Real-time evaluation method and system for shale oil drilling sweet spot

Abstract

This invention provides a method and system for real-time evaluation of sweet spots in shale oil drilling. The method includes: establishing a first drilling time model based on parameters such as drill bit wear coefficient, drilling pressure, rotation speed, drilling fluid properties, formation brittleness, and oil content; then obtaining the mathematical relationship between drilling time and formation brittleness and oil content; establishing a second drilling time model; subsequently obtaining the theoretical values ​​of drilling time before and after the drill bit enters the window; drilling before the window is entered based on the theoretical values ​​of drilling time before the window is entered, and adjusting the drill bit position until the window is entered; drilling after the window is entered based on the theoretical values ​​of drilling time after the window is entered, and adjusting the drill bit position. This invention quantitatively evaluates the drill bit wear coefficient, ensuring stable drilling pressure, rotation speed, and drilling fluid properties under normal drilling conditions; establishing a mathematical model between real-time rotation speed and formation brittleness and oil content; and using logging cuttings and gas logging information to determine the lithology and oil and gas content at the drill bit location in real time, thereby minimizing the target distance and improving the sweet spot encounter rate.

Description

Technical Field

[0001] This invention belongs to the field of petroleum exploration technology, and specifically relates to a method and system for real-time evaluation of shale oil sweet spots during drilling. Background Technology

[0002] The shale oil revolution abroad has achieved tremendous success, realizing self-sufficiency in oil and gas supply. Shale oil has become one of the important replacement areas for conventional oil and gas resources, possessing significant socio-economic value. While overseas marine shale oil and gas exploration and development has accumulated rich experience, continental shale sweet spots are characterized by rapid vertical variations, poor lateral continuity, and uneven distribution of resource grades, which restricts the industrial development of shale oil in my country. Related core technologies are still in the experimental and research stage. Sweet spot evaluation is one of the key technologies in shale oil exploration and development, playing a crucial role in shale oil pre-exploration, evaluation, and production establishment. Currently, shale oil sweet spot evaluation mainly relies on post-drilling sweet spot evaluation based on core, well logging, and seismic data. The methodology, based on core data, various test and analysis data, and well logging data, aims to comprehensively evaluate the grade of sweet spots in drilled shale oil wells and, combined with seismic data, predict the spatial distribution patterns of sweet spots. However, the vertical resolution of seismic data is only about 30-40 meters, the logging-while-drilling delay is about 15 meters, and the cuttings logging delay is generally 1-2 hours. Existing technologies have the characteristics of low resolution and information lag. How to achieve real-time evaluation of shale oil sweet spots is a problem currently faced by shale oil exploration and development. Summary of the Invention

[0003] To address the above problems, this invention proposes a method and system for real-time evaluation of shale oil drilling sweet spots.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for real-time evaluation of shale oil drilling sweet spots includes the following steps:

[0006] The first drilling time model was established based on parameters such as drill bit wear coefficient, drilling pressure, rotation speed, drilling fluid properties, formation brittleness, and oil content.

[0007] The drill bit wear coefficient in the first drilling time model was quantitatively determined, and the drilling pressure, rotation speed and drilling fluid performance conditions were stabilized to obtain the mathematical relationship between drilling time and formation brittleness and oil content, and to establish the second drilling time model.

[0008] The theoretical values ​​of drilling time before and after the drill bit enter the window are obtained based on the second drilling time model.

[0009] Drill before the window is entered based on the theoretical value of the drilling time before the window is entered, and adjust the drill bit position until the window is entered;

[0010] Drilling is performed after entering the window based on the theoretical value of drilling time, and the drill bit position is adjusted.

[0011] Preferably, the relationship of the first drilling time model is as follows:

[0012] ZS=a×(1-Ad)+b×Bp+c×Rs+d×D f +e×Li+f×Oi+z;

[0013] Where ZS is drilling time, min / m; Ad is the drill bit wear coefficient, dimensionless; a is the influence coefficient of the drill bit on drilling time under wear conditions, min / m; Bp is drilling pressure, kN; b is the influence coefficient of drilling pressure on drilling time, min / m·kN; Rs is rotational speed, rpm; c is the influence coefficient of rotational speed on drilling time, min / m·rpm; D f denoted as drilling fluid properties, dimensionless; d is the drilling time influence coefficient of standard drilling fluid under formation conditions, min / m; Li is the formation brittleness index, dimensionless; e is the influence coefficient of formation brittleness index on drilling time, min / m; Oi is oil abundance, mg / g; f is the influence coefficient of oil abundance on drilling time, min / m·mg / g; z is the corrected drilling time, min / m.

[0014] Preferably, the relationship between the drilling fluid properties is as follows:

[0015]

[0016] Among them, D f The drilling fluid properties are dimensionless; Δv' is the actual change in drilling fluid volume in the well, in meters. 3 Δv is the change in drilling fluid volume, m 3 .

[0017] Preferably, the relationship of the second drilling time model is as follows:

[0018] ZS = e×Li + f×Oi + Z;

[0019] Where ZS is the drilling time, min / m; Li is the brittleness index of the rock formation, dimensionless; e is the influence coefficient of the brittleness index of the rock formation on the drilling time, min / m; Li is the brittleness index of the rock formation, dimensionless; Oi is the oil abundance, mg / g; f is the influence coefficient of the oil abundance on the drilling time, min / m·mg / g; Z is the corrected drilling time, min / m.

[0020] Preferably, both the drilling pressure and the rotational speed are inversely proportional to the drilling time.

[0021] Preferably, drilling before the window is entered is performed based on the theoretical value of the drilling time before the window is entered, and the drill bit position is adjusted until the window is entered, including the following steps:

[0022] Divide the drilling route 160m before the window into n segments, where n≥2. Starting from the i-th segment, select 5-10 sample points at 2-meter intervals, where n≥i≥1, and collect rock cuttings.

[0023] Based on the lithology analysis of the depth corresponding to the cuttings, the cuttings are repositioned using theoretical values ​​during drilling before the window is entered, and the formation brittleness index corresponding to the lithology is found.

