RU2171888C2 - Method of monitoring of annular sealing - Google Patents

Abstract

FIELD: construction and operation of oil and gas wells, particularly, monitoring of sealing of annular space in development, exploratory, observation and other wells. SUBSTANCE: method is based on gamma-ray logging with use of radioisotopes in form of long-lived gaseous chemically inert radioactive isotope with monochromatic gamma radiation. This radioisotope is introduced directly into grouting mortar. Moment of starting of annular-space overflow is determined by comparison of reference gamma logging values with background gamma logging values after formation of cement stone. Radioisotope may be used in form of inert gas krypton-85. Problem of method consists in detection of moment of beginning of cement stone failure. EFFECT: higher efficiency of method. 2 cl, 1 ex

Description

 The invention relates to the construction and operation of oil and gas wells, in particular to monitoring the state of tightness of the annulus in production, exploration, observation and other purposes wells.

 It is known that annulus flows can occur in cased-hole wells due to a violation of the annulus tightness both during drilling, as a result of shock (mechanical) effects of the drilling tool on the casing, and during long-term operation of the wells, due to chemical physical influences and other reasons (Guidelines for the application of field-geophysical methods for monitoring the development of oil fields. - M .: Nedra, 1978. - 256 p.).

 The resulting channels in the cement stone contribute to the filtration of fluids from one formation to another. The complexity of their detection lies in the fact that some of them are hidden, and the lack of communication with the day surface does not mean anything about the absence of such flows. Moreover, even if there is pressure at the wellhead, it is difficult to determine its source of occurrence in the conditions of water, oil and gas saturated formations.

 It is most difficult to detect hidden flows, since traditional methods of researching wells using electric, acoustic, thermometric, and radiometric logs are for the most part insensitive to the methods of annular fluid filtration. For this reason, the results of the interpretation are mixed.

 The method of radioactive indicators is used to determine the annular circulation by injecting a labeled solution through the leakage of the column, if any, or through the perforation interval, after measuring the natural gamma activity along the wellbore. Then, gamma activity is measured after the indicator fluid is pushed into the annulus and serial bursts are displaced to the permeable formation interval or to the wellhead. By changing the values of gamma activity, the absorption sites of differently active carriers and the filtration paths are determined.

 A known method for determining the quality of cementing a well, which consists in conducting gamma-ray logging using radioisotopes located behind the casing (RF Patent N 2011813, IPC E 21 V 47/00. A method for determining intercolumn and interstratal flows in a well and a device for its implementation).

 However, this method does not in all cases make it possible to determine the presence of cracks and voids in a cement stone, but only when they form in the area of the location of a point radioactive source. In this case, the casing flow in most cases can go around the location of a point radioisotope source.

 Closest to the proposed method is a method for determining the quality of cementing wells (Pat. RF N 2054537, IPC 6 E 21 B 47/00. A method for determining the quality of cementing wells). In the known method for monitoring the tightness of the annular space, cement slurry pipes with gaseous chemically inert radioisotopes of the radon type are injected over the casing, gamma-ray logging is carried out after the formation of cement stone and gamma-ray logging after predetermined time periods, according to the results of comparing the gamma-ray logging and Background gamma-ray logging determines the beginning of annular flow. This method, with all its advantages, does not allow revealing cracks and voids in the initial stage of their formation. Since a radon-generating radioactive substance is placed in a capsule, which occupies a fixed position in the cement ring, migration of radon accumulated in the capsule can be detected only if the cement ring is substantially destroyed and the network of cracks passes in the immediate vicinity of the capsule. Indeed, the diffusion of radon in the cement ring is very slight. According to the literature (Novikov G.F. et al. Radioactive reconnaissance methods. - M .: Nedra, 1965), over the entire observation period (20-50 years), radon is distributed no more than 1 cm around the capsule. Therefore, with a high degree of probability, the overflow will be detected after it is detected by other methods - thermometry, noise metering, etc.

 The aim of the invention is to determine the quality of the cementing of the well, monitoring the state of solidity and tightness of the cement stone in time to detect the beginning of the process of its destruction.

 The method is based on gamma-ray logging using radioisotopes. In order to monitor the tightness of the annular space, a long-lived gas-forming chemically inert radioactive isotope with a relatively long half-life and monochromatic gamma radiation, which is introduced directly into the grouting mortar, is used. Using the proposed method will allow to detect behind-the-casing flow at an early stage of its appearance, to control its elimination, which will prevent environmental pollution. The tightness of the annulus can be monitored for a long time (up to 50 years) due to the long half-life of the isotope. The method does not require downloading a new portion of the indicator each time before taking measurements.

 To achieve the goal in the method for monitoring the tightness of the annulus, which consists in gamma-ray logging using radioisotopes located behind the casing, the tightness of the annular space is assessed using a gaseous long-lived isotope having monochromatic gamma radiation.

 The proposed method provides the necessary information about the beginning of the destruction of cement stone behind the column or its contact with the pipe string or the wall of the well, which makes it possible to take preventive measures before the annular flow.

 The gaseous substance is first dissolved in the carrier fluid (water, the liquid component of the cement slurry, etc.), and then introduced into the cement slurry when it is pumped into the well to a depth determined by calculation.

 After injecting the cement slurry behind the casing and the formation of cement stone, an initial "background" measurement of gamma activity is carried out.

 Then, after a specified period of time, control measurements are carried out to monitor the tightness of the annulus.

 The choice of the activity of a gaseous substance in each “mark” is made taking into account the life span of the well, the length of the “mark”, the sensitivity of the device, the absorption coefficient of gamma radiation on the way from the source to the receiver, but without exceeding the radiation safety standards NRB-76/87 and basic sanitary OSP-72/87 rules. All work at the well is also carried out taking into account the specified standards.

Example
Krypton-85 is used as a gaseous radioactive substance. A shipping container with a capacity of about 2 l is filled with a carrier fluid (water, grouting fluid, cement slurry, etc.). The estimated amount of krypton from the ampoule is transferred to the container using a special installation. The container is delivered to the well. Prior to krypton injection, natural radioactivity is measured. In the cementing process, after squeezing the estimated volume of the cement slurry, a solution of krypton in the liquid is introduced from the container into the suction hole of the cementing unit under a pressure of 0.5-0.7 MPa. The input speed is selected depending on the required length of the "mark" and the feed rate of the cement slurry. After cementing the casing and hardening, gamma-ray measurements are carried out.

 After a certain time, gamma-ray measurements are repeated with the same device and at the locations of the radioactive “tags”. A comparison of the obtained diagrams with the “background” one allows one to determine, by changes in gamma activity, the beginning of fluid movement in the annular space, even due to convective flows. By measuring with a gamma spectrometer over time, it can be determined whether the overflow is near the column or near the borehole wall.

Claims (2)

 1. A method for monitoring the tightness of the annulus, including the injection of cement slurry pipes with gaseous chemically inert radioisotopes behind the casing, conducting gamma-ray logging after the formation of cement stone and gamma-ray logging after predetermined time periods, determining the moment when the annular flow begins based on the comparison of control gamma -well logs, characterized in that a long-lived gaseous chemically inert radioisotope with monochromatic is used as a radioisotope cally gamma radiation, which lacks short-lived decay products, and injected it directly into the cement slurry.  2. The method according to claim 1, characterized in that the inert gas is krypton-85, the half-life of which is 10.71 years, having monochromatic gamma radiation with an energy of 0.5 MeV, in the absence of short-lived decay products.