the factors affecting cement injection must be considered, generally the following items shall be considered:　　The depth of the well, the temperature gradient of the formation, the diameter of the well, the nature of the formation, etc. the drilling fluid drilling fluid system is one of the most important factors affecting the cementing quality and the success or failure of the cementing operation. Define the type and system of drilling fluid, as well as rheological properties, so as to adjust the properties of prepositive fluid, cement slurry or drilling fluid as required; casing - casing size, wall thickness, running depth, and whether centralizer and other auxiliary tools are required; casing running treatment - running speed, midway circulation, well flushing time and displacement before cement injection; cement slurry - cement slurry design, cement quantity, mixing method, admixture and rheological property of cement slurry; mixing equipment: number of cement trucks (cement pumps), mixing type, displacement, etc. 

The cementing process is generally divided into three processes: casing running, cement injection, wellhead installation and casing pressure test.
　　The casing can be divided into the following types according to the action and the depth.

Conduit: conduit is generally the shortest casing string that is introduced first. The purpose of running pipe is to prevent the shallow sand from being polluted by drilling fluid and the shallow well section from being washed out. The well section close to the surface is usually easy to be washed out because it is a loose and unconsolidated surface soil and gravel layer. In general, the conduit can also improve the return height of circulating fluid and make it return to the mud tank.　　

Surface casing: to seal the shallow loose formation and water layer; in addition to protecting the well support technical casing and production casing, surface casing also prevents the pollution of drilling fluid, underground salt water, oil and gas to surface water.　　Technical casing: when it is necessary to drill to a deeper depth, it is usually necessary to import the technical casing to ensure the safety of the borehole. The role of technical casing is often to seal and separate the complex formation which is difficult to control with drilling fluid, so as to ensure the smooth drilling.
　　Production casing: the main purpose of drilling a well is to run production casing, which is the production string of an oil well. This casing string plays the role of isolating the reservoir from other fluids in the production layer, and separating the reservoir from other formation seals in the wellbore, and forming oil and gas channels to ensure long-term production and meet the requirements of production and stimulation measures.
　　Generally, drilling and cementing is an alternate process. The following is a brief introduction to common drilling and cementing processes.
Primary spudding and surface casing cementing

After the installation of drilling equipment is completed, the first spudding shall be carried out, the surface layer shall be drilled, the bit shall be pulled out, the surface layer casing shall be run, and the preparation before cement injection shall be done immediately after the casing is run.　　

First of all, it is necessary to pump the circulating drilling fluid. Because the clearance between the casing and the wellbore is small, the mud cake on the wellbore can be impacted by the high return speed of the drilling fluid, and the performance of the drilling fluid can be adjusted until the circulating pump pressure is stable. During this period, the preparation of cement injection shall be ready, and the mixed cement slurry shall meet the design requirements to ensure the smooth construction of cement injection.
　　Before the cement slurry is injected into the casing, a certain amount of prepositional liquid shall be pumped in. The common prepositional liquid includes isolating liquid and cleaning liquid. Isolation fluid is used to isolate drilling fluid and cement slurry to avoid mixing. The cleaning fluid can clean the annular space, wash out the mud cake on the well wall, and improve the cementing quality.　　

When the measured cement is injected, release the rubber plug and start the replacement of cement slurry. When the pump pressure suddenly increases, that is, when the rubber plug reaches the bottom of the well, the pressure suddenly increases, also known as bump pressure, stop the pump, and wait for setting according to the recommended maintenance time. After testing, all indexes of cementing quality are qualified before entering the next operation procedure. The following is a schematic diagram.