[0024] A third drilling time model was established based on the second drilling time model and the formation brittleness index;

[0025] Adjust the drill bit position based on the third drilling time model until it enters the window.

[0026] Preferably, the relationship of the third drilling time model is as follows:

[0027] ZS = e i ×Li i +Z i ;

[0028] Among them, e i Li is the influence coefficient of the brittleness index of the i-th stratum on drilling time, in min / m; i Z is the brittleness index of the i-th rock stratum, dimensionless; i The corrected drilling time (min / m) for the i-th segment before entering the window, under controlled drilling pressure, rotation speed, and drilling fluid properties.

[0029] Preferably, drilling after entering the drilling window is performed based on the theoretical value of drilling time after entering the window, and the drill bit position is adjusted, including the following steps:

[0030] After entering the window, the drill bit enters the sweet spot box. In the sweet spot box, 5-10 sample points are selected at 1-meter intervals to collect rock cuttings.

[0031] Data on the lithology, brittleness index, and oil content of rock cuttings are obtained, and then the data are substituted into the second model to obtain the calculation results;

[0032] The calculation results are compared with the theoretical values ​​for drilling after entering the window. Then the drill bit position is determined. If the drill bit is outside the dessert box, the drill bit is adjusted back to the dessert box. Otherwise, the drill bit position changes are tracked.

[0033] A system corresponding to a method for real-time evaluation of shale oil drilling sweet spots includes a comprehensive module, a quantitative module, an analysis module, a first calculation module, and a second calculation module;

[0034] The integrated module is used to establish a first drilling time model based on parameters such as drill bit wear coefficient, drilling pressure, rotation speed, drilling fluid properties, formation brittleness, and oil content.

[0035] The quantitative module is used to quantify the drill bit wear coefficient in the first drilling time model, stabilize the drilling pressure, rotation speed and drilling fluid performance conditions, obtain the mathematical relationship between drilling time and formation brittleness and oil content, and establish the second drilling time model.

[0036] The analysis module is used to obtain the theoretical values ​​of the drilling time before and after the drill bit enters the window based on the second drilling time model.

[0037] The first calculation module is used to perform pre-drilling based on theoretical values ​​during pre-drilling and to adjust the drill bit position until the window is entered.

[0038] The second calculation module is used to perform drilling after entering the window based on the theoretical value of drilling after entering the window, and to adjust the drill bit position.

[0039] Preferably, the first computing module includes a first collection unit, an analysis unit, a construction unit, and a first adjustment unit;

[0040] The first collection unit is used to divide the drilling route 160m before the window into n segments, where n≥2. Starting from the i-th segment, 5-10 sample points are selected at 2-meter intervals, where n≥i≥1, to collect rock cuttings.

[0041] The analysis unit is used to analyze lithology based on the depth of the cuttings, use theoretical values ​​from the pre-drilling window to reposition the cuttings, and find the formation brittleness index corresponding to the lithology.

[0042] The building unit is used to establish a third drilling time model based on the second drilling time model and the formation brittleness index;

[0043] The first adjustment unit is used to adjust the drill bit position based on the third drilling time model until it enters the window.

[0044] Preferably, the second calculation unit includes a second collection unit, a calculation unit, and a second adjustment unit;

[0045] The second collection unit is used to collect rock cuttings by selecting 5-10 sample points at 1-meter intervals in the sweet spot box after the drill bit enters the sweet spot box through the entry window.

[0046] The calculation unit is used to acquire data on the lithology, brittleness index, and oil content of rock cuttings, and then substitute the data into the second model to obtain the calculation results.

[0047] The second adjustment unit is used to compare the calculation results with the theoretical value of drilling after entering the window, and then determine the position of the drill bit. If the drill bit is outside the dessert box, the drill bit is adjusted back to the dessert box; otherwise, the drill bit position changes are tracked.

[0048] The beneficial effects of this invention are:

[0049] 1. This invention quantitatively evaluates the drill bit wear coefficient to meet the conditions of stable drilling pressure, rotation speed and drilling fluid performance under normal drilling conditions. It establishes a mathematical model between real-time rotation speed and formation brittleness and oil content, and uses logging cuttings and gas logging information to determine the lithology and oil and gas content of the drill bit location in real time, thereby minimizing the target distance and improving the sweet spot drilling rate.

[0050] 2. The drilling time of shale formations in this invention is jointly controlled by geological and engineering conditions. By optimizing the parameters affecting drilling time, a formation drilling time response model is established. Various engineering parameters are gradually controlled, optimized, and stabilized. A mathematical model between rotation speed and formation brittleness and oil content is established in real time. Drilling time is used to reflect the lithology and oil content of the formation at the drill bit location. Its prediction accuracy is 15 meters ahead of logging-while-drilling data and 1-2 hours ahead of cuttings logging and gas logging information.

[0051] 3. The shale oil prediction sweet spot box depth, thickness, dip, dip angle and other information of the present invention have certain errors with its actual occurrence. By evaluating the sweet spot in real time, a standardized drilling process and technology before and after entering the window can be established, which can effectively reduce the drilling cycle, reduce the intensity of on-site formation comparison work, and realize the factory-style drilling process of shale oil horizontal wells.

[0052] 4. After entering the window, the process of this invention controls the engineering conditions, and by predicting the change range of drilling time in the box by the relationship between drilling time and formation lithology and oil content, it can achieve rapid drilling in the sweet spot and effectively reduce the drilling cycle.

