IFR1 survey methodology

Abstract

An improved in-field referencing 1 (IFR1) technique is provided, wherein a single mid-lateral well measurement of local magnetic field is used. In one aspect of directional drilling, a single set of IFR values for a planned well is obtained. The single set of IFR values is captured at a single location in a mid-lateral section of the planned well. A global magnetic model corresponding to the Earth's magnetic field is obtained. An improved magnetic model is generated by correcting the global magnetic model for local anomalies using the single set of IFR values.

Claims

1. A method of directional drilling, the method comprising: obtaining a single set of in-field referencing (IFR) values for a planned well, the single set of IFR values captured by measuring local geomagnetic field data at a single location in a mid-lateral section of the planned well; generating an improved magnetic model by combining the single set of IFR values with a global magnetic model; obtaining downhole magnetic field data, the downhole magnetic field data captured along a borehole using surveying instrumentation, the borehole being drilled for the planned well; and determining an orientation of the borehole based on the downhole magnetic field data and the improved magnetic model.

2. The method of claim 1, wherein the local magnetic field data includes a local magnetic declination.

3. The method of claim 2, wherein the local magnetic field data further includes a magnetic inclination and a magnetic field strength.

4. The method of claim 2, wherein an axial interference in a short collar correction is estimated using the magnetic inclination and the magnetic field strength.

5. The method of claim 2, wherein a lateral error in an estimate of a position of the borehole is reduced using the local magnetic declination.

6. The method of claim 1, wherein the local geometric field data is measured using aeromagnetic surveying.

7. The method of claim 1, wherein determining the orientation of the borehole includes determining an azimuthal orientation of a tool axis along the borehole relative to magnetic north.

8. The method of claim 1, wherein a steerable drilling bit is steered based on the orientation of the borehole.

9. The method of claim 1, wherein a pathway of the borehole is determined using the improved magnetic model.

10. The method of claim 1, wherein a pathway for each of one or more existing lateral wells is determined using the improved magnetic model, a preplanned path being determined for a second borehole based on the pathways for the one or more existing lateral wells.

11. The method of claim 1, wherein the improved magnetic model is used in connection with at least one of: wellbore clearance, wellbore avoidance, wellbore intercept, or remote operations.

12. The method of claim 1, wherein the downhole magnetic field data is captured at a plurality of locations along the borehole.

13. A method of directional drilling, the method comprising: identifying a planned wellbore pathway, the planned wellbore pathway having a middle area of a lateral section; obtaining a single set of in-field referencing (IFR) values for the planned wellbore pathway, the single set of IFR values captured at a single location in the middle area of the lateral section; obtaining a global magnetic model corresponding to the Earth's magnetic field; generating an improved magnetic model by correcting the global magnetic model for local anomalies using the single set of IFR values; and optimizing the planned wellbore pathway using the improved magnetic model.

14. The method of claim 13, wherein a wellbore is directionally drilled according to the planned wellbore pathway optimized using the improved magnetic model.

15. The method of claim 13, wherein the single set of IFR values includes at least one of a local magnetic declination, a magnetic inclination, and a magnetic field strength.

16. The method of claim 13, wherein a steerable drilling bit is steered based on the planned wellbore pathway optimized using the improved magnetic model.

17. A method of directional drilling, the method comprising: obtaining a single set of in-field referencing (IFR) values for a planned well, the single set of IFR values captured at a single location in a mid-lateral section of the planned well; obtaining a global magnetic model corresponding to the Earth's magnetic field; generating an improved magnetic model by correcting the global magnetic model for local anomalies using the single set of IFR values; and generating a directional drilling plan based on the improved magnetic model.

18. The method of claim 17, wherein generating the directional drilling plan includes determining an orientation of a borehole based on downhole magnetic field data and the improved magnetic model, the borehole being drilled for the planned well.

19. The method of claim 18, wherein the downhole magnetic field data is captured at one or more locations along the borehole.

