Leakage during the well construction period will have a great impact on the efficiency and quality of well construction, and the down hole leakage before, during and after cementing will directly affect the quality of cementing cement ring and the sealing ability of the formation.It has the following major hazards:

‒The lack of cement ring in part of the sealing section makes the length and height of the wellbore annulus seal not consistent with the prediction, resulting in incomplete annulus seal;

‒After leakage, displacement will be directly affected and displacement model plan based on shear stress of sidewall will be changed;

‒For elastic formation, leakage may occur first and then emendation may affect the cementation of the two interfaces.

Zoranoc has a complete set of leak prevention and plugging cementing technology from theory to application.Based on the long-term research on lost circulation well condition and disposal, optimize the theory and model of lost circulation prevention and plugging, develop a new dynamic assessment instrument with independent intellectual property rights based on the simulation of various formation lost circulation and closure principles, effectively evaluate the plugging ability of plugging materials, and the field application effect is significant.In the ultra narrow pressure window cementing, lost circulation well situation disposal has rich operation experience.

LET low density cement slurry system is mainly composed of natural floating beads, artificial hollow beads and other solid lightening materials to reduce the density of cement slurry. In low density system, there are usually reinforcement materials to improve the strength and admixture materials to improve the performance of cement slurry. Based on the technology of compact packing, the solid content of cement paste per unit volume is increased and the compactness of cement paste is enhanced; By improving the surface properties of the materials, reducing the filling water between the particles and the lubricating water on the surface, the cement slurry has good rheological properties and improves the overall performance of the cement slurry. According to the temperature and applicable well conditions, let system is divided into three series, including conventional low density, economic low density and ultra-low density.

Low density cement slurry system mainly has the following characteristics：

‒The thickening time of cement slurry can be adjusted, which is good for operation safety;

‒Low water loss of cement slurry is good for reservoir protection;

‒The free liquid of cement slurry is zero, the settlement stability is good, and the channeling of cement ring is effectively prevented;

‒Good settling stability of cement slurry;

‒Cement stone is dense with low permeability;

‒Using different functional materials to improve the performance of cement paste.

Application scope of the system

‒The low density and high strength cement slurry system can be applied to various well conditions. According to the actual demand, the cement slurry density can be applied in the range of 0.9g/cm³—1.7 g/cm³ in the temperature range of 30 ℃- 150 ℃(BHST).

‒The system has a wide range of temperature and pressure applications;

‒The density of the low density and high strength cement slurry is adjustable, which can effectively prevent circulation leakage and meet the challenge of narrow pressure window;

‒The system has a wide range of temperature and pressure applications;

‒Suitable for cementing operation of low pressure and easy to leak gas well;

‒Suitable for cementing operation of oil and gas wells in long sealing section;

‒Suitable for cementing operation of underbalanced drilling.