An optimization method for encrypting well trajectory around obstacles

Abstract

The present application relates to the technical field of oil and gas, and discloses an optimization method for a barrier-encircling trajectory of a infill well, which comprises the following steps: step 1, establishing a geometric model of a fracture risk zone; step 2, establishing a formula for the perpendicular distance from a point on a direction line to the axis of a main fracture and a formula for a collision-preventing radius; step 3, calculating the nearest point from the fracture risk zone on a starting direction line and a target direction line; step 4, optimizing the trajectory design type; step 5, setting the constraint conditions for the designed trajectory of the well to be drilled; step 6, calculating the seepage ellipsoid volume and intersection volume of the main fracture; step 7, considering the interference effect of the main fracture, calculating the daily production capacity of the block to be drilled; and step 8, calculating the development cost and income of the block to be drilled; taking the net present value as a target function, solving the optimal barrier-encircling trajectory length, and completing the optimization of the barrier-encircling trajectory of the infill well. The present application can make the optimized trajectory safely bypass the fracture risk zone and have the optimal economic benefit.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas technology, in particular to an optimization method for barrier-avoiding trajectory of infill well. BACKGROUND

[0002] After the productivity of shale gas cluster horizontal well group enters the decline period, in order to realize long-term stable production and productivity replacement, it is necessary to deploy infill wells on the basis of the original well deployment. Due to the influence of volume fracturing of the drilled well, the formation becomes more complex, resulting in increased drilling difficulty and intensified fracture interference effect. In order to realize safe and efficient deployment of infill wells, the well trajectory needs to be further designed and optimized in combination with the formation characteristics of the to-be-drilled block. At present, scholars at home and abroad mainly identify the fractures of the formation through seismic data, and design the well trajectory to avoid the fracture risk area when the fracture is drilled, according to the size and other information of the fracture. On the premise of meeting economic and technical indicators, the well trajectory is optimized, which can effectively reduce the drilling risk, shorten the design trajectory length, and thus improve the mining benefit. Therefore, it is of great significance to establish an optimization design method for barrier-avoiding trajectory of infill well.

[0003] At present, there are relatively few methods for optimizing the barrier-avoiding trajectory of infill well from the economic value angle, and more are from the technical angle to analyze the optimal trajectory design of infill well. For example, the patent with the publication number CN111980696A discloses a well trajectory optimization method, which further optimizes the well trajectory based on the minimum distance between the fracture and the well trajectory, adjusts the trajectory design parameters according to the formation characteristics, improves the drilling efficiency, shortens the trajectory length, and reduces the drilling cost and cycle. However, in the volume fracturing area of the drilled well, the interference effect of the main fracture is significant, and the well trajectory obtained by this method will not achieve the expected productivity of the to-be-drilled block. Moreover, this method tends to optimally select the existing trajectory design scheme, and relying on trial calculation will reduce the effectiveness of trajectory design. SUMMARY

[0004] The present application provides an optimization method for barrier-avoiding trajectory of infill well to solve the problems in the prior art.

[0005] The technical scheme adopted by the present application is:

[0006] An optimization method for barrier-avoiding trajectory of infill well, comprising the following steps:

[0007] Step 1: Obtain the microseismic data of the to-be-drilled block, and establish a geometric model of the fracture risk area;

[0008] Step 2: Obtain the information of the start point direction line and the target point direction line of the to-be-drilled well, and respectively establish the vertical distance formula from a point on the start point direction line and the target point direction line to the main fracture axis and the anti-collision radius formula;

[0009] Step 3: Calculate the nearest point of the start point direction line and the target point direction line to the fracture risk zone;

[0010] Step 4: According to the perpendicular distance of the nearest point obtained in step 3 and the anti-collision radius, select the trajectory design type;

[0011] Step 5: Obtain the drilling operation restriction conditions of the to-be-drilled block, and set the constraint conditions of the to-be-drilled well design trajectory;

[0012] Step 6: Obtain the shale gas development parameters of the to-be-drilled block, obtain the daily production capacity of the main fracture, and calculate the seepage ellipsoid volume and intersection volume of the main fracture;

[0013] Step 7: According to the calculation results obtained in step 6, considering the interference effect of the main fracture, the daily production capacity of the to-be-drilled block is calculated;

[0014] Step 8: Considering the economic benefit of the infill well, the development cost and income of the to-be-drilled block are calculated; taking the net present value as the objective function, the optimal trajectory length is solved, and the optimization of the infill well obstacle-avoiding trajectory is completed.

[0015] Further, the fracture risk zone geometric model construction method in step 1 is as follows:

[0016] According to the microseismic data, the fracture characteristics of the drilled well volume fracturing are obtained; the fracture characteristics include main fracture distribution information and fracture scale information;

[0017] The axis endpoint of the main fracture M The vector length of 0 is p0, the inclination angle is α 0, the azimuth angle is φ 0, and the unit direction vector is t0.