20. The method of claim 17, wherein the directional drilling plan includes at least one of: wellbore clearance, wellbore avoidance, wellbore intercept, or remote operations.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A-D. Prior art IFR1 methods. FIG. 1A using a single measurement taken at the wellhead. FIG. 1B using a point for each section of well. FIG. 1C. Using a single measurement at the bottom hole assembly. FIG. 1D using a multiplicity of point measurements taken along the entire well length.

(2) FIG. 2. Inventive method using a single mid-lateral point of measurement for IFR.

(3) FIG. 3. Geomagnetic models, from Buchanan (2013).

(4) FIG. 4. Magnetic field orientation, from Buchanan (2013).

DETAILED DESCRIPTION OF THE DISCLOSURE

(5) The disclosure provides a novel method of well ranging using a modified IFR1 approach, wherein a single, mid-lateral well measurement of local magnetic field is taken and used in the subsequent calculations. This method provides accurate results, yet is quick and easy, consistent with current work flow.

(6) Smaller positional uncertainty of horizontal wells reduces the danger of collisions, leads to better well placement and improves production from the reservoir. One of the largest sources of error in directional drilling is the use of inaccurate reference values for the geomagnetic field. This source of error can be reduced significantly by using an In-Field Referencing (IFR1) model derived from e.g., aeromagnetic measurements.

(7) We performed a study of existing, premapped wells to provide proof of concept herein. The purpose was to study the impact of IFR1 on wellbore position accuracy. A sample of 12 wells was selected from the Bakken Field. Ellipses of uncertainty (EOU) for standard MWD were compared with EOUs for post-processing using axial corrections, IFR, multi-station analysis and tool sag. For a typical Bakken well, these advanced techniques reduced the lateral uncertainty in the wellbore position by 43% and the vertical uncertainty by 38%.

(8) The wellbore position at total depth (TD) was then recomputed by replacing the geomagnetic declination with the more accurate local IFR1 values taken along the entire lateral well path. This shifted the lateral position of the well at TD by up to 94 ft.

(9) In order to avoid complexity in the IFR work flow, it was further investigated whether a single reference declination could be used for the entire well. Using the IFR declination at the wellhead creates a lateral error of up to 26 ft. If the declination is instead taken at the center of the lateral section (a mid-lateral declination), this error is reduced to a negligible 1.3 ft maximum error at TD.

(10) The preceding investigation shows that taking the IFR1 value at the center of the lateral section results in an almost equivalent well trajectory to using the actual IFR1 value for every survey location along the well path. For the selected wells, the maximum difference in the location at TD was 1.3 feet. The maximum deviation of the actual IFR1 values from the mean IFR1 value at the center of the lateral was found to be 19.4 nT for the total field, 0.03 for the dip and 0.03 for the declination. These are very small deviations. It was therefore concluded that only a single set of reference values needs to be used, namely the IFR values at about the center of the lateral section.

(11) Using a single mid-lateral reference value for IFR1 is beneficial because considerably less measuring need occur, and the method fits easily into current workflow with little modification. It is considerably less work intensive than measuring declination over several points along the entire well length, and less compute intensive. Yet surprisingly, the results were comparable to more extensively analyzed methods.

Test 1: Lateral Uncertainty

(12) Advanced processing reduces the uncertainty of the position of the wellbore. The following processing methods were compared in terms of their effect on ellipses of uncertainty (EOU):

(13) MWD: Standard Measurement While Drilling without post processing

(14) +AX: With axial interference correction for the magnetization of the drill string. This improves mostly the lateral position.

(15) +IFR1: Using more accurate geomagnetic reference values from an IFR crustal magnetic model, again improving mostly the lateral position.

(16) +MS: Multi-station analysis estimates accelerometer and magnetometer biases, scale factors and axial interference (essentially the bz bias) in a single inversion using all of the surveys of a tool run. This replaces the axial correction and improves both the lateral and vertical position.

(17) +SAG: Correction for the mis-alignment of the tool axis with the axis of the wellbore. This improves only the vertical position.