[0053] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 A process flow diagram of the real-time evaluation method for shale oil drilling sweet spots according to the present invention is shown;

[0056] Figure 2 A schematic diagram showing the loss of drilling capacity when the drill bit has drilled a certain distance is shown;

[0057] Figure 3 A simplified diagram illustrating the drilling capacity loss of the drill bit is shown;

[0058] Figure 4 The graph shows the relationship between shale drilling time and oil abundance;

[0059] Figure 5 The horizontal entry trajectory 1 for shale oil corresponding to Example 1 is shown;

[0060] Figure 6 The horizontal entry trajectory 2 for rock oil corresponding to Example 2 is shown;

[0061] Figure 7 A structural diagram of a real-time evaluation system for shale oil drilling sweet spots is shown. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] A method for real-time evaluation of shale oil drilling sweet spots, such as Figure 1 As shown, it includes the following steps:

[0064] S1: Establish the first drilling time model based on parameters such as drill bit wear coefficient, drilling pressure, rotation speed, drilling fluid properties, formation brittleness, and oil content;

[0065] S2: Quantify the drill bit wear coefficient in the first drilling time model, stabilize the drilling pressure, rotation speed and drilling fluid performance conditions, obtain the mathematical relationship between drilling time and formation brittleness and oil content, and establish the second drilling time model;

[0066] S3: Based on the second drilling time model, obtain the theoretical values ​​of drilling time before and after the drill bit enters the window;

[0067] S4: Drill before the window is entered based on the theoretical value of the drilling time before the window is entered, and adjust the drill bit position until the window is entered;

[0068] S5: Drill after entering the window based on the theoretical value of drilling time after entering the window, and adjust the drill bit position.

[0069] Furthermore, the relationship of the first drilling model is as follows:

[0070] ZS=a×(1-Ad)+b×Bp+c×Rs+d×D f +e×Li+f×Oi+z;

[0071] Where ZS is drilling time, min / m; Ad is the drill bit wear coefficient (value 1 for new drill bits, 0 for fully worn drill bits), dimensionless; a is the influence coefficient of the drill bit on drilling time under wear conditions, min / m; Bp is drilling pressure, kN; b is the influence coefficient of drilling pressure on drilling time, min / m·kN; Rs is rotational speed, rpm; c is the influence coefficient of rotational speed on drilling time, min / m·rpm; D f denoted as drilling fluid properties, dimensionless; d is the drilling time influence coefficient of standard drilling fluid under formation conditions, min / m; Li is the formation brittleness index, dimensionless; e is the influence coefficient of formation brittleness index on drilling time, min / m; Oi is oil abundance, mg / g; f is the influence coefficient of specific oil abundance and specific conditions on drilling time, min / m·mg / g; z is the corrected drilling time (the influence of human or other unknown factors on drilling time), min / m.

[0072] It should be noted that in the formula, drill bit wear coefficient, pressure on drill bit (PBD), rotation speed, and drilling fluid properties are controllable or estimable drilling parameters, while formation brittleness and oil content are formation parameters. Drilling time is jointly controlled by both drilling and formation parameters; a change in any parameter will alter the drilling time. The influence of drilling parameters on drilling time is linear: as the drill bit wear coefficient increases, drilling time tends to decrease; increases in PBD, rotation speed, and improved drilling fluid properties also decrease drilling time. Changes in lithology and oil content have a non-linear influence on drilling time, and changes in lithology or oil content will alter the influence coefficients of parameters such as PBD and rotation speed on drilling time. During the establishment of the drilling time model, drilling parameters, formation parameters, and their influence coefficients are constantly changing. During drilling, these parameters should be adjusted promptly based on the actual underground conditions to form a dynamic model of drilling time during drilling.

[0073] Furthermore, the drill bit wear coefficient is related to the brittleness of the exposed strata and its diagenetic evolution degree. Sandstone and conglomerate rocks have higher drill bit wear coefficients than mudstone and shale, and lithologies with higher diagenetic evolution degrees have relatively higher drill bit wear resistance. The drill bit wear coefficient can be evaluated using quantitative evaluation methods, such as... Figure 3 As shown, the wear of a drill bit is directly proportional to the formation thickness and Young's modulus, and the lifespan of a drill bit is controlled by both factors. Assume that a certain type of drill bit can drill a distance *d* in a homogeneous rock formation, and the Young's modulus of the homogeneous formation is *E*. When the Young's modulus of the formation increases, the drilling distance of the drill bit decreases; when the Young's modulus of the rock formation decreases, the drilling distance of the drill bit increases. The drilling capacity of the drill bit is defined as the integral of the Young's modulus of the drill bit in the drillable formation, denoted by AC: AC = Ed. Where: AC is the drilling capacity of a certain type of drill bit (m·GPa); is the Young's modulus of the standard rock (GPa); d is the drilling distance of a certain type of drill bit in the standard rock formation.

[0074] During drilling, as the drilling distance increases, the drilling capacity of the drill bit decreases. The drilling capacity loss of the drill bit after drilling a certain distance is denoted as Ac, and the relationship is as follows:

[0075]

[0076] Where: Ac is the drilling capacity lost when the drill bit travels a distance of x, in meters·Gpa; E(x) is the Young's modulus of the rock strata at any drilling depth, in GPa; Ax is the drilling length, in meters.

[0077] like Figure 2 As shown, the lithology encountered during drilling is layered, and the drilled strata can be divided into layers y, with the rock brittleness index corresponding to layer j being E. j Then the formula for calculating the drilling capacity loss of the drill bit can be simplified to:

[0078] Ultimately, the relationship between the wear levels of the drill bit and the following formula is used:

[0079]

[0080] Where Ad is the drill bit wear coefficient, dimensionless; AC is the drill bit's drilling capacity, meters·Gpa; and Ac is the drilling capacity lost by the drill bit after drilling a certain distance, meters·Gpa.

[0081] It should be noted that the drill bit wear coefficient can also be determined using an empirical formula, as follows: Within the same depression or slope area, where the lithological combination characteristics of the strata are similar and the diagenetic evolution stages are the same, the drill bit always wears down during drilling. Therefore, the wear degree of the drill bit being drilled can be estimated based on the service life of drill bits already drilled in the study area. Suppose the maximum drilling length of a certain type of drill bit in the study area is A. max Meters, the depth drilled by the drill bit to be evaluated is A. r The relationship is as follows:

[0082]

[0083] Where Ad is the drill bit wear coefficient; A max A is the maximum drilling length. r This represents the depth to which the drill bit has reached.