[0018] The geometric model of the fracture risk zone is a spatial ellipsoid, and the axis lengths of the ellipsoid are a 、 b 、 c .

[0019] Further, the construction method of the perpendicular distance formula of a point on the direction line to the main fracture axis and the anti-collision radius formula is as follows:

[0020] According to the to-be-drilled well bottom information, the start point direction line and the target point direction line information are obtained;

[0021] The vector length of the start point A is p A , the inclination angle of the direction line is α A , the azimuth angle is φ A , and the unit direction vector is t A ; the vector length of the target point T is p T, the inclination of the direction line is α T , the azimuth is φ T , and the unit direction vector is t T ;

[0022] Suppose drilling along the starting direction line, M is a point on the direction line with a depth of s , the vector length of M is ;

[0023] Passing through M , the perpendicular to the main fracture axis is MM A , and the foot is M A ;

[0024] The distance from a point on the starting direction line to the perpendicular to the main fracture axis is D A The calculation formula is as follows:

[0025]

[0026] In the formula: is the direction vector of straight line MM 0;

[0027] The distance from a point on the target direction line to the perpendicular to the main fracture axis is D T The calculation method is as D A The calculation method.

[0028] Calculate the length of the semi-major axis of the cross-sectional ellipse at M A ; a A and the length of the semi-minor axis b A ;

[0029] Calculate the intersection coordinates of the perpendicular MM A and the cross-sectional ellipse ( x A , y A );

[0030] The anti-collision radius of a point on the starting direction line and the fracture risk zone is d A The calculation formula is as follows:

[0031]

[0032] Similarly, the target direction line and the crack risk area d T The calculation method is as follows d A The calculation method is as follows

[0033] Further, the calculation method of the nearest point on the target direction line to the crack risk area is as follows:

[0034] If M is the nearest point on the target direction line to the crack risk area, according to the function extreme condition, we have:

[0035]

[0036] From the above equation, the equation about the well depth s is obtained, and according to the equation about the well depth s , the coordinates of the nearest point on the target direction line are obtained.

[0037] Similarly, the calculation method of the nearest point on the target direction line to the crack risk area is as follows:

[0038] Further, the selection method of the trajectory design type is as follows:

[0039] The vertical distance of the nearest point on the target direction line is calculated D Amin and the anti-collision radius d Amin The vertical distance of the nearest point on the target direction line is calculated D Tmin and the anti-collision radius d Tmin .

[0040] If D Amin is less than d Amin or D Tmin is less than d Tmin , the obstacle trajectory adopts a double circular arc trajectory model;

[0041] If D Amin is less than d Amin and D Tmin is less than d Tmin , the obstacle trajectory adopts a three circular arc trajectory model.

[0042] Further, the drilling operation restriction conditions include target accuracy, wellbore curvature, well length and anti-collision constraint;

[0043] The target accuracy of the drilling operation satisfies:

[0044]

[0045] wherein, N is the number of well sections, i is the well section number, , , are the increments of the first i well section in the X , Y , Z directions, , , are the coordinate differences of the tripping-out point A of the well to be drilled and the target point T in the X , Y , Z coordinates, δ is the allowable error value, L i is the length of the first i well section, is the rate of change of the inclination angle of the first i well section, is the rate of change of the azimuth angle of the first i well section, α is the inclination angle, φ is the azimuth angle, is the change amount of the inclination angle, is the change amount of the azimuth angle;

[0046] The borehole curvature of the circular arc section trajectory satisfies:

[0047]

[0048] wherein, is the borehole curvature limit value of the first i well section, k i is the borehole curvature of the first i well section;

[0049] The length of each well section satisfies:

[0050]

[0051] wherein, is the minimum value of the length of the first i well section, is the maximum value of the length of the first i well section, L iFor the first i The length of the well section.

[0052] The design trajectory includes anti-collision constraints, which ensure that each well section does not collide with the fracture risk zone;

[0053] Assumption M For the first i The well section depth is s One point, taking the first well section of the designed trajectory as an example, is that... M The radius P M for:

[0054]

[0055] R 1 represents the radius of curvature of the first well section, and n A Starting point A Principal normal vector;

[0056] The calculation method for the nearest point to the fracture risk zone in the first well section is the same as in step 3, and the anti-collision radius is also used. d 1min Distance from the perpendicular line D 1min The calculation method is the same as in step 2;

[0057] If there exists any i.e. i well section d imin > D imin If so, the obstacle avoidance trajectory needs to be redesigned until all well sections can safely bypass the fracture risk zone.

