Graded variable density well cementation technology

Abstract

The invention discloses a graded variable density well cementation technology and relates to the technical field of oil well production. An oil layer and an annular space below the oil layer and between a well bore and a casing are sealed by high-density cement paste, and an annular space above the oil layer and between the well bore and the casing is sealed by low-density cement paste. According to the technology, the consumption of the cement paste is lower, the additional circulating equal yield density is less increased in comparison with low density full hole section cementation, additional damages to a stratum cannot be caused, the additional circulating equal yield density can be effectively reduced, and stratum leak-off is avoided.

Description

technical field [0001] The invention relates to the technical field of oil well exploitation. Background technique [0002] Sidetracking, as an efficient and economical means of exploiting remaining oil in old areas and improving oil recovery in old areas, has been paid more and more attention by major oilfields, and has been used as a major means of increasing production. In Jiangsu Oilfield, the annual sidetracking volume is more than 40 wells, and the annual production increase is more than 40,000 tons, while the annual sidetracking volume in major oilfields across the country is several thousand wells. The length is also continuously increasing. The length of the sidetracking open hole has increased from the initial 100 meters to the current 600 meters, and some wells even reach more than 1,000 meters. The quality of sidetracking well cementing has always been the main reason affecting the service life of sidetracking wells. According to statistics, the average life of ...

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Problems solved by technology

In Jiangsu Oilfield, the annual sidetracking volume is more than 40 wells, and the annual production increase is more than 40,000 tons, while the annual sidetracking volume in major oilfields across the country is several thousand wells. The length is also continuously increasing. The length of the sidetracking open hole has increased from the initial 100 meters to the current 600 meters, and some wells even reach more than 1,000 meters. The quality of sidetracking well cementing has always been the main reason affecting the service life of sidetracking wells. According to statistics, the average life of sidetrack wells is about 3 years. How to improve the cementing quality of sidetrack wells and prolong the service life of sidetrack wells is also being explored by major oil fields. There are two main methods: (1) Expansion (2) It adopts low-density cementing technology, but these two technologies have their own shortcomings: (1) Reaming technology mainly uses special reaming tools to expand the φ118mm wellbore to about φ140mm, However, the reaming tools used in this reaming technology are immature, and limited by the original borehole (φ124mm), the normal reaming rate is about 10%, and the reaming greatly prolongs the construction period of sidetracking wells and greatly increases the construction time. cost, so this technology has not been promoted on a large scale, and major oil fields have only done relevant tests; (2) Low-density cementing technology mainly reduces the density of cement slurry to improve cementing quality. The annular gap is very small, only about 14mm, which is less than half of that of conventional wells (above 30mm in conventional wells). Reducing the density of cement slurry will obviously reduce the strength of cement slurry, although there are some high-strength additives that can improve the strength of low-density cement. The strength of the slurry, but compared with the strength of conventional cement slurry, there is still a certain decrease

[0006] (2) Low formation pressure coefficient

[0007] With the continuous deepening of oilfield development, the formation pressure coefficient continues to decrease, and the formation deficit becomes more and more serious. At present, in Jiangsu Oilfield, the normal formation pressure coefficient is about 0.3-0.5. The leakage of the cement slurry system during the well process, or the gray surface cannot return to the position of the hanger, resulting in the cementing quality not meeting the requirements

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