[0084] Furthermore, drilling fluids primarily function to clean the bottom of the hole, cool the drill bit, lubricate the drill string, and protect the borehole wall. Maintaining the stability of drilling fluid performance is one of the key indicators for evaluating shale sweet spots. Drilling fluid performance affects drilling speed, and when drilling speed changes, drilling fluid performance changes accordingly; the two are mutually causal and influence each other gradually. Once drilling fluid performance is stabilized, drilling time information can more accurately reflect the geological information at the drill bit's location.

[0085] During drilling, as drilling time decreases, drilling speed increases, drill bit temperature rises, and the amount of cuttings at the bottom of the well increases, necessitating an increase in drilling fluid inlet flow rate to maintain drilling fluid performance stability. Once the drilling fluid density, viscosity, and other conditions meet drilling requirements, the drilling fluid formula is stabilized, drilling circulation is set up, and cuttings at the bottom of the well are removed. The drilling fluid pump inflow rate after drilling begins is denoted as W. in (m 3 The outflow rate is denoted as W / min. out (m 3 / min). The pump inflow rate is related to the drilling fluid's ability to cool the drill bit. As drilling time increases, the heat generated by friction between the drill bit and the rock increases, requiring a larger volume of drilling fluid to cool it. An increase in outlet flow rate indicates an enhanced sand-carrying capacity of the drilling fluid. Drilling time, pump inflow rate, and outlet flow rate satisfy the following relationship:

[0086] W in =k / ZS;

[0087] W out =j / ZS;

[0088] Under standard conditions, the relationship coefficients k and j between drilling time and pump inflow rate and outlet flow rate are determined by reading the drilling time, pump inflow rate and outlet flow rate values.

[0089] Pump inflow rate (m 3 ), export flow (m 3 ), Change in drilling fluid volume Δv (m 3 The following relationship exists between ) and the time change Δt(min):

[0090] W out =W in +Δv / Δt;

[0091] Then we have:

[0092] J / ZS=kZS / +Δv / Δt;

[0093] Δv / Δt=(kj) / ZS;

[0094] With Δt set to 1 min, the change in the volume of drilling fluid in the well is: Δv=(kj) / ZS;

[0095] In the formula, k and j are constants. When the change in the volume of the drilling fluid in the well pool, Δv, satisfies the above relationship with the drilling time, the drilling fluid performance is stable.

[0096] Finally, the relationship between drilling fluid properties is as follows:

[0097]

[0098] Among them, Df The drilling fluid properties are dimensionless; Δv' is the actual change in drilling fluid volume in the well, in meters. 3 Δv is the change in drilling fluid volume, m 3 .

[0099] Furthermore, under the conditions of constant drill bit wear coefficient, drilling pressure, rotational speed, and drilling fluid properties, the relationship of the second drilling time model is as follows:

[0100] ZS = e×Li + f×Oi + Z;

[0101] Where ZS is the drilling time, min / m; Li is the brittleness index of the rock formation, dimensionless; e is the influence coefficient of the brittleness index of the rock formation on the drilling time, min / m; Li is the brittleness index of the rock formation, dimensionless; Oi is the oil abundance, mg / g; f is the influence coefficient of specific oil abundance and specific conditions on the drilling time, min / m·mg / g; Z is the corrected drilling time, min / m.

[0102] It should be noted that, without considering oil-bearing conditions, drilling time is mainly affected by the formation brittleness index. Formations with a high brittleness index have lower drilling time, while formations with a low brittleness index have higher drilling time.

[0103] The rock brittleness index can be obtained from engineering mechanics tests of core wells in the study area. For areas without relevant data, the distribution range of lithological brittleness index for shale formations is shown in Table 1.

[0104] Table 1: Formation Brittleness Index Table

[0105] Lithology Brittleness index (Li) distribution range sandstone 68.3-90.4 felsic shale 55.8-70.6 clay shale 16.6-31.2 carbonate shale 40.4-45.6 limestone 32.1-41.8 Dolomite 45.4-53.5 carbonate mixed shale 38-42.4 Felsic mixed shale 43.64-56.75 clayey mixed shale 32.25-40.7

[0106] During drilling, by recording drilling time and logging lithology data, the brittleness index (Li) corresponding to different lithologies is found. Substituting this into the formula ZS=e×Li+f×Oi+Z, the influence coefficient f on drilling time under specific oil abundance and specific conditions can be determined using the multiple regression method.

[0107] like Figure 4 As shown, this illustrates the effect of oil content (oil abundance) on drilling time. Oil-bearing shale reduces rock friction resistance, and as oil abundance increases, shale drilling time generally decreases exponentially.

[0108] For the same lithology, if drilling time shows a regular decreasing trend, it indicates an increase in formation oil abundance. Similarly, multiple regression methods can be used to determine the influence coefficient f of specific oil abundance and drilling time under specific conditions.

[0109] During horizontal well entry or horizontal section tracking, when the drilling time variation exceeds the set value, a circulation command is issued in a timely manner. The lithology and oil and gas properties of the drill bit location are determined in real time through logging cuttings and gas logging information, so as to minimize the target distance and improve the sweet spot drilling rate.

[0110] Furthermore, both drilling pressure and rotational speed are inversely proportional to drilling time.

[0111] It should be noted that drill pressure and rotation speed are controllable parameters and can be adjusted according to the site environment, formation conditions, and drilling plan. During the first 150 meters before entering the window of a horizontal well and during drilling within the sweet spot, to achieve real-time evaluation of the sweet spot, the stability of drill pressure and rotation speed should be maintained to reduce systematic errors and improve the accuracy of prediction results.

[0112] Furthermore, S4 includes the following steps:

[0113] Divide the drilling route 160m before the window into n segments, where n≥2. Starting from the i-th segment, select 5-10 sample points at 2-meter intervals, where n≥i≥1, and collect rock cuttings.