[0058] Furthermore, the seepage ellipsoidal volume of the main fracture A as follows:

[0059]

[0060] in, a The length of the main crack, ξ R It is the outer boundary of the ellipsoid;

[0061] Intersecting volume B The calculation method is as follows:

[0062]

[0063] in, F ( x ) is a function for calculating the overlapping volume. To be related to the main crack P The main fracture above the adjacent well. φ 0 is the azimuth of the main crack. A 1 andA P The main cracks P 1 and P The seepage ellipsoid volume.

[0064] Intersecting volumes of seepage ellipsoids B 2. Calculation method is the same B 1. Calculation method.

[0065] Furthermore, the daily production capacity of the block to be drilled... q sc The calculation method is as follows:

[0066]

[0067] in, q 1. q 2 and q P The main cracks P 1. P 2 and P Daily production capacity q ex This is the daily production capacity of the remaining main fractures within the block to be drilled. A 1. A 2 and A P The main cracks P 1. P 2 and P The volume of the seepage ellipsoid, B 1 and B 2 are the intersecting volumes of the seepage ellipsoids of adjacent main fractures.

[0068] Furthermore, the revenue CI The calculation method for cash inflow is as follows:

[0069]

[0070] in: CI ( t ) is the first t Annual cash inflow W r For the commodity rate of natural gas, P For natural gas sales price, Q ( t ) is the first block to be drilled t Annual production capacity;

[0071] Development costs CO For cash outflows, the calculation method is as follows:

[0072]

[0073] wherein: CO ( t ) is the cash outflow in the year of 2017, t C s is the drilling cost per unit length of the well to be drilled, L h is the linear segment trajectory length of the well to be drilled, L is the trajectory length of the well to be drilled around the barrier, C f is the volume fracturing cost, C Mg is the operating cost per unit gas production;

[0074] The objective function is expressed as follows:

[0075]

[0076] wherein: NPV is the net present value, n is the project evaluation period, j is the annual discount rate.

[0077] The present application has the following beneficial effects:

[0078] (1) The present application regards the fracture risk zone in which complex situations are likely to occur in the to-be-drilled block as a spatial ellipsoid, and can design the wellbore trajectory that may enter the risk zone in a targeted manner;

[0079] (2) The present application converts the influence of the infill well on the productivity of the to-be-drilled block into a seepage ellipsoid volume intersection problem, and predicts the productivity of the to-be-drilled block according to the interference effect of the main fracture;

[0080] (3) The present application proposes an optimal net present value design method for the barrier-encircling trajectory of the infill well from the perspective of combining economy and technology, thereby improving the exploitation benefit of the infill well, and making the determination of the optimal barrier-encircling trajectory length more reasonable. BRIEF DESCRIPTION OF DRAWINGS

[0081] Figure 1 is a schematic diagram of the to-be-drilled well starting point direction line, the main fracture axis and the fracture risk zone.

[0082] Figure 2 is a schematic diagram of the trajectory design type of the present application, 2-a is a double-arc cross-section trajectory design diagram, and 2-b is a three-arc cross-section trajectory design diagram.

[0083] Figure 3 is a schematic diagram of the fracture interference effect of the main fracture of the present application.

[0084] Figure 4 is a graph of the net present value of the to-be-drilled well changing with the trajectory length according to the present application. ​

[0085] Figure 5 The anti-collision risk schematic diagram for the trajectory of the well to be drilled is optimized.

[0086] Figure 6 The profile comparison diagram of the design results of different trajectory lengths of the well to be drilled is provided.

[0087] Figure 7 The interference effect comparison diagram of the main fractures of the block to be drilled is provided. P 1, P 2 and P The interference effect comparison diagram of the main fractures of the block to be drilled is provided. L =714.3m corresponding to the interference effect schematic diagram, and b is the interference effect schematic diagram corresponding to the around-obstacle trajectory length L =816.3m.

[0088] Figure 8 The cumulative productivity change rule with time of the main fractures of the block to be drilled is provided. P 1, P 2 and P The cumulative productivity change rule with time of the main fractures of the block to be drilled is provided. DETAILED DESCRIPTION

[0089] The present application will be further described below in combination with the drawings and specific embodiments.

[0090] An optimization method of an around-obstacle trajectory of a cryptic well, comprising the following steps:

[0091] Step 1: obtaining microseismic data of a block to be drilled, and establishing a geometric model of a fracture risk area;

[0092] After the microseismic data is collected, high-resolution processing is performed to obtain the fracture characteristics of the volume fracturing of the drilled well, including the main fracture distribution information and the fracture scale information, and the geometric model of the fracture risk area is established as follows:

[0093] The geometric model of the fracture risk area is a spatial ellipsoid as shown in Figure 1 The axis lengths of the ellipsoid are a , b , c The vector radius of the end point M 0 of the main fracture axis is p0, the inclination angle is α 0, the azimuth angle is φ 0, and the unit direction vector is t0.

