A prediction method for stuck coiled tubing in fracturing casing

Abstract

The present invention discloses a prediction method for stuck casings in coiled tubing fracturing, which includes obtaining geological parameters and physical property parameters of a coiled tubing drag sandblasting perforation fracturing well; dividing the fracture sections of a coiled tubing fracturing horizontal well into several orders; establishing a numerical model of induced stress in a coiled tubing drag sandblasting formation; calculating the curve of fracture-induced stress varying with spacing; calculating the curve of in-situ stress varying with order in a coiled tubing drag sandblasting perforation fracturing well according to the curve of fracture-induced stress varying with spacing and after superposition of induced stress; predicting the order of stuck casings during fracturing construction according to the curve of in-situ stress varying with order. The present invention proposes a prediction method for stuck casings in coiled tubing fracturing. Based on the geological parameters and physical property parameters of a coiled tubing drag sandblasting perforation fracturing well, it predicts the order of stuck casings in a horizontal well by establishing an induced stress field model, and solves the problem that it is impossible to deploy countermeasures in advance for stuck casings in coiled tubing drag.

Description

Technical Field

[0001] The invention relates to the technical field of continuous tubing fracturing of sandstone and igneous rock, and in particular to a method for predicting the sticking of continuous tubing fracturing casing. Background Art

[0002] Coiled tubing fracturing technology is a safe, economical and efficient oilfield production enhancement technology. It has been applied in oil and gas fields since the 1990s. It is particularly suitable for layer-by-layer fracturing operations in wells with multiple thin layers and gas layers and staged fracturing operations in horizontal wells. It has the advantages of fast fracturing string lifting and lowering, greatly shortening the operation time, etc. This process can accurately locate the fracture initiation position, and the scale of a single fracture is controllable, which is conducive to the targeted implementation of reservoir transformation measures, and is convenient for controlling bottom water in Carboniferous oil layers, accurate fracturing and sanding, and integrated fracturing transformation of geological engineering.

[0003] Although the continuous tubing fracturing process has obvious advantages in use, there are many problems with this technology and it needs to be improved. The continuous tubing has a soft property, which makes its force in the well complex and changeable. When the continuous tubing fracturing process technology is used for non-vertical small wellbore operations, the longitudinal load is large due to its low stiffness. During the downhole operation, the force that can be provided is small. According to its own characteristics, the inherent stability of the continuous tubing is low, and corrosion, bending and extrusion will occur, which will eventually affect its own properties, resulting in a shorter life and reduced pressure resistance. In addition, the continuous tubing is subject to greater temperature restrictions and can only operate in shallower areas. The operating cost of the continuous tubing is relatively high, which limits the application of the continuous tubing fracturing process technology.

[0004] There are many complex situations in coiled tubing fracturing, among which the occurrence of sand plugging is closely related to incomplete sand addition. The cost of coiled tubing fracturing in horizontal wells is high, the benefits are poor, and the risks of coiled tubing construction are prominent, such as the difficulty of unsealing the coiled tubing and getting stuck when lifting it up. At the same time, there are also problems such as lack of reference standards for determining the perforation time and unclear applicable formation conditions. Field practice and research have found that the main contradiction is the casing getting stuck. At present, there have been many studies on the methods of unblocking coiled tubing casing, but the mechanical properties of the coiled tubing involved in the coiled tubing fracturing construction process, the problem of getting stuck during the coiled tubing dragging fracturing, and the prediction of the fracturing construction sequence getting stuck have not yet been carried out.

[0005] Therefore, in order to reduce the risk factor of continuous tubing construction operations and increase the reliability of continuous tubing operations, it is urgent to clarify the problem of continuous tubing sticking and improve and enrich the supporting technology of continuous tubing fracturing with bottom seal. Summary of the invention

[0006] The purpose of the present invention is to provide a method for predicting the stuck casing of a coiled tubing fracturing pipe in view of the problems existing in the prior art.

[0007] The technical solution provided by the present invention to solve the above technical problems is: a method for predicting stuck of coiled tubing fracturing casing, comprising the following steps:

[0008] Step 1: Obtain the geological parameters and physical property parameters of the coiled tubing drag sandblasting perforation fracturing well;

[0009] Step 2: Divide the fracture sections of the coiled tubing fracturing horizontal well into several orders according to the geological parameters and physical property parameters of the coiled tubing drag sandblasting perforation fracturing well;

[0010] Step 3: Establish an induced stress numerical model for the coiled tubing drag sandblasting formation;

[0011] Step 4: Substitute the geological parameters and physical property parameters of the coiled tubing fracturing horizontal well into the induced stress numerical model to calculate the curve of fracture induced stress varying with spacing;

[0012] Step 5: According to the curve of fracture induced stress varying with spacing, and after superposition of induced stress, calculate the curve of in-situ stress of the coiled tubing drag sandblasting perforation fracturing well varying with order;

[0013] Step 6: Predict the order of stuck during fracturing construction according to the curve of in-situ stress varying with order.

