SU1710701A1 - Method for location of casing collapse zone - Google Patents

Abstract

The invention relates to the gas and oil industry and is intended to determine the extent to which the casing is seeable in the intervals of the bed of the gas-oil-bearing formations overlying layers. The purpose of the invention is to increase the efficiency and accuracy of determining the degree of see casing strings. To do this, by exploration wells, one of the geophysical methods, the acoustic emission method, v ^, measures the intensity of the overburden gas-bearing horizons, which can have a crushing effect on the casing, and interpolate the measured stress values to find the equilibrium axis on the geological structure loads. The change in the gas-bearing horizon thickness is calculated due to the drop in reservoir pressure in the reservoir during its development, and the amount of movement of the crushing layer relative to the Lee casing is calculated, and the possibility of emergency see columns is judged by the value of А LI. equal to 1/2 or more of the borehole diameter. 1 tabl. 4 ill.SPs

Description

The invention relates to the gas and oil industry and is intended to determine the degree of casing of the well casing in the intervals of the overlying gas and oil-bearing formations (for example, halite, dolomite, anhydrite, etc.) in order to timely take preventive measures of technological measures and ensure trouble-free operation. wells in the process of field development.

Known methods for predicting the rate of narrowing of the wellbore when

plastic deformation of rocks based on the dependence of the flow rate of elastic-viscous media on the difference in rock pressure and the pressure of the mud column. intervals of their occurrence at the opening of the mountain range.

This technique allows characterizing the state of some rocks during the period of their passage by the drilling tool (open borehole) and cannot be effectively used to determine the dynamic characteristics of the crushing formation as an element of the geological structure of the field

its operation, i.e. when casing strings are lowered and cemented into the well.

Closest to the invention is a method for preventing the casing from being seeded in the zone of salt plastic deformation; that is, determining, on a given area for each well, the critical pressures for the fluidity of rocks that can undergo plastic deformation (Rt.t.) and geostatic pressures throughout the entire borehole section (Pr), etc.

In accordance with the characteristics of the physical state of the rocks (Rde; Pr 1; 1; 1), different zones are contoured on horizontal structural maps. According to the formula RK RE.T. - RK Kp, the predicted critical depression of the reservoir fluid is determined. formula

Pnr-apk

1b.e.

TTG

determine the time of trouble-free operation of the well, i.e. the period in which technical measures are necessary to prevent the casing from being seeded.

A disadvantage of the known method is the low efficiency of the prediction of the see zones and the lack of accuracy in determining the quantitative parameters of the deformation for conditions when the rocks acting on the casing walls are not in the elastic viscous state, as well as the significant costs associated with determination of many parameters for each well in the field (Rdet,

WG. RPT. RD RK, t6.3.).

The purpose of the invention is to increase the efficiency and accuracy of the method of determining the degree of smithing by setting quantitative parameters of the impact of rocks on a well over time even before the start of production drilling and reducing the cost of geological field research due to a reduction in their volume.

The goal is achieved by exploration wells using one of the geophysical methods — acoustic emission method — to measure the intensity of the gas-bearing layer of the horizon, which can have a crushing effect on the casing string and interpolate the measured values of intensity, find the location of the equilibrium axis on the geological structure dynamic loads.

Determination of the true position of the axis of equilibrium dynamic loads

the crushing layer increases the accuracy of finding the distance from this axis to the measurement points (determinations) of other quantities involved in the Further calculations, as well as the accuracy of the final result.

Experimental (for example, core material at the Karman plant) or by calculation using literature data determine steam; a compressibility meter of reservoir rocks, reservoir pressure simulator with a pressure drop in the reservoir, and calculate the magnitude of the gas-bearing horizon thickness measurement (reduction) (Y h). To determine the parameter A h by calculation, an applicable method is used to determine the degree of compaction of sedimentary rocks, developed by the staff of the Ministry of Agriculture and Agriculture. Then, the amount of movement of the crushing formation relative to the casing string at specific points of the field (ALi) is determined by the expression;

AU Vm 4- h - Vm- + h - (Ah - Ahi) f

where m is the distance from the measurement point to the equilibrium axis of dynamic loads, m;

h is the distance from the point ne () of the cross section of the crushing layer with the equilibrium axis of dynamic loads to the measuring point projected onto it, m;

Ah is the value characterizing the change in the reservoir thickness in the zone of equilibrium of dynamic loads, depending on the degree of compressibility of rocks with a change in the parameter Pr-Ppl - Pr. m,

where RG - geostatic pressure on the roof of the productive horizon,

RPD - reservoir pressure in the reservoir; And hi is the value characterizing the change in the collector capacity at the measuring point, m.

