Determination method of volume expansibility and contractibility of oil well cement solidification material

Abstract

The invention provides a determination method of volume expansibility and contractibility of an oil well cement solidification material. The method comprises the steps: (1) preparing slurry of the cement solidification material, (2) removing separating influence of the slurry, (3) putting the slurry into a plastic bag or a rubber bag for vacuum seal packaging, removing air and bubbles from the bag, (4) weighing with a density balance, weighing mass of water derived by a sample by using an Archimedes principle, calculating initial volume V0, weighing and calculating the volume V[bag] of the single plastic bag or the rubber bag in a similar way, (5) putting the sample in a curing environment for curing till final setting of the slurry, (6) after the final setting of the slurry, shearing off the plastic bag or the rubber bag, taking out a cement block, (7) continuing curing the cement solidification material under a set condition for preset time, measuring the volume V2 of the sample according to the method in Step (4), and (8) evaluating the volume expansibility and contractibility of the oil well cement solidification material according to the measured V0, V2 and V[bag].The method can precisely evaluate a volume change of the oil well cement solidification material.

Description

technical field [0001] The invention relates to a method for measuring volume expansion and shrinkage of oil well cement solidified materials. Background technique [0002] At present, oil well cement solidification materials such as oil well cement and plugging agent have been widely used in oil fields. Ordinary cement will shrink in volume after hardening, and volume shrinkage is a fatal flaw in the application of oil well cement in high temperature and high pressure environments. The volume shrinkage of the cement paste can't guarantee the quality of the cement sheath, and in severe cases, micro-gap may be formed, causing formation fluid channeling. Adding expansion agent to cement is one of the effective measures to prevent volume shrinkage of oil well cement. Effectively measuring the volume change of cement is one of the basic tasks to study the performance of expansion agent and the volume stability of oil well cement. [0003] In the existing national standard GB-...

AI Technical Summary

Problems solved by technology

This method has the following disadvantages: ①The cement sample and the screw micrometer move during the measurement process, and the stiffness of the screw micrometer and the sample changes during the movement, which affects the accuracy; ②This technology requires maintenance for 24±2h (after final setting) the length of demoulding is the initial length L 0 , the expansion or shrinkage of cement is measured after demoulding, only the length change of cement stone after final setting can be measured, and the volume change of cement slurry to the stage before final setting cannot be measured; oil well cement and plugging agent are at the beginning of slurry mixing Shrinkage or expansion occurs immediately after mixing, so the ideal test method is to measure the volume change of cement immediately after the slurry is mixed. It is obviously inconsistent with the real situation of the volume change of cement slurry to start measuring the volume change of cement after the final setting. There is a problem of unclear concept; ③The measurement is the length change, that is, the linear expansion rate rather than the volume change, and the volume change rate is the cube of the length change rate, so the measured length change rate is not as accurate as the volume change rate

However, this method also has the following disadvantages: the contact between the cement slurry and the tough container will be unstable due to the bleeding or air mixing on the surface of the cement slurry, so the measured data is too large, and a substitution error is also generated.

This method has the following problems: 1. The initial volume of cement is selected as the volume of the mold (5.08*5.08*5.08=131.096mL), although the mold of cement is a standard product, the volume of the mold will be affected in mold processing and use At the same time, the filling degree of the cement slurry can not be guaranteed to be exactly the same every time, so it is very unscientific to choose the initial volume as the mold volume of 131.096mL

②Put the cement stone into the beaker, and then use the container to catch the overflowing water in the beaker. This method has a very large error and is not operable.

The error caused by this may be as high as ±0.2mL, while the expansion rate of cement stone is generally about 0.3%, the error has reached 0.2 / 131=0.15%, the error is very large, this method is not advisable

[0008] To sum up, the current evaluation methods for the volume expansion of oil well cement and plugging agents at home and abroad have the following problems: ① most methods cannot measure the volume change of cement before final setting; ② the volumetric method can measure the volume change of cement before final setting, However, the influence of air bubbles cannot be eliminated, and at the same time, only the volume shrinkage of cement can be measured, and the expansion of oil well cement mixed with expansion agent cannot be measured; ③The drainage method measures the volume of cement stone by measuring the volume of water discharged from the cement stone, which will cause The splashing and adhesion of water causes large errors, the operation is cumbersome, and the operator has high requirements. At the same time, the volume change of cement can only be measured after the final setting, and the volume change before the final setting cannot be measured; ④ The measured expansion rate is linear expansion rate, and cannot simulate the volume change of oil well cement under high temperature and high pressure

However, a problem neglected by the method of this document is that during the hydration process of solidified materials such as cement, expansion agents will be added according to actual needs

However, no relevant technical reports have been found in the prior art

Images