SU1677268A1 - Method for preventing casing collapse with reverse rock frosting - Google Patents

Abstract

The invention relates to the oil and gas industry. The goal is to increase the reliability of the method. Excess fluid in the interval of cavities is bypassed by installing tubes in it to form a channel connecting the cavities in the thickness of the frozen rocks with the surface. The inner surface of the tube is periodically coated with grease. The invention makes it possible to prevent the casing from sinking in the well during freezing of the rocks due to obtaining a self-regulating process of removing excess fluid without the cost of additional energy of maintaining the channel in a free state. 1 il.

Description

The invention relates to the oil and gas industry, is intended to prevent the columns of idle wells from collapsing, and can be used in construction to reduce frost heave forces on the foundations of buildings and structures, as well as to relieve pressure during accumulation of migratory gas around wells and under pile foundations of structures in the area tectonic disturbances in the territory with perennially-evil rocks.

The purpose of the invention is to increase the reliability of the method.

The drawing shows a diagram of the equipment for implementing the method.

The perforated tube 1 is placed in the well bore 2 near casing 3 with overlapping low-temperature frozen strata 4, where dangerous values of pressure develop during freezing of the cavities 5. The caverns 5 communicate with the high-temperature frozen layer 6 where the cavity 7 is located. The perforations 8 in the tube 1 are made at intervals freezing in the last place. The well has a freezing front 9 and a thawing front 10. The arrows in the figure show the direction of movement of the ice plugs 11 through the tube 1 when the pressures equalize to non-hazardous values when the excess liquid is released.

The method is carried out as follows.

The thickness of the low-temperature frozen layer 4 is determined by the magnitude of the critical pressure of the see-through of the casing string or lining well. This interval represents a hazard to the column. Using cavernometrics or geological data, we determine the placement intervals of rocks unstable during thawing (cavities 5 and 7). In tube 1, holes 8 are perforated at depths of cavities 5 and 7. We lower tube 1 to depth of frozen stratum 4 beside casing special well

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or into wellbore 2, expanded by thawing or on purpose. The inner surface of the tube is lubricated with oil products (grease) using rods or by filling them with periodic pushing them through the tube. After the thermal effect from the side of the column is stopped, when the well is stopped, the permafrost rocks 4 and 6 freeze. Freezes the liquid in the tube 1, forming ice plugs 11. In the colonial space, closed freezing volumes 9 are formed, the freezing of which is accompanied by an increase in pressure. The probability of forming a closed thawed zone is higher if the wellbore is complicated by caverns 5 and 7. But since the resistance to ice shear on the inner surface of the tube is small, at a certain pressure the ice plugs 11 lose contact with the inner wall of tube 1 and begin to move on the mouth through a layer of negative temperatures of permafrost 4 and a seasonal freezing layer. As the ice plugs move, new volumes of fluid enter the tube 1 through the perforated holes 8 and freeze as they move to the surface. Thus, continuous discharge of excess liquid in the form of ice plugs is ensured. The shear resistance of the ice along the inner wall of the tube is chosen such that the pressure developed in the volume 5 is below the pressure of the casing strings.

If there are several closed freezing volumes 5 communicating via tube 1, the removal of excess liquid in the form of ice to the surface is carried out sequentially, first from the upper cavities, then from the underlying cavities.

If the resistance forces on the movement of ice plugs to the non-day surface increase, the increasing back frost pressure moves the ice plugs to underlying closed volumes that are in a higher temperature frozen depth of 6. And as the upper part froze, the ice plugs during movement and the high temperature itself the strata begin to thaw with the formation of front 11. At the same time, the return freezing pressure will be maintained automatically at a predetermined level. And only when the upper part of the frozen layer 4 is fully frozen, the annular space in the lower part of the frozen layer 6 begins to freeze through. The final pressure value will correspond to the value of the natural temperature of the frozen layer 6.

Example. Determine the capacity of the low-temperature frozen strata by the critical pressure of the casing of the casing. According to calculations, it was 30 MPe. According to the Klaperon-Klausius equation, a pressure above the specified value occurs at a temperature of frozen rocks.

below T -30 / 13.4 -2.23 ° C. Such rock temperatures are in the depth range of up to 110 m. This range represents a hazard to the column. The cavernometry or geological data determine the placement intervals of rocks that are unstable during thawing (caverns 5 and 7), which are located at a depth of 20 to 65, from 80 to 96, and from 105 to 150 m. In tube 1, holes 8 are perforated at a depth of 45 and 88 m, Pipe 1

it is lowered to a depth of 110-115 m near casing 3. The inner surface of the tube 1 is periodically coated with lubricant.

The forces of friction sliding of ice plugs inside the tube are estimated by the forces of resistance to the shear of ice over the freezing surface. The inner wall of the tube, covered with malt, reduces the resistance to ice shear to 0.01 Mpe from 4-5 MPa for a steel unprepared wall. With an inner tube diameter of 0–3 cm, with an ice shear resistance over the freezing surface T 0.01 MPa and a maximum allowable back frost pressure, for example, P 30 MPa, we obtain the length of the ice plug 4, which is able to move along the tube

40

H P D / 4T 30 3 (4-0.01) 2250 cm.

The maximum value of ice plugs between the caverns is 20.15 and 21 m in section, which is less than H 22.5 m. Tests have shown that the maximum

5, the pressure is generated by moving the ice plugs. In the future, they are continuously moving along the tube to the surface. The water entering the tube turns into ice jams which

0 do not have time to freeze with the surface. Excessive pressure develops only in the initial period to overcome the forces of freezing, and then as it freezes, ice jams do not have time to freeze with

5, the inner wall of the tube and the actual value of T decrease.

Technical appraisal advantages of the method consist in increasing the reliability of preventing the casing string from seeing in the well when the rocks re-freeze due to obtaining a self-regulating process for removing excess fluid without additional energy costs for maintaining the channel in a free state.

Claims (1)

The invention method to prevent the see casing in the well during the reverse freezing of rocks, including the bypass 0 excess fluid in the interval of cavities by installing tubes in it to form a channel connecting the cavities in the thickness of the frozen rocks with the surface, characterized in that, in order to increase the reliability of the method, the tube is perforated in the interval of cavities in the inner surface of the tube periodically cover with grease.