Comparison of Magnetic Single-Shot Instruments With a Directional MWD System
- T.J. Mitrou (Aminoil USA) | F.A. Stone (Aminoil USA) | M.L. McCarter (Aminoil USA) | Bill Buss (Aminoil USA)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- April 1986
- Document Type
- Journal Paper
- 163 - 168
- 1986. Society of Petroleum Engineers
- 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6.1 Drilling Operation Management, 1.10 Drilling Equipment, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 1.6.6 Directional Drilling, 1.12.1 Measurement While Drilling, 1.6 Drilling Operations, 4.3.4 Scale, 1.9.4 Survey Tools
- 0 in the last 30 days
- 222 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
Summary. A measurement-while-drilling (MWD) directional survey tool and a set of magnetic single-shot instruments used while drilling a particular, highly deviated well were removed from the field and put in a controlled laboratory environment. Tests were conducted to compare directional-survey azimuth readings obtained with the single-shots against azimuth readings taken with the MWD system. We found both measuring systems were generally accurate and repeatable; but we observed differences in azimuth readings that sometimes exceeded l degree under even ideal test conditions. The MWD tool was more repeatable and, on average, somewhat more accurate.
Oil company personnel and directional drillers are growing more accustomed to using mud-pulse telemetry MWD tools for directional surveying in lieu of magnetic single-shots (which had dominated the directional measurement market since 1934). Frequently, a directional driller will run a single-shot on top of the MWD tool to obtain a crosscheck. But MWD systems and single-shot devices do not always produce identical azimuth readings downhole, and this leads to questions about azimuth differences. (Usually, discrepancies in inclination-angle readings are quite small or nonexistent.)
An opportunity to examine differences between MWD and single-shot survey readings arose when Aminoil USA questioned some azimuth-angle discrepancies observed during drilling. Both the oil company and Teleco Oilfield Services Inc., the MWD company, decided that ideally the single-shot instruments and the MWD system in question should be compared under the best possible conditions to eliminate extraneous causes of discrepancies. One such factor is magnetic interference caused by the drillstring. When a single-shot is run on top of an MWD system, the distance from each of the compasses (in the case of the MWD system, its "compass" is really a magnetometer) to the nearest magnetic metal in the drillstring is different. In some circumstances, the unequal distances can cause differences in azimuth readings between the two systems. Other factors that exist in the field include (1) alignment of the survey instrument within its drill collar, (2) alignment of the drill collar in the borehole, (3) whether the specific nonmagnetic drill collars in use have any magnetic hot spots that are located where they could affect azimuth readings, and (4) how precisely one can read the single-shot film. We did not want to test laboratory-specimen equipment but rather to test the specific hardware used in drilling the well that triggered the study. Therefore the MWD system and the single-shot instruments used to drill the well were set aside specifically for this study. Neither the MWD system nor the single-shot devices received any special tune-up or other special preparation before the tests.
We conducted this test in a laboratory environment created specifically for testing magnetic survey instrumentation. We wanted to be sure any observed differences were attributable strictly to the survey tools rather than our test procedures or equipment. procedures or equipment. Nonmagnetic Environment. Our tests were performed in Teleco's sensor calibration building in Meriden, CT, a structure designed and built to be free of magnetic anomalies. When this building was constructed, magnetic field surveys were made before the site was selected, several times during construction, and again after construction to ensure that the building remained free of any magnetic field problems. The building has wooden beams instead of steel beams, concrete without steel reinforcement, aluminum nails instead of iron, plastic conduit, etc. Similar buildings are used for directional sensor calibration at our field maintenance facilities.
Aligmment of Test Fixture. The test fixture must be accurately aligned relative to magnetic north. A Model DIM-100TM inclination and declination magnetometer is used for this purpose. The DIM-100 is a precision instrument of the same type used by the U.S. Dept. of the Interior Geomagnetic Survey Team.
|File Size||398 KB||Number of Pages||6|