[0094] Step 2: obtaining the information of the start point direction line and the target point direction line of the well to be drilled, and establishing the perpendicular distance formula from a point on the direction line to the main fracture axis and the anti-collision radius formula;

[0095] The vector radius of the start point A is p A , and the inclination angle of the direction line is αA , the azimuth angle is φ A , the unit directional vector is t A ; the target point T , the vector length is p T , the inclination angle of the directional line is α T , the azimuth angle is φ T , the unit directional vector is t T ;

[0096] Assuming drilling along the starting directional line, M is the point with a well depth of s on the starting directional line, the vector length of M is , wherein t A = ( , , );

[0097] As shown in Figure 1 , the perpendicular line M passing through the main fracture axis MM A , the foot point is M A ;

[0098] The distance of a point on the starting directional line to the perpendicular line of the main fracture axis D A is calculated as follows:

[0099]

[0100] In the formula: is the directional vector of straight line MM 0;

[0101] The distance of a point on the target directional line to the perpendicular line of the main fracture axis D T is calculated as follows: D A The calculation formula.

[0102] The length M 0 M A of is obtained, and the length of the semi-major axis of the cross-sectional ellipse at M A is calculated as a A and the length of the semi-minor axis is b A ;

[0103]

[0104] Calculate the perpendicular line MM A The intersection point of the cross-sectional ellipse and the local coordinate system M A -t a t b coordinates below ( x A , y A ):

[0105]

[0106] Where t a for M A The unit direction vector of the major axis of the ellipse at the cross section, t b for M A The unit direction vector of the minor axis of the ellipse at the cross section;

[0107] Collision avoidance radius of the starting direction line d A The calculation formula is as follows:

[0108]

[0109] In particular, when MM A and t a When they are perpendicular, the collision avoidance radius d A for b A ,when MM A and t b When they are perpendicular, the collision avoidance radius d A for a A ,when M A When not located within an ellipsoid, the collision avoidance radius is... d A It is 0.

[0110] The collision avoidance radius between a point on the target direction line and the crack risk zone d T The calculation formula is as follows d A Calculation formula.

[0111] Step 3: Calculate the nearest point from the starting point direction line and the target point direction line to the crack risk zone;

[0112] like MThe nearest point of the fracture risk zone on the starting direction line is the nearest point on the starting direction line to the fracture risk zone, and the function extreme condition is as follows:

[0113]

[0114] The equation about the well depth s is obtained from the above formula, and the coordinates of the nearest point on the starting direction line are obtained according to the equation about the well depth s. s

[0115] Similarly, the calculation method of the nearest point of the fracture risk zone on the target direction line is the same as the calculation method of the nearest point on the starting direction line.

[0116] Step 4: Calculate and compare the perpendicular distance of the nearest point and the anti-collision radius, and preferably select the trajectory design type;

[0117] The perpendicular distance of the nearest point on the starting direction line is calculated D Amin and the anti-collision radius d Amin The perpendicular distance of the nearest point on the target direction line is calculated D Tmin and the anti-collision radius d Tmin .

[0118] If D Amin is less than d Amin or D Tmin is less than d Tmin , the barrier trajectory adopts a double-arc trajectory model, as shown in Figure 2 -a.

[0119] If D Amin is less than d Amin and D Tmin is less than d Tmin , the barrier trajectory adopts a three-arc trajectory model, as shown in Figure 2 -b.

[0120] Step 5: Obtain the drilling operation limit conditions of the to-be-drilled block, and set the constraint conditions of the to-be-drilled well design trajectory;

[0121] The drilling operation limit conditions include target accuracy, wellbore curvature, well length and anti-collision constraints;

[0122] The target accuracy of the drilling operation satisfies:

[0123]

[0124] wherein,​N is the number of well sections, i is the well section label, , , are the first i well section in X , Y , Z directional increments, , , are the coordinates of the drilling point A and the target point T in X , Y , Z coordinate differences, δ is the allowable error value, L i is the length of the first i well section, is the rate of change of the inclination angle of the first i well section, is the rate of change of the azimuth angle of the first i well section, α is the inclination angle, φ is the azimuth angle, is the inclination angle change amount, is the azimuth angle change amount;

[0125] The borehole curvature of the circular arc section trajectory satisfies:

[0126]

[0127] wherein, is the borehole curvature limit value of the first i well section, k i is the borehole curvature of the first i well section;

[0128] The length of each well section satisfies:

[0129]

[0130] wherein, is the minimum value of the length of the first i well section, is the maximum value of the length of the first i well section, L i is the length value of the first i well section.