[0114] Based on the lithology analysis of the depth corresponding to the cuttings, the cuttings are repositioned using theoretical values ​​during drilling before the window is entered, and the formation brittleness index corresponding to the lithology is found.

[0115] A third drilling time model was established based on the second drilling time model and the formation brittleness index;

[0116] Adjust the drill bit position based on the third drilling time model until it enters the window.

[0117] Furthermore, the relationship of the third drilling model is as follows:

[0118] ZS = e i ×Li i +Z i ;

[0119] Among them, e i Li is the influence coefficient of the brittleness index of the i-th rock stratum on drilling time, in min / m; i Z is the brittleness index of the i-th rock stratum, dimensionless; i The corrected drilling time (min / m) for the i-th segment before entering the window, under controlled drilling pressure, rotation speed, and drilling fluid properties.

[0120] Let's take i=1 and 2 as examples to explain step S4:

[0121] When i=1, 150-160 meters before entering the drilling window, control the drilling pressure and rotation speed, and stabilize the drilling fluid properties. After the cuttings return to the surface, select 5-10 sample points at 2-meter intervals, analyze the lithology based on the depth corresponding to the cuttings, use the theoretical drilling time curve before entering the window to reposition the cuttings, and find the brittleness index corresponding to the lithology. Before entering the window, the formation has low oil content. Under the condition of controlling the drilling pressure, rotation speed, and drilling fluid properties, the rotation time is mainly controlled by the lithological conditions. At this time, the third drilling time model is:

[0122] ZS = e1 × Li1 + Z1;

[0123] Where e1 is the influence coefficient of the brittleness index of the first rock stratum on drilling time, min / m; Li1 is the brittleness index corresponding to the first rock stratum, dimensionless; Z1 is the corrected drilling time of the first section before entering the window, under the conditions of controlling drilling pressure, rotation speed and drilling fluid performance, min / m.

[0124] Then, when i=2, repeat the above steps 100-110 meters before entering the window, using 2-meter intervals to select 5-10 sample points, determine the corresponding depth, lithology and brittleness index of the sample, and at this time the third drilling time model formula can be recorded as ZS=e2×Li2+Z2. Substitute the obtained measurement point data into the formula to obtain the values ​​of e2 and Z2.

[0125] Calculate the relative error δe between e1 and e2, δe = 2(e1-e2) / (e1+e2); calculate the relative error δZ between Z1 and Z2, δZ = 2(Z1-Z2) / (Z1+Z2). When both δe and δZ are less than 0.1, it indicates a good response relationship between drilling time and formation brittleness index. The formation brittleness index at the drill bit location can be reflected by drilling time, so Li = (ZS-Z2) / e2. In Table 1, the lithology corresponding to the brittleness index value can be found to determine the lithology at the drill bit location in real time. If both δe and δZ are greater than 0.1, it indicates that the established formula cannot accurately reflect the underground information. It is necessary to re-enter the cycle, clean the wellbore, strictly control the engineering parameters and drilling fluid performance, drill another 10m, and obtain the e3 and Z3 values ​​within 90-100m before the window. Calculate the δe and δZ values ​​again until both δe and δZ are less than 0.1.

[0126] Once both δe and δZ values ​​are less than 0.1, maintain drilling pressure, rotation speed, and drilling fluid properties for smooth drilling. Based on the predicted sweet spot depth and relative error value, when the drill bit approaches the predicted sweet spot depth error range, monitor the change in the drilling time baseline value. When the drilling time decreases by more than 20%, promptly pause drilling and enter circulation mode. Wait until the cuttings and gas logging data are returned to the surface. If the cuttings contain oil at the level of oil traces or oil spots, it indicates that the drill bit has entered the sweet spot. Adjust the well inclination angle, such as... Figure 5As shown, the well inclination angle is kept consistent with the inclination angle of the dessert box, and the drilling is carried out at a stable angle.

[0127] Furthermore, S5 includes the following steps:

[0128] After entering the window, the drill bit enters the sweet spot box. In the sweet spot box, 5-10 sample points are selected at 1-meter intervals to collect rock cuttings.

[0129] Data on the lithology, brittleness index, and oil content of rock cuttings are obtained, and then the data are substituted into the second model to obtain the calculation results;

[0130] The calculation results are compared with the theoretical values ​​for drilling after entering the window. Then the drill bit position is determined. If the drill bit is outside the dessert box, the drill bit is adjusted back to the dessert box. Otherwise, the drill bit position changes are tracked.

[0131] The steps of S5 are explained in detail below:

[0132] After entering the sweet spot, maintain drilling pressure, rotation speed, and drilling fluid properties for stable drilling. At this stage, drilling time is mainly controlled by formation lithology and oil content. The drilling time response model is simplified to: ZS = e × Li + f × Oi + Z. After the cuttings return to the surface, select 5-10 sample points at 1-meter intervals to obtain the lithology, brittleness index, and oil content of the cuttings at the corresponding depth. Substitute the obtained measurement data into the formula to calculate the values ​​of e3, f3, and Z3. When the oil content is lower than a certain set value, it indicates that the drill bit has exited the sweet spot box. After setting a threshold, determine the normal range of drilling time variation within the box based on the lithology and its combination within the box. During the sweet spot box tracking process, if the drilling time exceeds the normal range, stop drilling immediately and enter a circulation state. After the cuttings return to the surface, determine the location of the drill bit in the sweet spot box based on the measured oil content of the cuttings. If the oil content of the cuttings changes, it indicates that the drill bit has exited the formation and the well inclination angle needs to be adjusted in time to allow the drill bit to return to the sweet spot box as soon as possible.

[0133] Finally, repeat the above process until the drilling is complete.