Prior to the development of a field at RG - RPL, the rocks forming the field constitute a stable system that can undergo changes only over a long geological period. However, during active gas extraction from the reservoir, the reservoir pressure decreases and this entails an increase in the geostatic pressure on the reservoir skeleton. The reservoir is compacted to decrease in its effective capacity and volume due to the occurrence of various types of rock deformations, as well as due to the release of liquid fluid from wet-saturated clay and other reservoirs that come into contact with the reservoir.

elements of the collector itself. This, in turn, entails a reduction in the surface of the roof of the gas-bearing horizon.

At the same time, the overlying gas reservoir and the collapsing casing, which is a more plastic, however, solid body, under the influence of the geostatic pressure of the overlying rocks, tends to occupy a new spatial position. This process is characterized by high energy intensity and proceeds abruptly.

As a result, the collapsing string PlasT moves in the vertical and horizontal planes with respect to the underlying and overlapping rocks, and, consequently, to the casing column passing in them, which ultimately leads to its clumping or destruction.

Determining the degree of casing strings is performed by setting the dynamic and linear parameters of the reservoir that crushes the column in relation to the wellbore for different zones of the field at the RG - RPL - RG, taking into account the characteristics of its geological structure.

Since the main productive layers of gas deposits are mainly represented by sandstones, aleurolites, and limestones, which, under the geological conditions under consideration, do not exhibit plastic deformations, and also because their compressive strength is relatively small and they capable of collapsing at relatively low loads, the decrease in reservoir capacity in the process of field development is beyond doubt.

On the other hand, determination of the character of see columns using lead seals and others in the process of overhaul of emergency wells also confirms the assumption that there are single sided lateral stresses in the intervals of plastic rocks;

FIG. 1 shows a field map; figure 2 is a schematic section of the reservoir; on fig.Z and 4 - forecast maps.

The essence of the prediction of the proposed method is as follows (Figures 1-3).

At the exploration stage, the period of establishing the main elements of the geological structure of the field is a structural map of the field (Fig. 1) along the top of the crushing bed, indicating isolines 1, depth 2, its occurrence, gas-bearing contour 3. A, B, C - measurement points,

coinciding with the wells in the field.

In the selected wells, the stress of the collapsing formation is determined by acoustic emission and its values 4 are plotted next to the vector icons 5.

The interpolation of acoustic emission data allows us to determine the equilibrium center of dynamic loads O, which in the given situation coincides with the center of the arched part of the field structure.

According to geological and geophysical surveys, the position of the crushing layer at Rpl is determined and the distances m and h are determined.

Figure 2 schematically shows a section of the reservoir from the roof of the crushing column reservoir to the GVK or gas-bearing contour with the image of its surface in a given direction (in Figure 2 three sections are shown in one plane, i.e., in the direction of OA, OB, OS) Rpl initial 1 (curves OA LA, S LB, OS Lc).

For the core material of the plastic collector, taken from the exploration wells, the compressibility parameter of these rocks is experimentally determined under the condition that Pn is reduced to the value determined by the field development project.

In case of insufficiency of core material, data from literature from experimental studies of similar rocks are used for calculations.

Then, for each of the points, the predicted value of the reduction of the thickness of the productive horizon is calculated and the position of the reservoir that sm4 the column is determined at Rpl.

In Figure 2, the position of the surface of the crushing formation at the time of completion of the reservoir development is represented by curve 2.

Line OM is an equilibrium axis of dynamic loads. The segment OM h is the distance on the equilibrium axis of the dynamic loads from its intersection point with the crushing layer to the measurement point projected onto it at Rpl initial. The segment OiO Ah is the distance on the equilibrium axis of dynamic loads between its intersection with the crushing layer at Rpl initial and Rpl. Flow, i.e. the change in the gas-bearing horizon thickness along the OM axis; The SS Ahf BB BB segments — the change in the gas-bearing horizon thickness at 8 measurement points. The AM, VM, SM t, and m segments are the distance from the measurement points to the equilibrium axis of the dynamic loads horizontally. Points AI, Bi, Ci - location of points A. B, C on curve 2. Points B, C - projections of points B, C from curve 1 to curve 2. ALA, Al-B, ALc - the distance the points move together with the reservoir, when the reservoir pressure decreases, it characterizes the linear lateral effect of the reservoir on the well casing and is respectively: OiAi - OiA; OiBi OiCi - OiC, which is determined by

expression:

L, Vm + h - Vm + h - (Ah - Ahj) / AC values of Ah) are plotted on the prediction map (Fig. 3). where the contours 1 are marked for the occurrence of the roof of the crushing layer with the indication of the depths 2, the gas-bearing contour 3, the measurement points (well) 4 with them. numbered 5, and zones 7-9 are allocated to varying degrees of action of the crushing formation on the casing.

As can be seen on the forecast map (Fig. 3), several deformation zones can be distinguished: an equilibrium zone 7 of horizontal dynamic loads in which the rocks move parallel to the wellbore and, as a rule, does not lead to lateral viewing of the casing, but with a significant amount of vertical displacement and the difference in the rates of re-formation of rocks in the productive and overburden intervals in the casing string, critical axial stresses (compressive or tensile) occur, resulting in continuous In the event of cracks, narrowing of the flow section and other complications, zone 8 minor deformations of the 1st, in which the degree of casing of the casing string, while observing the installation technology that does not require additional costs, allows the well to be operated without repair until the development is completed ; an accidental lateral deformation zone 9, which is acterized by a significant horizontal movement of the reservoir crushing the column, equal to or greater than 1/2 the diameter of the well.

In this connection, when designing the construction of wells in zones 7 and 9, it is necessary to plan, and during construction, to carry out various technologies for preventive measures.

The accuracy of predicting the see-through of the casing at some difficult-to-build fields requires corrective measures in determining the direction / movement of the crushing formation after

interaction analysis; tectonic elements constituting their structure.

An example of performing a prediction method.

According to the exploratory drilling data, a schematic forecast map of the Efremovsky gas condensate field (figure 4) is constructed, which shows the isolines 1 of the depth of the roof of the productive area 2, the location of the exploration wells 3 with numbers 4, contour 5 of gas content, discontinuous violations 6, contour 7 of the salt rod , the equilibrium center of dynamic loads of the crushing layer 8, the vector icons of the intensity of the crushing layer 9 and their numerical values 10

According to the geological field materials, the parameters for calculating

AL reservoir in relation to the casing of exploration wells 1-3 and summarized in

the table.

Substituting the table data in the formula AL Vm -Ь h - - h - (Ah - Ahi) f

determine AL for each well

А L2 0.29 m, А LI 0.27 m, А 0.069 m According to the calculations, we define zone 11 of emergency situations and plot it on the forecast map.

The fact that wells 12 are located with smooded casing strings in the emergency zone 11 indicated on the map confirms the ability to predict the process according to our proposed method.

The proposed method as compared with the known one has several advantages. The main effect is achieved by the ability to predict quantitative parameters and the nature of the deformation over a small

the number of exploration wells, which makes it possible to plan and carry out timely measures to prevent the casing from being smothered directly during the construction of production wells. Economic efficiency is also achieved by a significant reduction in the volume of geological field research, experimental definitions and theoretical calculations.

Economic efficiency is calculated for Krestischensky GCM on the state of the well stock as of January 1, 1986, i.e. for the period when casing strings are in the intervals of occurrence of salt formations,

overlapping gas-bearing horizons should be considered an established fact.

The basis for calculating the costs of forecasting by a known method:

3 (Ci + C2) n-N,

where Ci is the cost of no-coring work for one operation, consisting of the additional time spent on the launch-lifting operations and is determined on the basis of

g 1min b ClM3Kc

12 ,

where Syin is the cost of core sampling from a depth of 500 m;

CiManc is the cost of coring from a maximum depth of 4000 m.

According to the prices and estimates

Ci 278.16 rub.

C2 - COST of work on the preparation of a sample of the rock and the experimental determination of the physical parameters is assumed to be equal to the salary of a junior research worker for an 8-hour working day, i.e.

150: 22-6,7 rub.

n is the minimum required number of core sampling, taken to be 30;

N is the minimum required number of wells, due to the geological structure of the field, assumed to be 60.

Substituting the values in the formula, we determine the costs by a known method:

3 512.75 thousand rubles.

