US 20020104685 A1 Abstract A method of and system for controlling directional drilling determines a relationship between surface drill string orientation angle and drill bit face angle. The method uses the relationship to determine a predicted drill bit face angle. The method then uses the predicted drill bit face angle to achieve a target drill bit face angle by calculating a surface drill string correction angle. The correction angle may be displayed to a human driller. Alternatively, the correction angle may be provided as an input to an automated drilling machine.
Claims(26) 1. A method of controlling directional drilling, which comprises:
determining a relationship between a first drilling control variable and drill bit face angle; determining, based upon said relationship, a target first control variable value to achieve a target face angle; and, correcting current first drilling control variable to said target first drilling control variable to achieve said target face angle. 2. The method as claimed in collecting drill bit face angle and first drilling control variable data. 3. The method as claimed in performing linear regression of said drill bit face angle and said first drilling control variable data, to obtain a mathematical model with drill bit face angle as a response variable and first drilling control variable as an explanatory variable. 4. The method as claimed in solving said mathematical model for a measured first drilling control variable value. 5. The method as claimed in calculating a surface drill string correction angle to achieve said target face angle. 6. The method as claimed in 7. The method as claimed in 8. The method as claimed in 9. The method as claimed in determining a relationship between rate of penetration and a second drilling control variable; determining a target second drilling control variable value, based upon said relationship between rate of penetration and said second drilling control variable, to achieve an optimum rate of penetration; and, maintaining said second drilling control variable at said target second drilling control variable value. 10. The method as claimed in collecting rate of penetration data. 11. The method as claimed in performing linear regression of said rate of penetration data and said second drilling control variable data, to obtain a mathematical model with rate of penetration as response variable and second drilling control variable as an explanatory variable. 12. The method as claimed in displaying said target second drilling control variable value. 13. The method as claimed in inputting said target drilling control variable value to an automatic drilling machine. 14. The method as claimed in 15. A directional drilling control system, which comprises:
means for determining a relationship between a first drilling control variable and a drill bit face angle; means for predicting, based upon said relationship, a target first drilling control variable to achieve a target drill bit face angle; and, means for determining a correction to said target first drilling control variable to achieve a target face angle. 16. The system as claimed in means for collecting drill bit face angle and first drilling control variable data. 17. The system as claimed in means for performing linear regression of said drill bit face angle and said first drilling control variable data, to obtain a mathematical model with drill bit face angle as response variable and first drilling control variable as an explanatory variable. 18. The system as claimed in means for solving said mathematical model for said first drilling control variable value. 19. The system as claimed in means for calculating a surface drill string correction angle to achieve said target face angle. 20. The system as claimed in 21. The system as claimed in means for determining a relationship between rate of penetration and a second drilling control variable; means for determining a target control variable value, based upon said relationship between rate of penetration and said second drilling control variable, to achieve an optimum rate of penetration. 22. The system as claimed in means for collecting rate of penetration data. 23. The system as claimed in means for performing linear regression of said rate of penetration data and said second drilling control variable data, to obtain a mathematical model with rate of penetration as response variable and second drilling control variable as an explanatory variable. 24. The system as claimed in a display for displaying said target second drilling control variable value. 25. The system as claimed in an automatic drilling machine arranged to receive said target control variable value. 26. A method of drilling, which comprises:
