RU2239058C1 - Method for localizing sources of non-natural pollution of water-bearing horizons - Google Patents

Abstract

FIELD: oil extractive industry.

SUBSTANCE: method includes complex use of measuring of natural electrical potentials in well-adjacent area and vibroacoustic cement bond logging of wells. By measuring natural electrical potentials presence and direction of behind-column liquid flows is determined in the well. By vibroacoustic cement bond logging well construction elements are determined and ranges of behind-column cement are localized, which are source of pollution and which are subject to correcting cementation.

EFFECT: higher efficiency.

9 dwg

Description

The invention relates to the field of environmental monitoring, in particular to the protection of the hydrogeological environment in oil-producing regions by quickly identifying hidden sources of salinization of groundwater for drinking purposes by ground-based geophysical methods.

In areas of intensive oil production (for example, in the southeast of Tataria), the facts of salinization of drinking water are noted, one of the reasons for which are downhole fluid flows caused by defects in annular cement (mainly a conductor or a technical column partially acting as it). The elimination of such sources of pollution is carried out by corrective cementing of defective intervals, which requires their accurate localization in depth.

A known method for detecting annular fluid flows and assessing the quality of annular cement, including thermometry, the method of radioactive isotopes and various modifications of acoustic logging (Krivko NN Equipment for geophysical research of wells. - M .: Nedra, l991, 384 c.).

The main disadvantage of this method is the high complexity and lack of responsiveness due to the need to decommission the well and carry out lengthy preparatory work involving teams of overhaul wells and special equipment (installation of the mast of the logging hoist, dismantling and removal of downhole equipment, etc.).

Closest to the proposed invention in technical essence is a method of vibro-acoustic cementometry (VAC). Determination of the quality of annular cement by the VAC method is based on the effect of reflecting part of the energy of an elastic wave as it passes through a sound pipe formed by the studied structural element of the well (production casing, conductor, etc.) through the interface between media with different acoustic impedances determined by adhesion in the metal system - cement (Blizeev AB, Kozlov A.V., Smerkovich E.S. et al. Acoustic method for diagnosing the quality of a cement ring behind a well conductor. RF Patent No. 2055176, IPC E 21 V 47/00 for 1996, bull. .№6). For this, a short acoustic impulse propagating along it is formed at the end of the studied column, after which secondary (reflected) signals are recorded. In this case, an increase in the amplitude of the secondary signal indicates the presence of annular cement defects, and the arrival time allows localization of the latter by depth and length (to determine the distance of the boundaries of defects from the wellhead by the known speed of passage of acoustic vibrations in the metal of the column).

The disadvantage of the VAC method is that it does not allow one to judge the presence or absence of annular flows, since even with a very low overall quality of cementing, such as a conductor, there may be areas of cohesive cement or tight adherence of clay rocks that prevent annular fluid circulation and salinization of freshwater horizons. Thus, the drawback of the VAC method is the insufficient reliability of the results obtained, which do not allow one to judge the presence or absence of annular fluid flows.

The objective of the invention is to increase the reliability of research results on the localization of sources of technogenic pollution of aquifers.

The problem is solved by a method including vibro-acoustic well cementing (VAC) using a survey of natural electrical potentials (EP) in the near-wellbore zone.

What is new is that in addition to the VAC, natural electric potentials (EP) are shot in the near-well zone. Using the EP survey, the presence and direction of annular fluid flows in the well are determined by the magnitude and sign of the potential gradient in the near-wellbore zone. Then, in the presence of flows, using the VAC, the quality of cementing of the well structural elements and the location of annular cement defects on them, responsible for the occurrence of flows, are determined. On the basis of these data, the question of the need for repair and insulation work on each of the elements is resolved and the depth intervals of their length, which are subject to corrective cementing, are localized.

