A correction method for the modified weight-on-bit index based on mechanical efficiency evaluation

Abstract

The present invention discloses a correction method for the modified bit weight index based on mechanical efficiency evaluation, comprising the following steps: Step 1, collect various engineering parameters according to the sampling period; Step 2, calculate the mechanical specific energy of the drilled section and establish a baseline of rock compressive strength; Step 3, obtain the mechanical efficiency based on the mechanical specific energy and the baseline of rock compressive strength, and obtain the corrected modified bit weight index. The method provided by the present invention corrects the modified bit weight index by calculating the mechanical specific energy of the drilled section and the baseline of rock compressive strength according to the comprehensive logging data, and finally improves the application effect of the modified bit weight index under complex working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas drilling, and more specifically, the present invention relates to a correction method for a modified weight-on-bit index based on mechanical efficiency evaluation. Background Art

[0002] The modified weight-on-bit index, also known as the d c index, is the most commonly used calculation parameter in the current real-time formation pressure monitoring during drilling. The d c index has gone through two main stages:

[0003] In the first stage, Bingham proposed the Bingham drilling rate equation in 1965: Under the condition of temporarily not considering the influence of other factors such as hydraulics, the mechanical drilling rate of the bit can be calculated from a series of drilling engineering parameters, and the d index was proposed. After statistically analyzing a large amount of actual drilling data in the Gulf of Mexico, Jorden and Shirley found the nearly linear relationship between the d index and the bottom hole pressure difference, that is, as the bottom hole pressure difference decreases, the d index becomes smaller. Therefore, the change of the d index can be used to judge the occurrence of abnormal formation high pressure, but the specific magnitude of the abnormal formation high pressure cannot be calculated yet.

[0004] In the second stage, in order to eliminate the influence of drilling fluid density on the d index, Rehm and McClendon proposed the modified d index, that is, the d c index in 1971. In a formation with normal pressure, as the depth increases, the degree of shale compaction increases, the mechanical drilling rate decreases, and the d c index increases. According to the shale point data in the normal formation pressure section, a trend line of the d c index changing with depth under normal formation pressure conditions can be statistically analyzed or plotted, which is called the normal trend line. In the section with abnormal formation pressure, the amplitude of the d c index deviating from the normal trend line has a positive correlation with the amplitude of the formation pressure anomaly. According to the response characteristics of the d c index to abnormal pressure, Eaton proposed the Eaton formula for calculating the formation pressure coefficient based on the d c index in 1975.

[0005] The d c index and the Eaton method have solved the problem of formation pressure quantification. And because the d c index can be calculated in real time through the engineering parameters of the drilling in progress, the technical combination of the d c index and the Eaton method has been widely used at home and abroad. However, in practical applications, the limitations of the d c index itself have greatly affected the real-time formation pressure monitoring effect, which is mainly reflected in the following two aspects:

[0006] 1. When the drilling engineering conditions change, such as tripping in and out to replace the bit, or the bit diameter becomes smaller, etc., c the normal trend line of the d-exponent needs to be translated in the semi-logarithmic coordinate system. The translation accuracy is limited by the formation characteristics and the complexity of the drilling operation, and the experience level of the operator also has a great influence on the effect of the translation process.

[0007] 2. As the bit wears continuously during the process of drilling in the formation, the rock-breaking efficiency of the bit gradually decreases. When the bit wear reaches a certain level, the drilling time increases rapidly, c the d-exponent shows an abnormally large value, and at this time c the d-exponent has lost its significance for formation pressure monitoring.

[0008] It should be emphasized that abnormally high formation pressure usually develops in geological bodies with characteristics such as deep layers and deep water. Due to the continuous increase in well depth and multiple casing layers, the complexity of the drilling operation continuously rises, specifically manifested as unclean bottom hole and fast bit wear. Therefore, in the abnormal formation pressure monitoring work under the complex working conditions of high-pressure wells, c the monitoring effect of the d-exponent is greatly restricted. Summary of the Invention

[0009] The present invention designs and develops a correction method for the modified drilling pressure index based on mechanical efficiency evaluation, which overcomes the defects of the prior art. According to the comprehensive mud logging data, by calculating the mechanical specific energy and the rock compressive strength baseline of the drilled section, the modified drilling pressure index is corrected, and finally the application effect of the modified drilling pressure index under complex working conditions is improved.