[0131] The anti-collision constraint of the designed trajectory is to ensure that each well section does not collide with the fracture risk area;

[0132] It is assumed thatM For the first i Well section Well depth is s A point, the first well section of the design trajectory, for example, the vector of M The radius is:

[0133]

[0134] R 1 is the radius of curvature of the first well section, n A The main normal vector of the starting point A ;

[0135] The first well section on the nearest point to the fracture risk zone calculation method with step 3, the anti-collision radius d 1min And the calculation method of the vertical distance D 1min With step 2;

[0136] If there is any i Well section d imin > D imin Then the design of the trajectory around the barrier needs to be redesigned until all well sections can safely bypass the fracture risk zone.

[0137] Step 6: Obtain the shale gas development parameters of the block to be drilled, get the daily capacity of the main fracture, calculate the seepage ellipsoid volume and intersection volume of the main fracture;

[0138] The daily capacity of the main fracture can be calculated by the commonly used Fracpro, stimplan, petrel fracturing software simulation.

[0139] The seepage ellipsoid volume of the main fracture A As follows:

[0140]

[0141] Among them:

[0142]

[0143] In the formula: a The length of the main fracture, k f The fracture permeability; μ The viscosity of natural gas; φ The porosity; The comprehensive permeability coefficient of gas reservoir; t D The main fracture production time, ξ R The outer boundary of the ellipsoid;

[0144] Intersection volume B 1The calculation method is as follows:

[0145]

[0146] Wherein, F ( x ) is a function for calculating the overlapping volume, which can be realized by Monte Carlo random point method in Matlab, is the main fracture P adjacent to the main fracture on the infill well, φ 0is the azimuth angle of the main fracture, A 1and A P are the seepage ellipsoid volumes of the main fractures P 1and P .

[0147] Seepage ellipsoid intersection volume B 2The calculation method is the same as that of B 1.

[0148] Step 7: According to the calculation results obtained in step 6, the daily production capacity of the to-be-drilled block is calculated considering the interference effect of the main fracture;

[0149] The interference effect of the main fracture is that the intersection of the seepage ellipsoid of the main fracture will cause the production capacity loss in the intersection area.

[0150] Daily production capacity of the to-be-drilled block q sc The calculation method is as follows:

[0151]

[0152] Wherein, q 1, q 2and q P are the daily production capacities of the main fractures P 1, P 2and P , q ex is the daily production capacity of the remaining main fractures in the to-be-drilled block, A 1, A 2and A P are the seepage ellipsoid volumes of the main fractures P 1, P 2and P , B 1and B 2are the intersection volumes of the seepage ellipsoids of the adjacent main fractures.

[0153] Step 8: Consider the economic benefits of the infill well, calculate the development costs and revenue of the block to be drilled; use net present value as the objective function to solve for the optimal trajectory length, and complete the optimization of the obstacle avoidance trajectory of the well to be drilled.

[0154] The economic benefit of drilling and development is the sales revenue from production and operation minus the development costs of infill wells. The sales revenue from production and operation, i.e., the cash inflow, mainly consists of natural gas sales revenue, and can be expressed as:

[0155]

[0156] in: CI ( t ( ) represents the cash inflow for the year, in ten thousand yuan. W r For the commodity rate of natural gas, P This is the selling price of natural gas, in units of 10,000 yuan / 10. 3 m 3 , Q ( t ) is the first block to be drilled t Annual production capacity, 10 3 m 3 .

[0157] The development costs for a well to be drilled include pre-production costs and production costs. Pre-production costs mainly consist of drilling and fracturing costs for infill wells, while production costs mainly consist of operating costs. This can be represented as:

[0158]

[0159] in: CO ( t ) is the first t Annual cash outflow, in ten thousand yuan. C s The drilling cost per unit length of the well to be drilled is expressed in yuan / m. L h The length of the straight section of the well trajectory to be drilled is in meters (m). L The length of the obstacle avoidance trajectory for the well to be drilled is in meters. C f Cost of volumetric fracturing, in ten thousand yuan. C Mg The operating cost per unit of gas produced, expressed in yuan / m³. 3 ;

[0160] For a double-circular-arc design trajectory, the length of the obstacle bypass section to be drilled is:

[0161]

[0162] For the three-circle arc design trajectory, the length of the obstacle bypass section to be drilled is:

[0163]

[0164] in, L 1. L 2 and L 3 represents the lengths of the first, second, and third circular arc segments, respectively, in meters (m).

[0165] Net present value (NPV) is an evaluation indicator of the economic benefits of infill well development. Considering the time value of money, the objective function of the optimization model can be expressed in terms of NPV:

[0166]

[0167] in: NPV Net present value, in ten thousand yuan. n The project evaluation period is in years. j is the annual discount rate, a decimal.

[0168] Then, a heuristic algorithm is used to solve for the optimal trajectory length.

