Improving the Accuracy and Reliability of MWD/Magnetic-Wellbore-Directional Surveying in the Barents Sea

Abstract

The years ahead will see increased petroleum-related activity in the Barents Sea, with operations far off the coast of Norway.The region is at high geomagnetic latitude in the auroral zone, and therefore, directional drilling by use of magnetic reference will experience enlarged azimuth uncertainty compared with operations in the Norwegian and North Seas. Two main contributors to azimuth uncertainty are magnetic disturbances from electric currents in the ionosphere and axial magnetic interference from the drillstring. The former is more frequent in the Barents Sea than farther south, and the effect of the latter is increased because of diminished value of the magnetic horizontal component. Wellbore directional surveying for operations on the continental shelf in the North Sea and the Norwegian Sea rely on wellestablished procedures for near-real-time magnetic monitoring by use of onshore magnetic-reference stations. The different land and sea configuration, distant offshore oil and gas fields, higher geomagnetic latitude, and different behavior of the magnetic field require the procedures to be reassessed before being applied to the Barents Sea. To reduce drilling delays, procedures must be implemented to enable efficient management of magnetic disturbances. In some areas of the Barents Sea, the management requires new equipment to be developed and tested before drilling, such as seabed magnetometer stations. One simple way to reduce drillstring interference is increasing the amount of nonmagnetic steel in the bottomhole assembly (BHA). To maintain azimuth uncertainty at an acceptable level in northern areas, it is crucial that wellbore-directional-surveying requirements are given high priority and considered early during well planning. During the development phase of an oil and gas field, the planned wells must be assigned adequate positional-uncertainty models and, if possible, be designed in a direction that minimizes the wellbore directional uncertainty.

Effects of substorm electrojet on declination along concurrent geomagnetic latitudes in the northern auroral zone

“…One must keep in mind that although the fluctuations in total field and inclination might be within acceptable tolerances, the effect on the declination could be relatively large and lasting, without being detected at the rig site. According to Ekseth et al (2006) there are no simple ways to directly quality check declination variations. From a directional drilling perspective, a constant declination offset from the quiet level for several hours can have a devastating effect on the wellbore position and the result can be missed geological targets and anti-collision situations (Edvardsen et al 2014).…”

“…According to Ekseth et al (2006) there are no simple ways to directly quality check declination variations. From a directional drilling perspective, a constant declination offset from the quiet level for several hours can have a devastating effect on the wellbore position and the result can be missed geological targets and anti-collision situations (Edvardsen et al 2014). In such cases, data on the geomagnetic variations at a nearby observatory or variometer should be used to monitor the situation, and if applicable, corrections should be made (Edvardsen et al 2013).…”

“…For survey systems, when using the geomagnetic field to determine azimuth with true or grid north as the reference, any error in the estimation of the declination will automatically be an error in the final azimuth. Unexpected errors in the declination might cause the well to miss the underground geological targets, meant to optimize reservoir exploitation, and may increase the risk of unintended collision with other wells (Edvardsen et al 2014). It is standard practice to quantify the potential error in the declination as an uncertainty and use it as an input for the calculation of wellbore positional uncertainty.…”

“…Qualitatively, as shown later in Figure 4, the sign and magnitude of the fluctuations in the declination (DD) are influenced by both the magnitude of the local horizontal magnetic field component and D 0 . A theory on how the declination is affected by the external magnetic field in the auroral zone was outlined by Edvardsen et al (2014). Since both the dipole declination and declination vary spatially according to the position on the Earth's surface, the signature of identical substorms may vary as a function of longitude in certain representations in the local coordinate system (e.g.…”

Design and Algorithm Verification of a Gyroscope-Based Inertial Navigation System for Small-Diameter Spaces in Multilateral Horizontal Drilling Applications

“…Since such INS is a type of dead-reckoning system which needs to integrate the outputs of inertial sensors for the calculation of orientation and position, INS is characterized by short-term high accuracy and long-term error accumulation [14]. Even high-accuracy INS operating in an unaided mode may produce 5000 ft. position error per hour due to sensor's error and bias accumulation [15]. Moreover, stochastic noise at the output of the gyroscopes additionally and significantly deteriorates the accuracy of this orientation solution, so building an appropriate built in terms of the system dynamics for fine alignment.…”