[0134] The following explains the dessert evaluation process for the specific research area:

[0135] Example 1

[0136] Real-time evaluation of the sweet spot before entry window and drilling decisions for shale oil horizontal wells, as detailed below:

[0137] 1. Geological Background. In a certain study block, two sweet spots were identified vertically through systematic evaluation. The purpose of this drilling is to explore the oil-bearing capacity and production capacity of sweet spot 1. The designed well trajectory is shown in the attached diagram. Figure 5As shown, the lithology within the sweet spot section is mainly carbonate shale interbedded with thin layers of dolomite. Each sweet spot section is topped by a stable dolomite layer, which can be used as a marker layer. To achieve the drilling objectives, the method and system provided by this patent are used during drilling to evaluate the shale oil sweet spots in real time, and the evaluation results guide the horizontal well trajectory adjustment process.

[0138] 2. Collect drilling parameters 150 meters before the entry window. The predicted sweet spot depth of this well is 3590 meters. At a depth of 3450 meters, the corresponding drilling time is 7.6 min / m, drilling pressure is 137.62 kN, and drilling speed is 23.1 rpm; the drilling fluid equivalent density is 1.32 g / cm³. 3 Inlet flow rate: 2.3m 3 / min, outlet flow rate 2.2m 3 / min, inlet density 1.26g / cm³ 3 Export density 1.27 g / cm³ 3 The total pool volume is 111.36 m³. 3 The drilling pressure was stabilized at approximately 137.62 kN, the drilling speed at approximately 23.1 rpm, the drilling fluid density at 1.32, the drilling fluid viscosity at 43, and the drilling fluid inlet flow rate at 2.3 m³ / h. 3 / min.

[0139] Samples were taken at 2-meter intervals, with a total interval of 10 meters between 3450 and 3440. Statistical analysis revealed that the content of felsic minerals in this stratum ranged from 33% to 43% (average 37.62%), carbonate minerals from 29% to 36% (average 31.71%), and clay minerals from 19% to 28% (average 23.29%). The lithology included two types: felsic mixed shale and carbonate mixed shale. According to Appendix Table 1, the brittleness index of this stratum ranged from 38 to 56.75. The TOC (total organic carbon) from mudstone pyrolysis during drilling ranged from 1.72% to 2.12% (average 1.86%), and the S1 content ranged from 0.67 mg / g to 0.9 mg / g (average 1.86 mg / g). The calculated oil saturation index ranged from 56.55 to 66.89 mg / g TOC (average 61.58 mg / g TOC). The formation in the 3450-3440 meter well section had poor oil-bearing properties. Under certain drilling parameters, drilling time was mainly controlled by lithology. The drilling time and formation brittleness index satisfy the following calculation formula: ZS = d × Li + Z (d is the influence coefficient of drilling time under certain brittleness index and specific conditions, min / m; Li is the brittleness index of the formation, dimensionless; Z is the corrected drilling time, min / m). Calculations show that the theoretical drilling time for this formation section is 9-13 min / m.

[0140] 3. 100 meters before the window is reached, drilling parameters are collected again. Calculations show that the theoretical drilling time for the formation in the 3590-3600 meter section is 8-12 min / m. The relative error is 0.06, meeting the criteria, and the drilling time information reflects the lithology at the drill bit's location. At a depth of 3400 meters, data collection shows the theoretical drilling time should be 8.5-13 min / m. Approaching the sweet spot, the drilling time shows an increasing trend, possibly due to inadequate removal of downhole cuttings, altering drilling fluid properties. At this point, a circulation command is issued to continue drilling. Data is collected again at a depth of 3410-3420 meters, calculating the theoretical drilling time to be 7-11 min / m. Maintaining a drill pressure of 137.62 kN, rotation speed of 23.1 rpm, drilling fluid density of 1.32, and drilling fluid viscosity of 43, drilling continues, awaiting the window.

[0141] 4. Determining the Entry Window. When drilling reached 3445.5 meters, the drilling time suddenly increased from 9 min / m to 16 min / m, exceeding the theoretical drilling time. This indicated a change in lithology, prompting a stop drilling command and initiating a cycle to await the return of cuttings and gas logging data to the surface. On-site whole-rock X-ray diffraction analysis confirmed the drill bit's location as dolomite, confirming that the drill bit had reached the predicted sweet spot 1 location for shale oil. Conventional sweet spot evaluation methods require 15 meters of normal drilling to determine the entry window location. This method, while ensuring accurate entry into the window for shale oil horizontal wells, effectively saves 15 meters of drilling footage, reduces the target distance, and increases the utilization rate of geological sweet spots.

[0142] Example 2

[0143] Shale oil horizontal well horizontal section trajectory control and efficient drilling, as detailed below:

[0144] After well entry, on-site logging data showed that the sweet spot contained 24.66% felsic minerals, 51.33% carbonate minerals (41.66% dolomite, 9.67% calcite), and 18.66% clay minerals. The rock was identified as gray dolomitic limestone. On-site measurements showed a TOC of 2.34%, equivalent oil content of 41.57%, a correlation grade of 6.9, an oil saturation index of 66.8 mg / g TOC, and a total hydrocarbon value of 1.5%. Based on the comprehensive oil and gas indication characteristics, this sweet spot was classified as a Class III oil layer. The original design, after reaching sweet spot 1, increased the well inclination angle and drilled smoothly along sweet spot 1. The on-site oil and gas indications were then fed back to the design team. After discussion, it was decided to abandon sweet spot 1 and change the drilling objective to evaluate the oil and gas conditions of sweet spot 2 in shale oil. The well trajectory was then re-optimized, as detailed below. Figure 6 As shown.

[0145] The predicted vertical height difference between sweet spot section 1 and sweet spot section 2 is 15 meters. Based on the relationship between the well inclination angle and the formation dip angle, it is estimated that the drill bit will enter sweet spot section 2 after drilling another 80 meters after exiting sweet spot section 1. Calculations show that the theoretical drilling time for the formation in sweet spot section 1 is 6-9 min / m. After the drill bit exits sweet spot section 1, it enters a partition layer dominated by clayey mixed shale. The formation brittleness index decreases, drillability is poor, and drilling time increases. A drilling time greater than 9 min / m is used as the criterion for exiting sweet spot section 1.

