Method for Determination of Addition Amount of Cementing in Eccentric Annulus

Abstract

The invention relates to an eccentric annular cementing adding amount determining method. The eccentric annular cementing adding amount determining method comprises the steps that firstly, casing pipe eccentric degrees of all points are calculated, and the average casing pipe eccentric degree of a whole well is determined; secondly, the volume of an annular sealing section is calculated; thirdly, a finite element physical model with the length of 100 m is established and subjected to mesh partition, and replacement fluid performance and replacement displacement are input to carry out eccentric annular cementing two-phase fluid replacement numerical value simulation; fourthly, the position of drilling fluid at the rear edge of a replacement interface in the numerical value simulation process is tracked in real time, the position of the drilling fluid at the rear edge of the replacement interface and the replacement time corresponding to the position are recorded, and a function relation between the position of the drilling fluid at the rear edge of the replacement interface and the replacement time is obtained through a regression fitting method; fifthly, the replacement time needed for the drilling fluid at the rear edge of the replacement interface to reach the top of the sealing section and the needed cementing addition amount are calculated. The calculation formula of the cementing addition amount can be seen in the specification. By means of the eccentric annular cementing adding amount determining method, the reasonable cementing addition amount can be determined, and randomness and blindness of the design of the cementing addition amount are avoided.

Description

technical field [0001] The invention relates to cementing displacement technology, in particular to a method for determining additional amount of cement injection in eccentric annulus. Background technique [0002] At present, about 25% of oil and gas wells in the world have annular channeling and leakage outside the pipe to varying degrees, which increases the risk of safe production of oil and gas wells and the operating cost of remedial work, and also limits the implementation of later stimulation measures. Effect. The poor sealing ability of annular cement is the main cause of annular channeling and pipe leakage in oil and gas wells. Effectively displacing drilling fluid and ensuring that the circumferential drilling fluid completely returns to the sealing section is the key to obtaining good annular sealing. The key and prerequisite of isolation ability. [0003] During the cementing displacement process, due to the combined effects of casing eccentricity, well inclin...

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Problems solved by technology

[0005] 1) There is no unified regulation for each oilfield in the industry, only a rough value range, and this value range is quite wide, and the additional amount selected by different technicians varies greatly, which has a certain degree of blindness and randomness;

[0006] 2) The value of the additional amount of cement injection is too subjective and mainly depends on the experience of the region and technical personnel. However, the published literature does not conduct statistical analysis on the relationship between the value of the additional amount of cement injection and the sealing capacity of the annular space. There is no way to know what is the best value of additional amount of cementing for different well types in different regions, that is, there is no scientific basis for the value of additional amount determined by the experience of regions and technicians;

[0007] 3) Some regions and technicians have given the definite value of the additional amount of cement injection based on years of on-site experience, but it is based on the angle at which the cement return height meets the requirements as the determined standard, and the cement return height meeting the requirements does not necessarily mean The sealing ability of the annulus must be good, so the determination standard of the additional amount of cement injection is not reasonable, and the determination of the additional amount of cement injection can only be adapted to the specific wellbore conditions in this area, which has great limitations

[0009] 1) The displacement effect of some wells is better, and the additional amount of cement slurry required to replace the drilling fluid at the trailing edge of the interface and return to the sealing section is small. If the additional amount is designed to be large, it will cause serious waste and increase the cost of cementing operations. At the same time, the pressure of the dynamic fluid column at the bottom of the well is relatively high, and it is easy to leak the formation;

[0010] 2) The displacement effect of some wells is poor, and the additional amount of cement slurry required to replace the drilling fluid at the trailing edge of the interface and return to the sealing section is relatively large. If the additional amount is designed to be small, the drilling fluid in the sealing section will reduce the interlayer isolation Ability to even cause drilling fluid channeling

[0011] It can be seen that a reasonable additional amount of cement injection must be designed according to the actual situation of each well, and the current design of additional amount of cement injection is selected based on field experience, without theoretical guidance and determination standards, and has a certain degree of blindness and randomness. sex

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