[0169] Example

[0170] The following explanation focuses on a specific well to be drilled.

[0171] Before designing and optimizing obstacle avoidance trajectories for infill wells, it is necessary to use the design wizard to guide operators in inputting the necessary initial information, including trajectory design parameters, formation fracture parameters, shale gas development parameters, and economic benefit evaluation parameters.

[0172] Trajectory design parameters: wellbore curvature 2.0 ° / 30 m, length of each well section not less than 0, error value δ Less than 0.005. (Based on a point at a well depth of 2000m.) A The starting point for drilling, point A The coordinates are (-265 m, 176 m, 2271 m), and the well inclination angle is... α A It is 103°, azimuth angle φ A 135°; target point T The coordinates are (440 m, -529 m, 2290 m), and the well inclination angle is... α T =89°, azimuth angle φ T =135°.

[0173] Formation fracture parameters: Microseismic monitoring shows a main fracture between the initiation point and the target point. PThe fracture zone formed has a length of 80 m, a width of 30 m, and a height of 30 m, and the end points of the main fracture axis are M 0 coordinates (3 m, -92 m, 2288 m), and the inclination α 0 is 1 °, and the azimuth φ 0 is 225 °. It is planned to perforate and fracture every 150 m on the infill well, with the main fracture length of the fracture being 80 m. A

[0174] Shale gas development parameters: the horizontal well of the block to be drilled has been exploited for 2 years, the wellbore radius is 0.05 m, the fracture permeability is 30 μ m 2 , the gas viscosity is 0.025 mPa*s, the formation porosity is 0.096, the gas comprehensive compressibility is 0.12*1 / MPa, and the evaluation period of the infill well is 2 years.

[0175] Economic benefit evaluation parameters: the price of natural gas is 4.5 yuan / m 3 , the discount rate is 8%, the commercial rate of natural gas is 97%, the drilling cost per unit length of the infill well is 1100 yuan / m, the operating cost per unit gas output is 0.38 yuan / m 3 , and the fracturing cost of the infill well in the block to be drilled is 300,000 yuan.

[0176] The specific design method is as follows:

[0177] Step 1: For the above-mentioned well to be drilled, collect the seismic data of the block and perform high-resolution processing to obtain the fracture characteristics of the formation, including the main fracture distribution information and the fracture zone scale information, including the vector radius p M 0 of the end points of the main fracture axis

[0178] Establish a geometric model of the fracture risk zone, as shown in Figure 1 . Among them, the axis lengths of the ellipsoid are a =80 m, b =30 m, c =30 m.

[0179] Step 2: Obtain the information of the starting point direction line and the target point direction line of the well to be drilled, including the vector radius p A of the starting point A , the vector radius p T of the target point T , the unit direction vector t A of the starting point direction line, and the unit direction vector t T of the target point direction line;

[0180] The vertical distance calculation formula on the starting point direction line is ​The formula for calculating the perpendicular distance along the target direction line is: .

[0181] The formula for calculating the collision avoidance radius along the starting direction is as follows: The formula for calculating the collision avoidance radius along the target direction line is: .

[0182] Step 3: Calculate the nearest point on the starting point direction line and the nearest point on the target point direction line according to the nearest point calculation method on the direction line.

[0183] Step 4: Substitute the nearest point obtained in Step 3 into the anti-collision radius and perpendicular distance formula in Step 2, compare the calculation results and select the trajectory design type.

[0184] In this embodiment, the perpendicular distance from the starting direction line is... D Amin =71m is greater than the collision avoidance radius d Amin =30m, the perpendicular distance from the target point direction line D Tmin =3m less than the collision avoidance radius d Tmin =30m, using as follows Figure 2 -a shows the double circular arc trajectory profile.

[0185] Step 5: Based on the trajectory design parameters, set the design constraints for the well trajectory to be drilled as follows:

[0186]

[0187] Step 6: Obtain the shale gas development parameters of the block to be drilled, obtain the daily production capacity of the main fracture, and calculate the seepage ellipsoid volume and intersection volume of the main fracture.

[0188] Calculation as Figure 3 The main fracture of the block to be drilled shown P 1. P 2 and P The seepage ellipsoid volumes are respectively A 1. A 2 and A P .

[0189] Obtain the main fracture on the well to be drilled P 1 and P Calculate the intersecting volume using spatial coordinates of 2. B 1 and B 2:

[0190]

[0191]

[0192] The daily production capacity of the main fracture of the infilled well is calculated by petrel fracturing software simulation q 1、 q 2 and q ex , the daily production capacity of the main fracture P q P .

[0193] Step 7: According to the calculation result obtained in step 6, the daily production capacity of the to-be-drilled block is calculated considering the interference effect of the main fracture;

[0194]

[0195] Step 8: Considering the economic benefit of the infilled well, the development cost and income of the to-be-drilled block are calculated; the net present value is taken as the objective function to solve the optimal trajectory length, and the optimization of the obstacle-avoiding trajectory of the infilled well is completed.