[0014] A further technical solution is that the geological parameters include Young's modulus, Poisson's ratio, maximum horizontal principal stress, and minimum horizontal principal stress, and the physical property parameters include fracture section length and average jet point spacing.

[0015] A further technical solution is that the number of orders in Step 2 is fracture section / average jet point spacing, that is, the length of each order is the average jet point spacing.

[0016] A further technical solution is that the specific process of Step 3 is as follows:

[0017] Step 31: Based on the theory of elasticity, use the displacement discontinuity method to establish an induced stress field model for the coiled tubing drag sandblasting formation, and divide the hydraulic fracture grid units;

[0018] Step 32: Establish a coordinate system transformation method, and numerically solve the influence coefficients of the stress boundaries of each unit body;

[0019] Step 33: According to the stress superposition principle, gradually superpose the induced stresses generated by fractures of different orders, and then obtain the stress components at any point in the reservoir.

[0020] A further technical solution is that the influence coefficients of the stress boundaries of each unit body in Step 32 are:

[0021]

[0022] Where: a i is the half-length of the i-th element; are the influence coefficients of the stress boundary respectively; G is the shear modulus; ν is the Poisson's ratio.

[0023] A further technical solution is that the calculation formula for the stress components in step 33 is:

[0024]

[0025] Wherein,

[0026]

[0027] Where: are the stress components in the x-direction and y-direction respectively received by any point i around the hydraulic fracture; G is the shear modulus.

[0028] A further technical solution is that in step 6, the order or order interval corresponding to the in-situ stress equal to 0 in the curve of the in-situ stress varying with the order is the order or order interval where the fracturing construction gets stuck.

[0029] The present invention has the following beneficial effects: The present invention provides a method for predicting the sticking of a coiled tubing fracturing casing. Based on the geological parameters and physical property parameters of a well fractured by coiled tubing drag sandblasting perforation, the sticking order of a horizontal well is predicted by establishing an induced stress field model, solving the problem that the sticking of the coiled tubing dragging the casing cannot be deployed in advance. Description of the Drawings

[0030] Figure 1 is the hydraulic fracture unit provided by the present invention;

[0031] Figure 2 is the curve of the induced stress varying with the spacing of well A fractured by coiled tubing drag sandblasting perforation in the actual example of the present invention;

[0032] Figure 3 is the curve of the in-situ stress varying with the order of well A fractured by coiled tubing drag sandblasting perforation in the actual example of the present invention. Detailed Embodiments

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] The present invention provides a method for predicting the sticking of a coiled tubing fracturing casing, specifically including the following steps:

[0035] Step 1: Obtain the geological parameters and physical property parameters of the coiled tubing drag sandblasting perforation fracturing well;

[0036] Step 2: Divide the fracture segments of the coiled tubing fracturing horizontal well into several orders according to the geological parameters and physical property parameters of the coiled tubing drag sandblasting perforation fracturing well;

[0037] Step 3: Establish an induced stress numerical model for the coiled tubing drag sandblasting formation;

[0038] The specific process is as follows:

[0039] Step 31: a) The specific description of the simplified steps of the displacement discontinuity method is as follows:

[0040] During coiled tubing drag sandblasting perforation fracturing, the fracture usually consists of two surfaces. The mutual displacement amount generated by the two surfaces under the action of the in - fracture flowing pressure when the fracture is opened is called the displacement discontinuity amount of the fracture. The displacement discontinuity amount includes the tangential displacement discontinuity amount D x and the normal displacement discontinuity amount D y .

[0041] The relationship between the tangential displacement discontinuity amount D x and the normal displacement discontinuity amount D y and the displacement amount is as follows:

[0042]

[0043] In the formula: D x is the tangential displacement discontinuity amount on the fracture element body, m; D y is the normal displacement discontinuity amount on the fracture element body, m; u x (x,0 + ) and u x (x,0 - ) are the displacement amounts of the two surfaces of the fracture on the x - axis, m; u y (y,0 + ) and u y (y,0 - ) are the displacement amounts of the two surfaces of the fracture on the y - axis, m.