[0146] At a depth of 3605 meters, the drilling time reached 9.3 min / m. After circulating the cuttings back to the surface, the lithology at the drill bit's location was determined to be clayey mixed shale, indicating entry into the partition layer. In two well sections, lithology and rock pyrolysis parameters were collected and logged at 3605-3615 meters and 363-3640 meters, respectively. The theoretical drilling time for the formation in the 3605-3615 meter section was calculated to be 8-14 min / m, and for the 363-3640 meter section, it was 7-13 min / m. Using the drilling time of 7-13 min / m as the theoretical drilling time between sweet spot section 1 and sweet spot section 2, it was predicted that the drilling time would decrease after the drill bit entered sweet spot section 2 due to changes in lithology and oil content.

[0147] When drilling reached a depth of 3685 meters, the drilling time suddenly dropped from 8.3 min / m to 4 min / m. A drilling pause was immediately initiated, a circulation was set, and waiting was conducted for cuttings and gas logging data to determine the downhole oil and gas grade. Field logging data showed that the cuttings contained 19.25% felsic minerals, 70.25% carbonate minerals (66% dolomite, 8.5% calcite), and 8.75% clay minerals, classifying the rock as gray argillaceous dolomite. Field measurements showed a TOC of 0.76%, equivalent to an oil content of 454.95%, a correlation grade of 8.6, an oil saturation index of 329.33 mg / g TOC, and a total hydrocarbon value of 100%. Based on the comprehensive oil and gas indications, this sweet spot was determined to be a Class I oil-bearing layer. This marked the second successful entry into the window of the horizontal well. This method provides accurate evaluation results after only 0.2 meters of actual penetration, ensuring the well trajectory remains within the upper-middle part of the sweet spot box, reducing the risk of encountering the layer, and enabling efficient and rapid drilling under stable well inclination conditions.

[0148] Furthermore, the present invention also includes a system for implementing a method for real-time evaluation of shale oil drilling sweet spots, such as... Figure 7 As shown, it includes a comprehensive module, a quantitative module, an analysis module, a first calculation module, and a second calculation module. Each module corresponds to the real-time evaluation method for shale oil drilling sweet spots, as detailed below:

[0149] The integrated module is used to establish the first drilling time model based on parameters such as drill bit wear coefficient, drilling pressure, rotation speed, drilling fluid properties, formation brittleness, and oil content.

[0150] The quantitative module is used to quantify the drill bit wear coefficient in the first drilling time model, stabilize the drilling pressure, rotation speed and drilling fluid performance conditions, obtain the mathematical relationship between drilling time and formation brittleness and oil content, and establish the second drilling time model.

[0151] The analysis module is used to obtain the theoretical values ​​of the drilling time before and after the drill bit enters the window based on the second drilling time model;

[0152] The first calculation module is used to calculate the theoretical value before drilling into the window and adjust the drill bit position until the window is entered.

[0153] The second calculation module is used to perform drilling after entering the window based on the theoretical value of drilling time after entering the window, and to adjust the drill bit position.

[0154] The first calculation module includes a first collection unit, an analysis unit, a construction unit, and a first adjustment unit. Each unit corresponds to the method in S4, and will not be described in detail here.

[0155] The second calculation unit includes a second collection unit, a calculation unit, and a second adjustment unit. Each unit corresponds to the method in S5, and will not be described in detail here.

[0156] The shale oil drilling sweet spot real-time evaluation system of the present invention also includes a drill bit wear coefficient evaluation module, a drill pressure and rotation speed monitoring module, a drilling fluid performance evaluation module, a lithology-based impact on drilling time evaluation module, an oil content-based impact on drilling time evaluation module, a sweet spot real-time evaluation module, and a window entry and horizontal section optimized fast drilling module. The functions of each module are as follows:

[0157] The drill bit wear coefficient evaluation module is used to obtain the thickness of the drilled formation, Young's modulus parameters of the rock, and practical time data to determine the drill bit wear coefficient and the influence coefficient of the drill bit on drilling time under the wear level.

[0158] The drilling pressure and speed monitoring module is used to monitor drilling pressure and speed data in real time, monitor the changes in drilling pressure and speed, and maintain the stability of drilling pressure and speed.

[0159] The drilling fluid performance evaluation module is used to collect parameters such as drilling fluid density, viscosity, inlet flow rate, outlet flow rate, and volume change of drilling fluid in the well to determine the stability of mud performance.

[0160] The lithology-based impact on drilling time evaluation module is used to evaluate the degree of impact of lithology on drilling time;

[0161] The module for evaluating the impact of oil content on drilling time is used to collect information on oil abundance.

[0162] The real-time evaluation module for sweet spots is used to collect data such as cuttings logging and gas logging on site, establish a model of the relationship between drilling time and lithology and oil content, and use drilling time to reflect underground geological information;

[0163] The window and horizontal section fast drilling module is used for window guidance, horizontal section tracking and fast drilling in shale oil horizontal wells.