(18) TABLE-US-00002 TABLE 1 Lateral Uncertainty MWD + MWD + IFR1 + Lateral MWD + MWD + AX + SAG + Length MWD AX IFR1 IFR1 MS (ft) Oriented (ft) (ft) (ft) (ft) (ft) Well #1 9976 S 226 205 167 134 132 Well #2 9919 N 223 202 165 131 126 Well #3 10990 S 245 224 180 145 143 Well #4 10082 N 223 203 162 130 127 Well #5 10135 S 229 208 171 137 136 Well #6 11707 N 253 233 182 148 142 Well #7 10045 S 222 202 162 130 129 Well #8 11093 S 250 227 185 148 145 Well #9 9969 S 226 205 167 134 125 Well #10 10100 S 229 208 170 137 135 Well #11 10041 N 221 202 161 130 124 Well #12 9722 N 220 199 163 130 121 Average 10315 231 210 169 136 132 Maximum 11707 253 233 185 148 145 EOU Reduction 9% 27% 41% 43%

Test 2: Vertical Uncertainty

(19) Uncertainty in the vertical position can be reduced by Multi-Station analysis (MS) and by tool sag correction (SAG).

(20) TABLE-US-00003 TABLE 2 Vertical Uncertainty Vertical MWD + IFR1 + Depth MWD SAG + MS Well (ft) (ft) (ft) Well #1 10579 79 49 Well #2 10833 80 49 Well #3 10514 87 53 Well #4 10929 81 50 Well #5 11188 80 50 Well #6 11112 95 58 Well #7 10908 79 49 Well #8 10333 87 53 Well #9 10706 80 50 Well #10 11033 81 50 Well #11 10763 80 50 Well #12 10744 79 49 Average 10804 82 51 Maximum 11188 95 58 Depth Uncertainty 38% Reduction

Test 3: Mid-Point Lateral Declination

(21) Inaccurate reference declination leads to erroneous azimuth determinations for the well. This effect was investigated here by changing the well azimuth at every survey point by the difference between the BGGM declination and the IFR1 declination (first column in Table 3). One of the important additional questions to be addressed in this test was whether a single set of geomagnetic reference values could be used for the entire well path.

(22) The values in the second and third columns show the error resulting from using a single reference declination, versus using the correct declination at every survey point. It turns out that using a single reference value at the center of the lateral well gives a well path that is almost identical to the path when the correct IFR declination is used for every survey point for wells in the Bakken Field.

(23) TABLE-US-00004 TABLE 3 Mid-Point Lateral Declination IFR at IFR at No IFR Wellhead Center of Lateral Well (ft) (ft) (ft) Well #1 94.1 26.5 1.3 Well #2 38.4 10.8 0.4 Well #3 47.4 24.5 0.4 Well #4 53.7 20.4 0.6 Well #5 18.8 4.7 0.5 Well #6 24.4 12.2 0.3 Well #7 19.6 2.2 0.4 Well #8 12.4 3.1 1.1 Well #9 6.2 4.5 1.0 Well #10 41.6 13.5 0.5 Well #11 10.5 3.5 0.1 Well #12 33.3 9.6 0.5

Test 4: Different Work Flows

(24) In the previous section, it was shown that taking the reference declination at the center of the lateral gives almost the same well position as taking the reference declination at every survey point. However, the dip (magnetic inclination) and total magnetic field also have to be considered. First of all they are used as QA/QC criteria. If the total field or dip reference is inaccurate, valid surveys may inadvertently be discarded or disturbed surveys may pass QC. Furthermore, the total field and dip are also used to estimate axial interference in the so-called short collar correction. Inaccuracies in the total field and dip reference therefore generate additional errors in the well path azimuth.

(25) Table 4 shows the errors in the magnetic reference values for the lateral section, where accurate geomagnetic reference values matter the most. Three scenarios were investigated: In case there is No IFR, maximum errors amount to 262 nT for Btotal, 0.1 for the dip and 0.55 for the declination. Replacing the global BGGM value with a single IFR value at the well head reduces these errors to 163 nT for Btotal, 0.03 for the dip and 0.16 for the declination. This is a significant reduction, but the remaining error is still too large. The best result is achieved when using a single set of IFR values taken at the mid-lateral section. This reduces the errors to a negligible 19 nT for Btotal, 0.03 for the dip and 0.03 for the declination.