[0044] The tangential displacement discontinuity amount D x , the normal displacement discontinuity amount D y and the displacement field at any point in the formation are:

[0045]

[0046] In the formula: u x and u y represent the horizontal displacement and vertical displacement respectively, m.

[0047] The specific expression of the function f(x, y) is as follows:

[0048]

[0049] According to the theoretical formula of elasticity, the stress components at any point in the reservoir are:

[0050]

[0051] In the formula: σ xx is the normal stress in the x direction, MPa; σ yy is the normal stress in the y direction, MPa; τ xy is the shear stress, MPa; G is the shear modulus, MPa.

[0052] The calculation formula for the shear modulus is:

[0053]

[0054] In the formula: G is the shear modulus, MPa; E is the Young's modulus, MPa; ν is the Poisson's ratio, dimensionless.

[0055] b) Based on the theory of elasticity, use the displacement discontinuity method (DDM) to establish an induced stress field model for the coiled tubing dragging sandblasting formation, and divide the grid elements for simulation calculation.

[0056] Regarding the reservoir as a homogeneous elastic porous medium that does not undergo physical and chemical reactions with the fluid, without considering the stress changes caused by thermal stress and perforation, and considering the induced stress generated by the fracture opening, use the displacement discontinuity theory method to divide the hydraulic fracture grid elements (as Figure 1 shown).

[0057] In the local coordinate system (s, n), the displacement discontinuity of element j is denoted as and Its expression is as follows:

[0058]

[0059] In the formula: are the tangential stresses of element j in the negative and positive sides of the fracture respectively. When the negative side of the fracture moves to the right relative to the positive side is positive, and when the positive and negative sides of the fracture move relative to each other is positive.

[0060] The shear stress and normal stress at the midpoint of element i can be calculated through the displacement discontinuity of element j in Equation (1) as follows:

[0061]

[0062] In the formula: is the influence coefficient of the stress boundary.

[0063] The curved boundary is divided into n straight-line elements. The induced stresses generated by each element are superimposed to obtain the induced stress at a certain point in the formation. The known boundary conditions for any element i are:

[0064]

[0065] Substitute the boundary conditions of any element i into the calculation formulas of the shear stress and normal stress of element i to obtain the basic equations for solving this problem:

[0066]

[0067] Step 32: Since the establishment of the induced stress model requires grid division of the discrete fractures, the local coordinate system of element j needs to be transformed. After the transformation, the stress component expressions corresponding to any point i for the unit tangential constant displacement discontinuity value on element j and the stress component expressions corresponding to any point i for the unit normal constant displacement discontinuity value on element j in the total coordinate system are respectively:

[0068]

[0069] Where:

[0070]

[0071] During the transformation process, the local coordinate system (s, n) is transformed into the total coordinate system (x, y) to obtain the displacement and stress component expressions corresponding to any point i for the unit tangential constant displacement discontinuity value on element j in the total coordinate system. By transforming equations (10) and (11) from the total coordinate system (x, y) to the local coordinate system (s, n) of element i, the expression of the stress boundary influence coefficient can be obtained:

[0072]

[0073] Where: γ = β i -β j .

[0074] The stress boundary influence coefficients of each element are obtained through numerical solution as follows:

[0075]

[0076] In the formula: a i is the half-length of element i.

[0077] Step 33. According to the superposition principle, for the fractures formed by coiled tubing drag sandblasting perforation fracturing, with the horizontal wellbore axis along the x-axis direction and the fractures initiating perpendicular to the x-axis, the stress components in the x-direction and y-direction acting on any point i around the hydraulic fracture are as follows:

[0078]

[0079] Where:

[0080]

[0081] Step 4. Substitute the geological parameters and physical property parameters of the coiled tubing fracturing horizontal well into the induced stress numerical model to calculate the curve of fracture induced stress varying with the spacing.

[0082] Step 5. According to the curve of fracture induced stress varying with the spacing, and after the superposition of induced stresses, calculate the curve of in-situ stress of the coiled tubing drag sandblasting perforation fracturing well varying with the stage sequence.

[0083] Step 6. Predict the stage sequence or stage sequence interval where the fracturing operation gets stuck according to the curve of in-situ stress varying with the stage sequence.

[0084] Embodiment

[0085] 1. Obtain the geological parameters and physical property parameters of the coiled tubing drag sandblasting perforation fracturing well A (as shown in Table 1).

[0086] Table 1

[0087]

[0088]

[0089] 2. Divide the fracture section into 20 stage sequences according to the fracture section length and the average jet point spacing, and the spacing of each stage sequence is 33.74 m.

