1. Casing string strength design

Based on the introduction of advanced design methods, the strength of casing string is designed according to the different external loads borne by surface casing, technical casing and reservoir casing. The strength calculation of casing string adopts the biaxial stress calculation program and the design method of internal pressure load. The thermal stress corrosion factor is considered in the design. The strength design standard of casing string and the computer calculation program compiled according to the "standard" are compiled.

2. Cement slurry design

The basic test parameters used in the design have been changed from static to dynamic parameters of API standard, that is, from initial setting and final setting time to cement thickening time, compressive strength and rheology of cement slurry. The application of rheology to cement injection design changes the past pure cement injection into the promotion of the use of admixtures to adjust the performance of the designed cement. Flushing fluid, isolation fluid and preflush are widely used. According to the technical principle of cementing pressure balance, that is, during cementing, the static liquid column pressure of cement slurry shall be greater than the formation pore pressure, and the dynamic liquid column pressure of cement slurry shall be less than the formation fracture pressure. The density of cement slurry shall be designed to control the water loss of cement slurry less than 200ml, so as to reduce the damage to oil and gas reservoir during cementing.

Cementing process

(1) Well cementing technology in high pressure oil and gas reservoir

High pressure oil and gas wells are characterized by high formation pressure, and oil and gas channeling is easy to occur during cementing. Therefore, the research on the "weight loss" mechanism of gas channeling has been strengthened, and the graded cement injection has been studied and mastered: double setting and multi setting cement slurry injection, external packer: adding gas channeling prevention agent, gas resistance agent and fluid loss reducer; Cement injection with weighted cement slurry; A series of cementing technologies, such as wellhead annulus pressurization and the use of multi seal special casing threads.

(2) Cementing technology in deep oil and gas reservoir

In order to develop oil and gas reservoirs buried deep in the formation, the drilling holes are characterized by high temperature and high pressure, long well section and heavy casing load. In view of these characteristics, master the treatment of high temperature resistant cement and its additives, staged cement injection, liner cementing (including casing back connection technology), etc. About 40% ~ 50% of deep wells in China have adopted the methods of liner cementing and staged cement injection. The domestic tail pipe hanger and staged water injector have become a series. The graded cementing device has a series of products of various specifications, such as medium 127mm, medium 139.7mm, medium 177.8mm and medium 244.5mm, and has been trial produced into a multistage cementing device with packer and packer cementing guide shoes. It has been able to produce various specifications of external packers in China.

(3) Cementing technology for wells in low pressure and easily lost oil and gas reservoirs

This kind of well is characterized by low formation pressure coefficient, long sealing section and easy leakage. According to these characteristics, the plugging technology is mastered. Low density cement, micro bead cement, ultra low density aerated cement and foam cement cementing technology.

(4) Well cementing technology of oil and gas reservoir in rock salt layer

The rock salt layer is characterized by plastic flow and dissolution. In terms of cementing technology, master the technology of designing high-strength casing string according to the characteristics of rock salt layer and cementing with saturated brine drilling fluid (including high-density brine cement).

(5) Well cementing technology in carbonate fractured reservoir

The pressure coefficient of cracked formation varies greatly, which is easy to leak and spray, and the cementing section is long. According to its characteristics, master the cementing technologies such as dispersant, fluid loss additive, expansion agent, anti gas channeling agent, high temperature cement, liner process and graded cement injection.

4. Oil well cement

Before 1990, China's deep well cement mainly used 95 ℃ and 120 ℃ oil well cement. In 1991, China began to comprehensively promote the domestic API series oil well cement. In 1993, China's oil well cement has been transformed into oil well cement series in line with API standards. At present, China has established its own oil well cement series. In addition, new products such as low density cement, aerated cement, foam cement and impermeable cement have been developed.

5. Cement admixture

Cement admixtures have developed rapidly in recent years, with dozens of kinds in ten categories. The main products used in deep wells are weighting agent, fluid loss reducer, drag reducer, anti gas channeling agent and gas inhibitor. The weighting agents include iron ore powder, iron oxide ore powder and barite. Fluid loss additives mainly include ZOC-G80S, ZOC-G86S, ZOC-G87S, etc. Since the 1980s, in order to meet the needs of safe cementing and protection of oil and gas reservoirs such as deep wells, salt gypsum layers, small gap cementing, adjustment wells and high-pressure gas wells, China's cement slurry fluid loss additive has developed rapidly. At present, there are more than 40 kinds offluid loss additives for cement slurry in China.