[0196] According to the calculation result of step 7, the production capacity in the first t year Q ( t ) can be obtained, and the sales income of production and operation can be expressed as:

[0197]

[0198] Since the obstacle-avoiding trajectory of the to-be-drilled well is designed as a double circular arc trajectory, the development cost of the to-be-drilled well can be expressed as:

[0199]

[0200] The objective function of the optimization model can be expressed as the net present value:

[0201]

[0202] Using the sales income and the development cost, the net present value of the development of the to-be-drilled well under different obstacle-avoiding trajectory lengths is determined, and the relationship curve between the net present value and the obstacle-avoiding trajectory length is shown in Figure 4 .

[0203] The maximum net present value, the corresponding obstacle-avoiding trajectory length is the optimal economic value trajectory length, as shown in Figure 4 , and the optimal economic value obstacle-avoiding trajectory length of the to-be-drilled well is:

[0204]

[0205] In this example, the vertical distance of the point on the designed trajectory and the anti-collision radius changes with the well depth as shown in Figure 5 ​As shown in the figure. With the increase of well depth, the vertical distance of the to-be-drilled well to the main fracture axis decreases; at the well depth of 2300 m, the nearest point of the to-be-drilled well to the fracture risk area is 36 m away from the main fracture axis, and the anti-collision radius is 30 m, so the to-be-drilled well can safely bypass the fracture risk area.

[0206] According to the foregoing trajectory optimization model, the production dynamics of the to-be-drilled block are as shown in the figure. Figures 7-8 The length of the barrier trajectory directly determines the positions of the main fractures P1 and P2, and further affects the intersection area of the percolation ellipsoid. Figure 7 As shown in the comparative diagram of interference effects, the longer the barrier trajectory length, the less the intersection area of the percolation ellipsoid of the main fracture, and the weaker the interference effect. Although the shorter the barrier trajectory length of the to-be-drilled well, the smaller the drilling and completion cost, the trajectory length is not the shorter the better; for a specific formation condition, the longer the barrier trajectory length, the weaker the interference effect of the main fracture, and the greater the productivity of the to-be-drilled block.

[0207] The present application can design the anti-collision trajectory of the wellbore that may enter the risk area by regarding the fracture risk area prone to complex conditions in the to-be-drilled well block as a spatial ellipsoid; convert the influence of the infill well on the productivity of the to-be-drilled block into the intersection problem of the percolation ellipsoid volume, and predict the productivity of the to-be-drilled block according to the interference effect of the main fracture; from the perspective of combining technology and economy, an optimal net present value design method of the barrier trajectory of the infill well is proposed, thereby improving the exploitation benefit of the infill well, and making the determination of the optimal barrier trajectory length more reasonable.

Claims

1. A method of optimizing a trajectory of a well around an obstacle, characterized in that, The method comprises the following steps: Step 1: obtaining microseismic data of a to-be-drilled block, and establishing a fracture risk zone geometric model; Step 2: obtaining information of a starting direction line and a target direction line of a to-be-drilled well, and respectively establishing a vertical distance formula from a point on the starting direction line and the target direction line to a main fracture axis and a collision avoidance radius formula; Step 3: calculating a nearest point from the starting direction line and the target direction line to the fracture risk zone; Step 4: selecting a trajectory design type according to the vertical distance and the collision avoidance radius of the nearest point obtained in step 3; Step 5: obtaining drilling operation restriction conditions of the to-be-drilled block, and setting constraint conditions of a to-be-designed trajectory of the to-be-drilled well; Step 6: obtaining shale gas development parameters of the to-be-drilled block, obtaining a daily production capacity of the main fracture, and calculating a percolation ellipsoid volume and an intersection volume of the main fracture; Step 7: According to the calculation result obtained in Step 6, the daily production capacity of the block to be drilled is calculated considering the main crack interference effect; the daily production capacity of the block to be drilled q sc The calculation method is as follows: wherein, q 1, q 2 and q P are the daily production capacities of the main fractures P 1, P 2 and P q ex are the daily production capacities of the remaining main fractures within the block to be drilled, A 1, A 2 and A P are the seepage ellipsoid volumes of the main fractures P 1, P 2 and P B 1 and B 2 are the intersection volumes of the seepage ellipsoids of the adjacent main fractures;​​ Step 8: Considering the economic benefits of the infill well, the development cost and income of the block to be drilled are calculated; the net present value is taken as the objective function to solve the optimal trajectory length, and the optimization of the infill well trajectory around the obstacle is completed; the income CI is the cash inflow, and its calculation method is as follows: Wherein: CI (1) is the cash inflow in the first year, t t W r is the commodity rate of natural gas, P is the natural gas sales price, Q t (1) is the productivity of the block to be drilled in the first year, t the second year.​​​ Development costs CO Cash outflows are calculated as follows: wherein: CO ( t ) is the cash outflow in the year of 2018, t C s is the drilling cost per unit length of the well to be drilled, L h is the linear segment trajectory length of the well to be drilled, L is the trajectory length of the obstacle-avoiding segment of the well to be drilled, C f is the volume fracturing cost, C Mg is the operating cost per unit gas production.​ The objective function is as follows: where: NPV NPV is the net present value, n t is the project evaluation period, j r is the annual discount rate.