The costs of the proposed method are:

3- {Ci + C2) - nV- N

where Ci is the cost of core sampling for one operation, consisting of additional costs for the launching of the operation, taken in the middle of the productive interval (3500 m) according to the rates of 428.58 rubles;

Ca - the cost of work on sample preparation and experimental determination of the parameters of Parameters is 6.7 rubles;

n - the minimum required number of core sampling operations from plasto collectors is 6;

N - the minimum required number of exploration wells in the area is 15.

Substituting the values in the formula, we determine the cost of forecasting by the proposed method:

3 39.17 thousand rubles.

The economic effect is the difference in cost of the known and proposed method:

E 3 - 3 473,58 thousand rubles.

Thus, the annual economic effect only on Krestischensky GKM will amount to 473.58 thousand rubles.

The application of the proposed method in the Ukrgazgrom software will allow the economic effect to be increased several times.

Formula 3 and Br

The method of determining the emergency seepage of casing strings, including the determination of the lithologic and physical characteristics of the productive horizons, the construction of forecast maps from geological field data, characterized in that, in order to increase the efficiency and accuracy of the method, the intensity of the crushing layer is measured by acoustic emission, by interpolating the obtained data on the structure of the field, the equilibrium axis of the dynamic loads is found, the change in the thickness of the gas-bearing horizon is calculated in connection with the fall of the plate TO O-O pressure in the reservoir during its development and -compute the amount of movement of the crushing layer relative to the casing according to the following expression:.

whether m2 + h2

-V

(b-Ahijf

where m is the distance from the measurement point to the equilibrium axis of dynamic loads, m;

h is the distance from the point of intersection of the crushing layer with the equilibrium axis of dynamic loads to the measuring point designed for it, m;

Db is the magnitude of the change in reservoir capacity in the zone of equilibrium of dynamic loads depending on the compressibility of rocks with a decrease in reservoir pressure in the reservoir;

L | - the magnitude of the change in the reservoir power at the measurement point, m, and the possibility of emergency see columns is judged by a Lie value equal to 1/2 or more of the borehole diameter.

Note:

 for determining Ah, Ahi, the literature data are used and the L Vex is assumed for plastic deformation of 2%, and the volume change during elastic deformation is calculated from

Formula AV-y3 LR V, where ultrasound 1 10.

// J S

fpue. 2

Claims (1)

Claim A method for determining emergency collapse zones of casing strings, including determining the lithological and physical characteristics of productive horizons, building forecast maps from geological and field data, characterized in that, in order to increase the efficiency and accuracy of the method, the pressure of the crushing formation is measured by acoustic emission by interpolating the obtained data on the structure of the field find the axis of equilibrium of dynamic loads, calculate the change in the thickness of the gas-bearing horizon in connection with the fall of the reservoir th pressure in the reservoir during its development, and calculating the amount of movement crushes formation relative to the casing by the following expression, _____________. . '. Δ Li = m ² + h ² ~ m ² + [h - (Δ h - Δ hi)] ² where m is the distance from the measuring point to the axis of equilibrium of dynamic loads, m; ’H — distance from the point of intersection of the crushing bed with the axis of equilibrium of dynamic loads to the measuring point designed for it, m; ΔΗ is the magnitude of the change in reservoir power in the zone of equilibrium of dynamic loads depending on the compressibility of the rocks with a decrease in reservoir pressure in the reservoir; Ahi is the value of the reservoir power change at the measuring point, m, and the possibility of emergency collapse of the columns is judged by the value Δίι equal to 1/2 or more of the diameter of the well. ΙΦ wells t, m h, M Bff.m Ah, M * Ahi.M * Ah ~ Ah |, M 2 4500 450 thirty 3.6 0.7 2.9 1 2300 300 60 - 1,5 2.1 3 1500 150 120 - 2.9 0.7 Note: * To determine Ah, Ahi used and accepted literature data A Vex under plastic strain of 2%, and volume change during the elastic deformation is calculated from Eq AV "β · Δ P * V, where β = 1 xlO ^5. Compiled by V. Nikulin Editor N. Khimchuk Tehred M. Morgenthal Corrector N. Revskaya Order 318 Circulation Subscription VNIIIPI State Committee for Inventions and Discoveries under the State Committee for Science and Technology of the USSR 113035, Moscow, Zh-35. Raushskaya nab., 4/5 Production and Publishing Plant Patent, Uzhgorod. Gagarin St. 101