determining a relationship between surface drill string angular orientation and drill bit face angle; determining, based upon said relationship, a target surface drill string angular orientation to achieve a target face angle; correcting current surface drill string angular orientation to said target surface drill string angular orientation to achieve said target face angle; determining a relationship between rate of penetration and a drilling control variable; determining a target drilling control variable value, based upon said relationship between rate of penetration and said drilling control variable, to achieve an optimum rate of penetration; and, maintaining said drilling control variable at said target second drilling control variable value. Description [0001] The present application claims the benefit of U.S. Provisional Application No. 60/252,752, filed Nov. 21, 2000, titled Method of and System for Controlling Directional Drilling. [0002] The present invention relates generally to the field of oil and gas well drilling. More particularly, the present invention relates to a method of and system for controlling directional drilling. [0003] It is very expensive to drill bore holes in the earth such as those made in connection with oil and gas wells. Oil and gas bearing formations are typically located thousands of feet below the surface of the earth. Accordingly, thousands of feet of rock must be drilled through in order to reach the producing formations. Additionally, many wells are drilled directionally, wherein the target formations may be spaced laterally thousands of feet from the well's surface location. Thus, in directional drilling, not only must the depth but also the lateral distance of rock must be penetrated. [0004] The cost of drilling a well is primarily time dependent. Accordingly, the faster the desired penetration location, both in terms of depth and lateral location, is achieved, the lower the cost in completing the well. [0005] While many operations are required to drill and complete a well, perhaps the most important is the actual drilling of the bore hole. In order to achieve the optimum time of completion of a well, it is necessary to drill at the optimum rate of penetration and to drill in the minimum practical distance to the target location. Rate of penetration depends on many factors, but a primary factor is weight on bit. In mud motor bent sub directional drilling, the best indication of weight on bit is mud motor differential pressure. [0006] As disclosed, for example in Millheim, et al., U.S. Pat. No. 4,535,972, rate of penetration increases with increasing weight on bit until a certain weight on bit is reached and then decreases with further weight on bit. Thus, there is generally a particular weight on bit that will achieve a maximum rate of penetration. [0007] Drill bit manufacturers provide information with their bits on the recommended optimum weight on bit. However, the rate of penetration depends on many factors in addition to weight on bit. For example, the rate of penetration depends upon characteristics of the formation being drilled, the speed of rotation of the drill bit, and the rate of flow of the drilling fluid. Because of the complex nature of drilling, a weight on bit that is optimum for one set of conditions may not be optimum for another set of conditions. [0008] Directional drilling has been a combination of art and skill as well as science and engineering. The direction of drilling is determined by the azimuth or face angle of the drilling bit. Face angle information is measured downhole by a steering tool. Face angle information is typically conveyed from the steering tool to the surface using relatively low bandwidth mud pulse signaling. The driller attempts to maintain the proper face angle by applying torque corrections to the drill string. However, because of the latency in receiving face angle information, the driller typically over- or under-corrects. The over- or under-correction results in substantial back and forth wandering of the drill bit, which increases the distance that must be drilled in order to reach the target formation. Back and forth wandering also increases the risk of stuck pipe and makes the running and setting of casing more difficult. [0009] The present invention provides a method of and system for controlling directional drilling by determining a relationship between a first drilling control variable and drill bit face angle. The method and system of the present invention use the relationship to determine a predicted drill bit face angle. The method and system then use the predicted drill bit face angle to achieve a target drill bit face angle by calculating a surface drill string correction angle. The correction angle may be displayed to a human driller. Alternatively, the correction angle may be provided as an input to an automated drilling machine. [0010] The method and system of the present invention determine the relationship between the first drilling control variable and the drill bit face angle by collecting drill bit face angle and control variable data. The method and system periodically perform linear regression of the drill bit face angle and first drilling control variable data, to obtain a mathematical model with drill bit face angle as response variable and first drilling control variable as an explanatory variable. The method and system determine the predicted drill bit face angle by solving the mathematical model for a measured first drilling control variable value. [0011] The method and system of the present invention also optimize rate of penetration. The method and system determine a relationship between rate of penetration and a second drilling control variable. The method and system determine a target second drilling control variable value, based upon the relationship between rate of penetration and the second drilling control variable. A driller maintains the control variable at the target control variable value. As in the case of the correction angle, the target second drilling control variable may be displayed to a human driller or inputted to an automated drilling machine. [0012]FIG. 1 is a pictorial view of a directional drilling system. [0013]FIG. 2 is a block diagram of a directional driller control system according