[0010] The technical solution provided by the present invention is as follows:

[0011] A correction method for the modified drilling pressure index based on mechanical efficiency evaluation, comprising the following steps:

[0012] Step 1: Collect various engineering parameters according to the sampling period;

[0013] Step 2: Calculate the mechanical specific energy of the drilled section and establish the rock compressive strength baseline;

[0014] Step 3: Obtain the mechanical efficiency according to the mechanical specific energy and the rock compressive strength baseline, and obtain the corrected modified drilling pressure index:

[0015]

[0016] wherein, cc is the corrected modified drilling pressure index, R is the drilling speed, N is the rotary table speed, F is the mechanical efficiency, W is the drilling pressure, D b is the bit diameter, ρ n is the formation water density, ρm is the density of the drilling fluid.

[0017] Preferably, the multiple engineering parameters include weight on bit, penetration rate, drilling speed, bit diameter, density of the drilling fluid, rotary speed of the rotary table, and torque.

[0018] Preferably, the sampling period is 1 m.

[0019] Preferably, step two specifically includes the following steps:

[0020] Step 1: Calculate the mechanical specific energy of the drilled section and obtain the mechanical specific energy curve of the normal pressure section;

[0021] Step 2: Establish a semi-logarithmic coordinate system with well depth and mechanical specific energy as the horizontal and vertical coordinates;

[0022] Step 3: Select two normal pressure points on the mechanical specific energy curve, use the projection points of the two normal pressure points on the semi-logarithmic coordinate system as control points, and establish a trend line passing through the control points as the rock compressive strength baseline.

[0023] Preferably, the mechanical specific energy satisfies:

[0024]

[0025] In the formula, MSE is the mechanical specific energy, and T is the torque of the bit.

[0026] Preferably, the selection of the two normal pressure points satisfies:

[0027] The distance between the two normal pressure points is greater than 300 m, the fluctuations of the penetration rate values and mechanical specific energy values within 5 m before and after the two normal pressure points do not exceed 10%, and both of the two normal pressure points are in the middle-upper formation or the normal pressure section.

[0028] Preferably, the mechanical efficiency satisfies:

[0029] F = MSE / CCS;

[0030] In the formula, CCS is the rock compressive strength baseline value.

[0031] Preferably, the torque of the bit satisfies:

[0032]

[0033] In the formula, T is the torque of the bit, ξ is the safety factor, K is the drilling fluid adhesion constant, P S is the fluctuating pressure, P f is the bit pressure drop, D v is the equivalent diameter of the nozzle, and H is the well depth.

[0034] Advantages of the present invention:

[0035] The method for correcting the modified bit weight index based on mechanical efficiency evaluation provided by the present invention calculates the mechanical specific energy of the drilled section, uses the mechanical specific energy curve of normal drilling in the normal pressure section as the rock compressive strength baseline, and then evaluates the mechanical efficiency of the bit according to the ratio of the rock compressive strength baseline to the mechanical specific energy, so as to correct the modified bit weight index, and finally improve the application effect of the modified bit weight index under complex working conditions, and can improve the accuracy and reliability of formation pressure while-drilling monitoring from the data source. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic flow chart of the method for correcting the modified bit weight index based on mechanical efficiency evaluation according to the present invention.

[0037] Figure 2 It is a result comparison chart of calculating formation pressure according to different parameters in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The following further describes the present invention in detail with reference to the drawings, so that those skilled in the art can implement it according to the description in the specification.

[0039] As Figure 1 shown, the present invention provides a method for correcting the modified bit weight index based on mechanical efficiency evaluation. As Figure 1 shown, it includes the following steps:

[0040] Step 1. According to the sampling period, collect and record various engineering parameters through a comprehensive logging tool, including bit weight, penetration rate, drilling speed, bit diameter, drilling fluid density, rotary speed, and torque parameters;

[0041] Among them, the sampling period is 1 m, that is, a set of the above engineering parameters is collected every 1 m of formation drilled by the bit;

[0042] Step 2. Calculate the mechanical specific energy of the drilled section and establish a rock compressive strength baseline;

[0043] Specifically, Step 2 includes the following steps:

[0044] Step 1. Calculate the mechanical specific energy of the drilled section and obtain the mechanical specific energy curve of the normal pressure section;

[0045] Among them, the mechanical specific energy satisfies:

[0046]

[0047] In the formula, MSE is the mechanical specific energy, with the unit of megapascal; T is the torque of the bit, with the unit of kilonewton / meter.