(26) TABLE-US-00005 TABLE 4 No IFR IFR at Well Head IFR at Center of Lateral Btotal Dip Dec Btotal Dip Dec Btotal Dip Dec Well (nT) () () (nT) () () (nT) () () Well #1 100.5 0.04 0.55 97.7 0.02 0.16 2.7 0.02 0.01 Well #2 203.5 0.05 0.23 163.4 0.01 0.07 19.4 0.01 0.01 Well #3 223.4 0.05 0.23 137.3 0.03 0.13 5.9 0.02 .0.1 Well #4 146.5 0.07 0.32 128.8 0.02 0.13 11.7 0.01 0.02 Well #5 91.0 0.04 0.12 79.4 0.01 0.04 7.8 0.01 0.02 Well #6 97.1 0.03 0.14 96.9 0.01 0.08 10.3 0.01 0.02 Well #7 108.7 0.07 0.12 113.3 0.02 0.02 11.4 0.01 0.01 Well #8 261.8 0.03 0.08 162.4 0.03 0.04 7.7 0.03 0.03 Well #9 230.0 0.08 0.06 149.0 0.03 0.05 16.8 0.01 0.03 Well #10 121.9 0.10 0.25 109.1 0.03 0.09 11 0.01 0.02 Well #11 155.8 0.06 0.07 144.1 0.01 0.03 13 0.01 0.01 Well #12 205.7 0.05 0.21 163.0 0.01 0.07 18.2 0.01 0.01 Average Error 16.2 0.06 0.20 128.7 0.02 0.08 11.3 0.01 0.02 Maximum Error 261.8 0.10 0.55 163.4 0.03 0.16 19.4 0.03 0.03

Wellbore Surveying

(27) Today, directional drillers rely primarily on real-time MWD measurements of gravitational and magnetic fields using ruggedized triaxial accelerometers and magnetometers. Other categories of survey tools include magnetic multishot tools, inclination-only tools and a family of tools based on the use of gyroscopes, or gyros. Unlike MWD tools, many of these specialty tools are run as wireline services, thus requiring cessation of the drilling process. Increasingly, however, gyroscopic tools are also being incorporated into downhole steering and surveying instruments for use while drilling.

(28) Triaxial accelerometers measure the local gravity field along three orthogonal axes. These measurements provide the inclination of the tool axis along the wellbore as well as the toolface relative to the high side of the tool. Similarly, tri-axial magnetometers measure the strength of the Earth's magnetic field along three orthogonal axes. From these measurements and the accelerometer measurements, the tool determines azimuthal orientation of the tool axis relative to magnetic north. Conversion of magnetic measurements to geographic orientation is at the heart of MWD wellbore surveying. The key measurements are magnetic dip (also called magnetic inclination), total magnetic field and magnetic declination (FIG. 4).

(29) The magnetic field associated with the Earth's crust arises from induced and remanent magnetism. The crustal fieldalso referred to as the anomaly fieldvaries in direction and strength when measured over the Earth's surface. It is relatively strong in the vicinity of ferrous and magnetic materials, such as in the oceanic crust and near concentrations of metal ores, and is the focus of geophysical mineral exploration.

(30) The technique of infield referencing (IFR) makes use of data from local magnetic surveys at or near a wellsite to characterize the crustal magnetic field, thus correcting the global model for local anomalies. Surveying engineers use IFR1 to extend the main magnetic field model and provide the best estimate of the local magnetic field, which is critical for geomagnetic referencing and multi-station drillstring compensation. These techniques allow magnetic surveying even at high latitudes, where the local magnetic field exhibits extreme variations.

(31) In more detail, the method generally entails the following steps: 1) Drilling a first wellbore having a lateral section. 2) Measuring a local magnetic declination at about midway in said lateral section using e.g. aeromagnetic surveying. 3) Combining said measured local magnetic declination with a global magnetic model to create an improved magnetic model (IMM). 4) Determining a pathway of said first wellbore using said IMM. 5) Steps 1-4 can be repeated for all or a portion of existing wellbores. 6) Drilling a second wellbore using the data generated in steps 4 and 5.