to the present invention. [0014]FIG. 3 is a pictorial view of a display screen according to the present invention. [0015]FIG. 4 is a flowchart of data collection and generation according to the present invention. [0016]FIG. 5 is a flowchart of display processing according to the present invention. [0017] FIGS. [0018]FIG. 7 is a flowchart of face angle processing according to the present invention. [0019] Referring now to the drawings and first to FIG. 1, a drilling rig is designated generally by the numeral [0020] Rig [0021] Drill string [0022] A bent sub mud motor drilling tool [0023] Referring now to FIG. 2, there is shown a block diagram of a preferred system of the present invention. The system includes a mud pump pressure sensor [0024] Referring still to FIG. 2, the system of the present invention includes a hook speed/position sensor [0025] The system of the present invention includes a steering tool [0026] The system of the present invention also includes a drill string angle sensor [0027] In FIG. 2, the digital outputs of sensors [0028] Referring now to FIG. 3, a display screen according to the present invention is designated by the numeral [0029] As will be explained in detail hereinafter, the method and system of the present invention constructs a mathematical model of the relationship between Delta_P and rate of penetration for the current drilling environment. The mathematical model is built from data obtained from pump pressure sensor [0030] According to one aspect of the present invention, a driller attempts to match the value displayed in current Delta_P display [0031] Display screen [0032] Display screen [0033] Display screen [0034] Referring now to FIGS. [0035] Referring now to FIG. 5, there is shown display processing according to the present invention. The system displays the current average Delta_P, which is calculated at block [0036] Referring now to FIG. 6, and particularly to FIG. 6A, there is shown a flow chart of the building of a drilling model and calculation of target rate of penetration and Delta_P according to the present invention. In the preferred embodiment, FIG. 6 processing is performed once every five seconds. First, the system cleans the data stored according to FIG. 4 processing and populates a data array, at block [0037] The clean data are stored in a data array. The data array includes an index column, a Delta_P column, and an ROP column. The data array also includes a first lagged ROP column and a second lagged ROP column. The first lagged ROP is denoted ROP(t- [0038] After populating the data array with clean data, at block [0039] where α is the intercept, β [0040] After the system has performed multilinear regression at block [0041] Referring to FIG. 6E, the system tests, at decision block [0042] Referring now to FIG. 6C, after determining target Delta_P, the system calculates a target rate of penetration based upon the target Delta_P and the model of equation (1), at block [0043] After completing steps [0044] Referring now to FIG. 7, there is shown a flow chart of face angle processing according to the present invention. A target face angle is determined according to directional drilling plan to achieve the desired path through the earth to reach a target location. The target face angle may be periodically recalculated. The system of the present invention cleans the face angle and drill string orientation data and populates a data array, at block Face_Angle( [0045] where σ is the intercept, μ [0046] Alternatively, the system may forecast a face angle based upon an Exponentially Weighted Moving Average (EWMA) or Box-Jenkins technique. As is well known to those skilled in the art, EWMA is a statistic for monitoring a process that averages the data in a way that gives less and less weight to data as they are further removed in time. The EWMA statistic is calculated as follows: [0047] where Y(t) is the observed value at time t, and λ is a weighting constant having a value greater than zero and equal to or less than one. The weighting constant λ determines the rate at which older data enter into the calculation of the EWMA statistic. A λ value close to one gives more weight to recent data and less weight to older data. Similarly, a λ value close to zero gives more weight to older data and less weight to recent data. Usually a λ value between 0.2 and 0.3 yields a good balance between more recent and less recent data. [0048] After the system has determined the relationship between drill string orientation and face angle, the system calculates an angular correction necessary to achieve the target face angle, at block [0049] According to the present invention, angular correction is expressed as the difference between the current drill string orientation and the target drill string orientation calculated by Equation (4). After calculating the angular correction at block [0050] From the foregoing, it may be seen that the present invention is well adapted to overcome the shortcomings of the prior art. The system of the present invention builds mathematical models of the relationships between Delta_P and rate of penetration as well as drill string orientation and face angle, for the current drilling environment. The system continuously updates the mathematical models to reflect changes in the drilling environment. The system of the present invention enables a driller to optimize rate of penetration and control the direction of drilling simultaneously. Referenced by
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