The use of EP surveys to detect the presence of near-casing flows or leakage of mineralized water is based on the occurrence of an electric (filtration) potential when the latter move in a porous medium. This potential can be measured on the surface, and the magnitude and sign of the potential gradient in the borehole zone indicate the intensity and direction of fluid movement, respectively. (Shvydkin E.K., Napalkov V.N., Chernysheva M.G. et al. Identification of sources of drinking water pollution by oilfield effluents by the method of electric filtration potentials. // Issues of geology, exploration and development of oil and bitumen deposits. - Kazan, ed. - in KSU, 1997, p.171-176).

At the same time, this method without involving the VAC does not allow to determine a specific element of the well construction and to localize in depth the interval of its length, which determines the presence of casing flows and is subject to corrective cementing. In addition, the EP alone (without the VAC) does not allow to resolve the issue of the very need for repair work, because overflows can take place at a considerable depth beyond the limits of the occurrence of freshwater horizons and technical waters without causing anthropogenic pollution of the latter. Thus, the disadvantage of the method of shooting EP is the lack of reliability of the results that do not allow us to judge the need and the specific location of the corrective cementing.

Thus, the integrated application of the EP and VAC methods gives a fundamentally new technical result, making it possible to determine with high reliability both the need for repair and insulation works and the specific interval along the depth of the well structure element (mainly the conductor) to be cemented. Separate application of any of the above methods does not provide the necessary reliability of the results.

The presented figures explain the essence of the invention, where Figs. 1, 4, 7 show plans of isopotentials; figure 2, 5, 8 - graphs of the distribution of the electric field; figure 3, 6, 9 - cementograms given as an example of wells.

The method is carried out in the following sequence.

Using the EP method, natural potentials are shot in the region of the examined well. The value of the potential gradient ΔEP within the background values (up to 2 mV / m) corresponds to natural filtration processes, a further increase in this parameter indicates the presence of annular fluid flows, and the negative anomaly corresponds to the direction of the latter from top to bottom, and positive - from bottom to top. The intervals of annular flows are determined according to the results of the VAC, which is a graph in the coordinates of the depth - amplitude of the secondary signal, the latter is calibrated in the values: “X” (good), “XX” (partial) and “XXX” (poor adhesion to cement, flows are likely )

The proposed method has successfully passed field testing at 200 wells of OJSC “Udmurtneft” and allowed to localize over 20 sources of fresh water pollution.

As an example of a specific implementation of the proposed method, the results of the inspection of wells 547 (Figs. 1-3), 726 (Figs. 4-6) and 354 (Figs. 7-9) of Udmurtneft OJSC are given.

In well 547, there is a negative anomaly of the EP, indicating the presence of overflows from top to bottom (Figs. 1, 2). The cause of the overflows are defects annular cement conductor in the range of 5-145 m (figure 3).

In well 726, there are no anomalies of the transducer (Figs. 4, 5), which corresponds to the absence of flows and a good quality of conductor cementing (Fig. 6).

In well 354, a positive anomaly of the EP is noted (Fig. 7.8), indicating the presence of downward flow associated with defects in the annular cement in the interval 10-187 m (Fig. 9).

Technical and economic efficiency from the application of the proposed method is achieved by increasing the reliability of research results on the localization of sources of technogenic pollution of aquifers. The complex application of the EP and VAC methods gives a fundamentally new technical result (unattainable with the separate application of any of the above methods), making it possible to determine with high reliability both the need for repair and insulation works and the specific interval of the well structure element to be cemented. This has a positive effect on the timeliness of work to eliminate pollution sources and, as a result, on the environmental situation in oil producing regions.

Claims (1)

A method for localizing sources of technogenic pollution of aquifers, including vibro-acoustic well cementing (VAC), characterized in that, in addition to the VAC, natural electric potentials (EP) are shot in the near-well zone, while the presence and direction of annular fluid flows in the well are determined by surveying EP, and using the VAC, the structural elements of the well are determined and the annular cement intervals localized in depth, which are a source of pollution and must be corrected, are localized in depth th cementing.

Images