(32) In another embodiment, the method generally entails the following steps: 1) Planning an approximate first wellbore pathway having a lateral section. 2) Measuring a local magnetic declination at about midway in said planned lateral section using e.g. aeromagnetic surveying. 3) Combining said measured local magnetic declination with a global magnetic model to create an improved magnetic model (IMM). 4) Adjusting said planned approximate wellbore pathway as needed based on the data obtained in step 3 to prepare a planned improved wellbore pathway. 5) Directional drilling said planned improved wellbore pathway using the data generated in step 4.

(33) The methods of the disclosure can be applied in many different applications, including but not limited to:

(34) Wellbore Clearance/Avoidance:

(35) Twinning (also referred to as Handrail), the term given to the placement of a new wellbore in an offset parallel position to the existing wellbore for several purposes.

(36) Frac RecoveryThe term used for an application where the drilling of a lower cost replacement wellbore into the region of a costly fracture stimulation zone of an existing wellbore that has been rendered non-productive. In areas where subsurface damage has occurred, it has proven to be cost effective to twin the new wellbore into the productive zone to restore production as opposed to fracturing the well.

(37) Anti-CollisionDue to prolific number of multi-well projects both on and offshore, Anti-Collision or Collision Avoidance applications are done on a regular basis. As well spacing is critical both at surface and at depths where wellpaths cross.

(38) Ghost Well is a term used to describe the application where magnetic surveying is used to monitor the surrounding magnetic field of a new wellbore to ensure that no ghost wells are encountered. Often magnetic interference is detected at a depth where another wellbore is not supposed to be located. PMR allows the operator to determine the source and offset of the interference rather than take a chance and drill ahead.

(39) In cases where a wellbore is being directionally kicked off in proximity to magnetic interference, Kick-Off Assurance is the term used to describe the use of magnetic surveying to guide the wellbore away from the casing string or fish in the well being sidetracked or away from offset wells.

(40) Wellbore Intercept:

(41) Intercepts are when magnetic surveying is used to intentionally guide the wellbore to a direct collision course with the target wellbore. Three primary applications for Intercept are:

(42) Relief Wellamongst the most challenging applications of intercept due to the critical timeline to regain control of the blowing well and minimize environmental impact.

(43) Plug and Abandonmany wells, particularly in very old fields or in extremely corrosive environments may not be plugged conventionally due to issues related to uphole casing condition. Magnetic surveying allows a remedial well (new drill or sidetrack from existing) to intercept the damaged well at the appropriate depth(s) to satisfy abandonment requirements.

(44) Fish BypassIn some instances a fish (drillstring or casing) may become off bottom (open hole below). Magnetic surveying may be used to drill next to the fish and re-enter the open hole below the fish.

(45) Remote Operations:

(46) Often an operator is drilling in a remote area or suddenly encounters magnetic interference where none was expected. Having the ability to remote range allows the operator to have the rig send the magnetic surveying raw data over a high speed connection to a data center for remote analysis preventing costly shutdown of drilling operations and taking a chance of drilling ahead without precise knowledge of the source of interference.

(47) The following references are incorporated by reference in their entirety for all purposes.

(48) Buchanan, et al, Geomagnetic ReferencingThe Real-Time Compass for Directional Drillers, Oilfield Review, Autumn 2013, p. 32-47.

(49) U.S. Pat. No. 6,021,577 Borehole surveying [IFR2]

(50) SPE-49061-MS (1998) Williamson, H. S. et al., Application of Interpolation In-Field Referencing to Remote Offshore Locations [IFR2]

(51) SPE-30452-MS (1995) Russell, J. P., et al., Reduction of Well-Bore Positional Uncertainty Through Application of a New Geomagnetic In-Field Referencing Technique [IFR2]

(52) space.dtu.dk/english/Research/Scientific_data_and_models/Magnetic_Field_Models