The casing is centered

(1) Types of centralizers. At present, there are three kinds of casing centralizers used in China: rigid centralizer, which has the largest centralizing force and diversion function, can improve the displacement efficiency, but the rigidity is also the largest; the centralizing force of double arc elastic centralizer is twice that of single arc centralizer; the centralizing force of single arc elastic centralizer is smaller than that of double arc elastic centralizer.

In domestic horizontal well cementing, rigid centralizer and double arc elastic centralizer are often used in horizontal section of horizontal well. One rigid centralizer and one elastic centralizer are added every 20 m. The centralizing force is enough to support the gravity of horizontal casing. From the theoretical calculation and practical operation results, it can ensure that the casing centering degree is greater than the requirements of horizontal well cementing cement slurry system.

In addition, there is also a swirl centralizer in China, which is based on the elastic centralizer. There are three guide vanes in the cyclone centralizer, and the best swirl diversion effect can be obtained when the guide vane angle is 35 ° to 40 ° and the opening angle is 100 ° to 115 °. The swirling centralizer makes the cement slurry form a certain swirl field in the annulus, and the higher the mainstream velocity is, the greater the intensity of the swirling field is, and the greater the circumferential velocity is formed. The test results show that the closer to the wellbore, the stronger the swirl intensity is; when the return velocity is 0.8 m / s, the effective range of the measured swirling flow field is 5 m. The actual velocity is much higher than 0.8 m / s, so the effective range of swirling flow field is also increased. In the horizontal section of well Wei 2-25, one cyclone centralizer is used in the horizontal section of well Wei 2-25, and 50 centralizers are added to each casing, and 30 centralizers are added at other positions. There is no doubt that the use of cyclone centralizer is helpful to improve the displacement efficiency.

The best methods to improve the efficiency of cement injection are movable casing and turbulent displacement. However, in the actual construction, the movable casing is difficult to implement due to various difficulties. This is especially true for highly deviated wells. In recent years, it is a new development direction to improve the displacement efficiency of cement injection by mechanical auxiliary methods such as cyclone centralizer. Based on these technologies, the rigid swirl centralizer is designed in China. On the one hand, the purpose is to support the casing under the wellbore in highly deviated well section, prevent sticking and increase the clearance of the casing, and at the same time, it can force the drilling fluid and cement flowing through the cyclone centralizer to produce swirling flow to improve the displacement efficiency. The laboratory simulation results show that the swirling centralizer can make the fluid rotate at a very low discharge rate, and the effective swirl length maintains a longer distance with the increase of displacement. After the fluid passes through the cyclone centralizer, the flow pattern changes, and the fluid rotating upward has a certain centrifugal force, which can significantly improve the displacement efficiency of the retained mud at the pipe edge and large belly hole.

(2) Centralizer placement design. Through indoor bench test and theoretical research, the value of safety factor of casing bending strength, water sealing performance and new design method of casing centralizer spacing in horizontal well casing design and strength check are studied.

The results show that: (1) when the maximum composite stress is 857 VME and the dog leg severity is 20 ° / 30 m, the suitable thread sealing grease has good water sealing performance and can meet the needs of horizontal wells. (2) The casing strength design and check can meet the technical requirements of horizontal well cementing by using the value of casing bending safety factor recommended by foreign drilling contractors. (3) The theory of longitudinal and transverse bending continuous beam with initial deflection is used to solve the problem of calculating the correct placement spacing of centralizers. Thus, API specification and sy-5334-88 are revised to treat statically indeterminate problems as statically indeterminate problems.

(3) The correct position of casing centralizer is the premise to ensure the cementing quality of deviated and horizontal wells. Based on the comprehensive analysis of the mechanical characteristics of the casing string with multiple centralizers installed, the mechanical model of a continuous beam with initial bending is adopted, and the multiple linear simultaneous equations composed of the initial bending longitudinal and transverse bending beam theory and three bending moment equations are used to theoretically solve the correct calculation method for the installation position of casing centralizers in inclined and horizontal wells.

(4) Casing centering technology. Due to the influence of well deviation angle, the gravity direction of casing, drilling fluid, cement slurry and isolation fluid in horizontal well is no longer axial but radial, which is easy to cause casing eccentricity. Once casing eccentricity displaces cement slurry, there are two difficulties: first, slurry turbulent displacement can ensure the best cementing quality, but with the increase of casing eccentricity, its critical displacement gradually increases. Second, in the eccentric annulus of casing, the flow resistance of cement slurry on the wide annular gap side is always less than that on the narrow annular gap side, resulting in the cement slurry flow velocity at the wide annular gap edge is always less than that at the narrow annular gap edge, resulting in cement slurry channeling.