2. The method of claim 1, wherein, The fracture risk zone geometric model construction method in step 1 is as follows: According to the microseismic data, fracture characteristics of a drilled well volume fracturing are obtained; the fracture characteristics include main fracture distribution information and fracture scale information; end point of the main crack axis M 0 vector radius p0, α 0 inclination angle, φ 0 azimuth angle, unit direction vector t0; The crack geometric model is a spatial ellipsoid, and the axis lengths of the ellipsoid are a , b , c .

3. The method of claim 2, wherein, The vertical distance formula from a point on the starting direction line to the main fracture axis and the collision avoidance radius formula are constructed as follows: Origin A The vector magnitude of the origin point is p A , the inclination angle of the direction line is α A , the azimuth angle is φ A , and the unit direction vector is t A ; the target point T The vector magnitude of the target point is p T , the inclination angle of the direction line is α T , the azimuth angle is φ T , and the unit direction vector is t T ; The vectorial range of the point with the well depth of s on the starting point direction line is obtained M , and the perpendicular to the main fracture axis is made M , and the foot point is MM A , and the foot point is M A ; the perpendicular distance from a point on the origin direction line to the main fracture axis D A The calculation formula is as follows: wherein: is a straight line MM direction vector of 0; Target point direction online point to the vertical distance from the main fracture axis D T Computational methods as D A Computational methods; Computing M A the length of the semi-major axis of the cross-sectional ellipse a A and the length of the semi-minor axis b A ; Computing the perpendicular MM A and the intersection coordinates of the cross-section ellipse x A , y A ); A point on the start direction line and the anti-collision radius of the crack risk area d A The calculation formula is as follows: 。 4. The method of claim 3, wherein, The calculation method of the nearest point from the starting direction line to the fracture risk zone is as follows: If M The starting point is the nearest point on the direction line to the fracture risk zone, according to the function extreme condition: From the above equation, the equation for the well depth s is obtained, and from the equation for the well depth s the coordinates of the nearest point on the starting direction line are obtained.

5. The method of claim 4, wherein, The trajectory design type selection method is as follows: Calculate perpendicular distance of the closest point on the start direction line D Amin and the collision avoidance radius d Amin , the closest point on the target direction line D Tmin and the collision avoidance radius d Tmin ; If D Amin Less than d Amin Or D Tmin Less than d Tmin The obstacle trajectory adopts a double circular arc trajectory model. If D Amin Less than d Amin And D Tmin Less than d Tmin The obstacle trajectory adopts a three-arc trajectory model.

6. The method of claim 5, wherein, The drilling operation restriction conditions include a target centering accuracy, a borehole curvature, a well section length and a collision avoidance constraint; The target centering accuracy of the drilling operation satisfies: in, N is the number of well sections, i For well section labeling, , , The first i well section in X , Y , Z Increment in direction , , These are the starting points of the well to be drilled. A With target T exist X , Y , Z Coordinate difference on the coordinate system δ The acceptable error value, L i It is the first i The length of the well section, For the first i Rate of change of well inclination angle in the well section For the first i azimuth rate of change of well section α The well inclination angle, φ It is the azimuth angle. This represents the change in well inclination angle. This represents the change in azimuth angle; The borehole curvature of the circular arc section trajectory satisfies: wherein, is the i a wellbore curvature limit value for the well section, k i is the i a wellbore curvature for the well section, Each well section length satisfies: in, For the first i Minimum well section length, For the first i The maximum length of the well section, L i For the first i The length of the well section; The collision avoidance constraint of the designed trajectory, that is, each well section does not collide with the fracture risk zone; If there is any i well section d imin D imin The trajectory around the obstacle needs to be redesigned until all well sections can safely avoid the fracture risk zone.​ 7. The method of claim 6, wherein, The intersection volume of the main fractures B 1The calculation method is as follows: where, F x are functions of the overlapping volume, P 1 is the main fracture P adjacent to the infill well, φ 0 is the azimuth of the main fracture, A 1 and A P are the permeability ellipsoid volumes of the main fracture P 1 and P adjacent to the infill well, respectively.​

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