[0048] Among them, the torque of the drill bit satisfies:

[0049]

[0050] In the formula, T is the torque of the drill bit, ξ is the safety factor, K is the drilling fluid adhesion constant, P S is the fluctuating pressure, P f is the drill bit pressure drop, D v is the equivalent diameter of the nozzle, H is the well depth;

[0051] The value range of the safety factor is 0.01 - 0.9, and the value range of the drilling fluid adhesion constant is 0.45 - 0.5;

[0052] Step 2: Establish a semi-logarithmic coordinate system with well depth and mechanical specific energy as the horizontal and vertical coordinates;

[0053] Step 3: Select two normal pressure points on the mechanical specific energy curve, use the projection points of the two normal pressure points on the semi-logarithmic coordinate system as control points, and establish a trend line passing through the control points as the rock compressive strength baseline;

[0054] Among them, the selection of the two normal pressure points satisfies:

[0055] The distance between the two normal pressure points is greater than 300m, the fluctuations of the drilling time values and mechanical specific energy values within 5m before and after the two normal pressure points do not exceed 10%, and the two normal pressure points are both in the middle-upper formation or normal pressure section.

[0056] Step three: Obtain the mechanical efficiency according to the mechanical specific energy and the rock compressive strength baseline, and obtain the corrected modified bit weight index:

[0057]

[0058] In the formula, d cc is the corrected modified bit weight index, dimensionless; R is the drilling rate, unit is m / h; N is the rotary table speed, unit is r / min; F is the mechanical efficiency, dimensionless; W is the bit weight, unit is kN; D b is the bit diameter, unit is mm, ρ n is the formation water density, unit is g / cm 3 ; ρ m is the drilling fluid density, unit is g / cm 3 .

[0059] Among them, the mechanical efficiency satisfies:

[0060] F = MSE / CCS;

[0061] In the formula, CCS is the rock compressive strength baseline value, unit is MPa.

[0062] After obtaining the corrected modified weight-on-bit index according to the present invention, referring to the Eaton method in Part 3 of the Petroleum and Natural Gas Industry Standard of the People's Republic of China "SYT5623-2009 - Formation Pressure Prediction (Monitoring) Method", the formation pressure coefficient is calculated.

[0063] The present invention makes full use of the drilling engineering data on the oil and gas drilling site, and can correct the modified weight-on-bit index during the actual drilling process, thereby improving the application effect of the modified weight-on-bit index and providing help for the accurate calculation of the formation pressure while drilling.

[0064] Example 1

[0065] The present invention has been applied in the formation pressure monitoring while drilling of 5 wells in the Pearl River Mouth Basin. Under the complex drilling conditions with complex wellbore structures and multiple premature bit replacements, the modified weight-on-bit index has been effectively corrected. Using the cc formation pressure coefficient calculated by the Eaton method with the d c index reaches a compliance rate of 95%, and is 15% higher compared with the calculation result of the commonly used d

[0066] The application in the Pearl River Mouth Basin shows that the method of calculating the formation pressure by combining the corrected modified weight-on-bit index with the Eaton method has good calculation accuracy under the conditions of unclear formation pressure distribution and complex drilling conditions. This method is not affected by differences such as geological background and changes in drilling conditions. It can also timely and accurately identify and judge the abnormal formation high pressure encountered during the drilling operation in the exploration of new exploration areas and new formation systems. This application effect has successfully improved the formation pressure monitoring accuracy while drilling in this area and meets the engineering requirements for ensuring drilling safety and protecting oil and gas reservoirs.

[0067] The present invention collects the real-time logging data while drilling, calculates the mechanical specific energy of the drilled section, takes the mechanical specific energy curve of normal drilling in the normal pressure section as the rock compressive strength baseline, and then evaluates the mechanical efficiency of the bit work according to the ratio of the rock compressive strength baseline to the mechanical specific energy, corrects the modified weight-on-bit index, thereby improving the application effect of the modified weight-on-bit index under complex working conditions, and can improve the accuracy and reliability of the formation pressure monitoring while drilling from the data source.