[0090] 3. Substitute the geological parameters and physical property parameters of the coiled tubing fracturing horizontal well into the induced stress numerical model, and derive the curve of fracture induced stress varying with the spacing during the coiled tubing drag sandblasting perforation fracturing process, as Figure 2 shown;

[0091] 4. There is a large induced stress near the reservoir hydraulic fracture, and the induced stress component perpendicular to the wall surface is relatively large, which is likely to cause casing deformation. After the superposition calculation of induced stresses, derive the curve of in-situ stress of the coiled tubing drag sandblasting perforation fracturing well varying with the stage sequence, as Figure 3 shown. The superposition of the induced stress generated during the first stage of the coiled tubing drag sandblasting perforation fracturing causes a change in the initial formation stress. At the same time, as the fracturing progresses, the superposition of induced stresses has an increasing influence on the formation stress, resulting in the reversal of in-situ stress and thus causing the casing to deform and get stuck.

[0092] 5. Find the sequence number at which the in-situ stress reverses according to the in-situ stress variation curve with the sequence number, and predict that the stuck pipe sequence number is between the 18th and 19th levels.

[0093] In the embodiment, under the initial formation stress condition, the superposition of the induced stress generated during the first-stage coiled tubing drag sandblasting perforation fracturing causes the initial formation stress to change. At the same time, as the fracturing progresses, the influence of the superposition of the induced stress on the formation stress gradually increases, resulting in the reversal of the in-situ stress, thereby causing the casing to deform and get stuck.

[0094] Under the geological conditions of Well A, with the increase of the sequence number, the in-situ stress difference after the superposition of the induced stress first decreases sharply and then decreases slowly. At the same time, at the 18th - 19th levels, the stress field reverses, which is the same as the actual stuck pipe sequence number.

[0095] As mentioned above, it is not any form of limitation to the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments with equivalent changes by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A prediction method for stuck coiled tubing fracturing casing, characterized in that, It includes the following steps: Step 1: Obtain the geological parameters and physical property parameters of the coiled tubing drag sandblasting perforation fracturing well; Step 2: Divide the fracture sections of the coiled tubing fracturing horizontal well into several orders according to the geological parameters and physical property parameters of the coiled tubing drag sandblasting perforation fracturing well; The number of the orders is the fracture section / average jet point spacing, that is, the length of each order is the average jet point spacing; Step 3: Establish an induced stress numerical model of the coiled tubing drag sandblasting formation; Step 4: Substitute the geological parameters and physical property parameters of the coiled tubing fracturing horizontal well into the induced stress numerical model to calculate the curve of fracture induced stress varying with spacing; Step 5: According to the curve of fracture induced stress varying with spacing, and after superimposing the induced stresses, calculate the curve of in-situ stress of the coiled tubing drag sandblasting perforation fracturing well varying with order; Step 6: Predict the order of getting stuck during the fracturing construction according to the curve of in-situ stress varying with order; Among them, determine the order or order interval corresponding to the in-situ stress equal to 0 in the curve of in-situ stress varying with order as the order or order interval of getting stuck during the fracturing construction.

2. The continuous coiled tubing fracturing casing sticking prediction method according to claim 1, characterized in that The geological parameters include Young's modulus, Poisson's ratio, maximum horizontal principal stress, and minimum horizontal principal stress, and the physical property parameters include fracture section length and average jet point spacing.

3. A method for predicting stuck of coiled tubing fracturing casing according to claim 1, characterized in that, The specific process of Step 3 is as follows: Step 31: Based on the theory of elasticity, use the displacement discontinuity method to establish an induced stress field model of the coiled tubing drag sandblasting formation, and divide the hydraulic fracture grid units; Step 32: Establish a coordinate transformation method to numerically solve the stress boundary influence coefficient of each unit body; During the transformation process, transform the local coordinate system (s, n) to the global coordinate system (x, y) to obtain the expressions of the displacement and stress components of any point i corresponding to the unit tangential constant displacement discontinuity value on unit j in the global coordinate system, and then transform the displacement and stress component expressions to the local coordinate system (s, n) of unit i to obtain the expression of the stress boundary influence coefficient; Step 33: According to the stress superposition principle, gradually superimpose the induced stresses generated by fractures of different orders, and then obtain the stress components at any point in the reservoir.

4. A method for predicting stuck of coiled tubing fracturing casing according to claim 3, characterized in that, The stress boundary influence coefficient of each unit body in Step 32 is: Where: a i is the half length of the i element; are the influence coefficients of the stress boundary respectively; G is the shear modulus; ν is the Poisson's ratio.

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