[0164] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for real-time evaluation of shale oil drilling sweet spots, characterized in that, Includes the following steps: The first drilling time model was established based on parameters such as drill bit wear coefficient, drilling pressure, rotation speed, drilling fluid properties, formation brittleness, and oil content. The drill bit wear coefficient in the first drilling time model was quantitatively determined, and the drilling pressure, rotation speed and drilling fluid performance conditions were stabilized to obtain the mathematical relationship between drilling time and formation brittleness and oil content, and to establish the second drilling time model. The theoretical values ​​of drilling time before and after the drill bit enter the window are obtained based on the second drilling time model. Drill before the window is entered based on the theoretical value of the drilling time before the window is entered, and adjust the drill bit position until the window is entered; Drilling is performed after the window is entered, based on the theoretical value of drilling time after the window is entered, and the drill bit position is adjusted. The relationship of the first drilling time model is as follows: ZS=a×(1-Ad)+b×Bp+c×Rs+d×D f +e×Li+f×Oi+z; Where ZS is drilling time, min / m; Ad is drill bit wear coefficient, dimensionless; a is the influence coefficient of drill bit on drilling time under wear conditions, min / m; Bp is drilling pressure, kN; b is the influence coefficient of drilling pressure on drilling time, min / m·kN; Rs is rotational speed, rpm; c is the influence coefficient of rotational speed on drilling time, min / m·rpm; D f denoted as drilling fluid properties, dimensionless; d is the drilling time influence coefficient of standard drilling fluid under formation conditions, min / m; Li is the formation brittleness index, dimensionless; e is the influence coefficient of formation brittleness index on drilling time, min / m; Oi is oil abundance, mg / g; f is the influence coefficient of oil abundance on drilling time, min / m·mg / g; z is the corrected drilling time, min / m. The relationship between the drilling fluid properties is as follows: ； Among them, D f The drilling fluid properties are dimensionless; Δv' is the actual change in drilling fluid volume in the well, in meters. 3 Δv is the change in drilling fluid volume, m 3 ; The relationship of the second drilling time model is as follows: ZS = e×Li + f×Oi + Z; Where ZS is the drilling time, min / m; Li is the brittleness index of the rock formation, dimensionless; e is the influence coefficient of the brittleness index of the rock formation on the drilling time, min / m; Li is the brittleness index of the rock formation, dimensionless; Oi is the oil abundance, mg / g; f is the influence coefficient of the oil abundance on the drilling time, min / m·mg / g; Z is the corrected drilling time, min / m.

2. The method for real-time evaluation of shale oil drilling sweet spots according to claim 1, characterized in that, Both the drilling pressure and rotation speed are inversely proportional to the drilling time.

3. The method for real-time evaluation of shale oil drilling sweetness according to claim 1, characterized in that, Drilling before the window is entered, based on theoretical values ​​for drilling time, and adjusting the drill bit position until the window is entered, including the following steps: Divide the drilling route 160m before the window into n segments, where n≥2. Starting from the i-th segment, select 5-10 sample points at 2-meter intervals, where n≥i≥1, and collect rock cuttings. Based on the lithology analysis of the depth corresponding to the cuttings, the cuttings are repositioned using theoretical values ​​during drilling before the entry window, and the formation brittleness index corresponding to the lithology is found. A third drilling time model was established based on the second drilling time model and the formation brittleness index; Adjust the drill bit position based on the third drilling time model until it enters the window.

4. The method for real-time evaluation of shale oil drilling sweetness according to claim 3, characterized in that, The relationship of the third drilling time model is as follows: ZS=e i ×Li i +Z i ; Where ZS is the drilling time, min / m; e i Li is the influence coefficient of the brittleness index of the i-th stratum on drilling time, in min / m; i Z is the brittleness index of the i-th rock stratum, dimensionless; i The corrected drilling time (min / m) for the i-th segment before entering the window, under controlled drilling pressure, rotation speed, and drilling fluid properties.

5. The method for real-time evaluation of shale oil drilling sweet spots according to claim 2, characterized in that, Drilling after entering the window is performed based on the theoretical values ​​for drilling time after entering the window, and the drill bit position is adjusted, including the following steps: After entering the window, the drill bit enters the sweet spot box. In the sweet spot box, 5-10 sample points are selected at 1-meter intervals to collect rock cuttings. Data on the lithology, brittleness index, and oil content of rock cuttings are obtained, and then the data are substituted into the second model to obtain the calculation results; The calculation results are compared with the theoretical values ​​for drilling after entering the window. Then the drill bit position is determined. If the drill bit is outside the dessert box, the drill bit is adjusted back to the dessert box. Otherwise, the drill bit position changes are tracked.

6. The system corresponding to the real-time evaluation method for shale oil drilling sweet spot according to any one of claims 1-5, characterized in that, It includes a comprehensive module, a quantitative module, an analysis module, a first calculation module, and a second calculation module; The integrated module is used to establish a first drilling time model based on parameters such as drill bit wear coefficient, drilling pressure, rotation speed, drilling fluid properties, formation brittleness, and oil content. The quantitative module is used to quantify the drill bit wear coefficient in the first drilling time model, stabilize the drilling pressure, rotation speed and drilling fluid performance conditions, obtain the mathematical relationship between drilling time and formation brittleness and oil content, and establish the second drilling time model. The analysis module is used to obtain the theoretical values ​​of the drilling time before and after the drill bit enters the window based on the second drilling time model. The first calculation module is used to perform pre-drilling based on theoretical values ​​during pre-drilling and to adjust the drill bit position until the window is entered. The second calculation module is used to perform drilling after entering the window based on the theoretical value of drilling after entering the window, and to adjust the drill bit position.

7. The shale oil drilling sweet spot real-time evaluation system according to claim 6, characterized in that, The first computing module includes a first collection unit, an analysis unit, a construction unit, and a first adjustment unit; The first collection unit is used to divide the drilling route 160m before the window into n segments, where n≥2. Starting from the i-th segment, 5-10 sample points are selected at 2-meter intervals, where n≥i≥1, to collect rock cuttings. The analysis unit is used to analyze lithology based on the depth of the cuttings, use theoretical values ​​from the pre-drilling window to reposition the cuttings, and find the formation brittleness index corresponding to the lithology. The building unit is used to establish a third drilling time model based on the second drilling time model and the formation brittleness index; The first adjustment unit is used to adjust the drill bit position based on the third drilling time model until it enters the window.

8. The real-time evaluation system for shale oil drilling sweet spots according to claim 6, characterized in that, The second calculation module includes a second collection unit, a calculation unit, and a second adjustment unit; The second collection unit is used to collect rock cuttings by selecting 5-10 sample points at 1-meter intervals in the sweet spot box after the drill bit enters the sweet spot box through the entry window. The calculation unit is used to acquire data on the lithology, brittleness index, and oil content of rock cuttings, and then substitute the data into the second model to obtain the calculation results. The second adjustment unit is used to compare the calculation results with the theoretical value of drilling after entering the window, and then determine the position of the drill bit. If the drill bit is outside the dessert box, the drill bit is adjusted back to the dessert box; otherwise, the drill bit position changes are tracked.

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