[0068] Example 2

[0069] Taking Well A as an example, this well is deployed on the northern slope of the main depression of the Baiyun Sag in the Pearl River Mouth Basin. Abnormal formation high pressure develops in the main target formations Zhuhai Formation and Enping Formation. By collecting the real-time logging data while drilling of this well, an integrated engineering logging chart (as Figure 2 shown) is established. Due to the reason of tripping to replace the bit, the d cThe exponent fluctuates violently after entering 3000m. In this well, when applying d c to evaluate formation pressure with the exponent, it is necessary to offset d c the exponent trend line 4 times. In the interval from the shallow layer to 3200m, d c the exponent changes along the normal trend line, and it is judged that this section is a normal pressure formation. Based on this, 2 normal pressure points are selected on the mechanical specific energy curve (MSE) in the well section of 2000m - 3200m, the rock compressive strength baseline (CCS) is drawn, and the d cc exponent curve changing with well depth is obtained. As Figure 2 shown, d cc the exponent is not affected by stopping drilling to replace the bit, and there is no significant overall offset. After entering 3200m, d c the exponent and d cc the exponent both deviate from the normal trend line, indicating that abnormal high pressure has been encountered. Finally, the formation pressure is calculated respectively using the Eaton method in combination with d c the exponent and d cc the exponent.

[0070] Referring to the pressure measurement results obtained by the modular formation dynamics tester (MDT) after the well is drilled, as well as the formation pressure calculation results calibrated by the sonic method through pressure measurement data, the formation pressure results calculated by d c the exponent and d cc the exponent are compared. The results show that the deviation amplitude of d cc the exponent from the normal compaction trend line corresponds well to the formation pressure coefficient, and the formation pressure coefficient calculated by the Eaton method based on d cc the exponent is in good agreement with the pressure measurement results, and the coincidence rate of the two reaches 95%. It is more accurate than the calculation result using the Eaton method based on d c the exponent.

[0071] The modified bit weight exponent correction method based on mechanical efficiency evaluation provided by the present invention, aiming at the current technical status that the formation pressure monitoring parameters while drilling are seriously affected by drilling conditions, can be used to calculate the modified bit weight exponent of the drilled formation in real time through drilling engineering parameters during drilling, so as to provide key parameters for core problems in oil and gas exploration such as reservoir identification and formation pressure evaluation.

[0072] Although the implementation embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated and described examples here.

Claims

1. A corrected bit weight index correction method based on mechanical efficiency evaluation, characterized in that It includes the following steps: Step 1: Collect various engineering parameters according to the sampling period; Step 2: Calculate the mechanical specific energy of the drilled section and establish a baseline of rock compressive strength; Step 3: Obtain the mechanical efficiency based on the mechanical specific energy and the baseline of rock compressive strength, and get the corrected modified weight-on-bit index: Where d cc is the corrected modified weight on bit index, R is the penetration rate, N is the rotary speed, F is the mechanical efficiency, W is the weight on bit, D b is the bit diameter, ρ n is the formation water density, ρ m is the drilling fluid density; The mechanical efficiency satisfies: F = MSE / CCS; In the formula, CCS is the baseline value of rock compressive strength; The mechanical specific energy satisfies: In the formula, MSE is the mechanical specific energy, and T is the torque of the bit; The torque of the bit satisfies: Where T is the torque of the drill bit, ξ is the safety factor, K is the drilling fluid adhesion constant, P S is the fluctuating pressure, P f is the drill bit pressure drop, D v is the equivalent diameter of the nozzle, and H is the well depth.

2. The method for correcting the modified weight-on-bit index based on mechanical efficiency evaluation according to claim 1, wherein The various engineering parameters include weight on bit, penetration rate, rotary speed, bit diameter, mud density, rotary table speed and torque.

3. The correction method for the modified WOB index based on mechanical efficiency evaluation according to claim 2, wherein The sampling period is 1 m.

4. The method for correcting the modified WOB index based on mechanical efficiency evaluation according to claim 1, wherein, Step 2 specifically includes the following steps: Step 1: Calculate the mechanical specific energy of the drilled section and obtain the mechanical specific energy curve of the normal pressure section; Step 2: Establish a semi-logarithmic coordinate system with well depth and mechanical specific energy as the horizontal and vertical coordinates; Step 3: Select two normal pressure points on the mechanical specific energy curve, use the projections of the two normal pressure points on the semi-logarithmic coordinate system as control points, and establish a trend line passing through the control points as the baseline of rock compressive strength.

5. The method for correcting the bit weight index based on mechanical efficiency evaluation according to claim 4, wherein The selection of the two normal pressure points satisfies: The distance between the two normal pressure points is greater than 300 m, the fluctuations of the penetration rate values and mechanical specific energy values within 5 m before and after the two normal pressure points do not exceed 10%, and both of the two normal pressure points are in the upper-middle formation or the normal pressure section.

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