Scale factor represents distortion from a mapping system since the Earth is mapped into a flat surface, but the actual surface is in curvature. Figure 1 illustrates a scale factor with a reference location of the Earth’s surface. If the location is above the map projection plan, the scale factor will be less than 1.0. However, if the location is below the mapping projection, the scale factor will be more than 1.0. A scale factor less than 1 means that the actual distance on the Earth’s surface is longer than the actual distance on the map. Whereas, the scale factor of more than 1 demonstrates that the actual distance on the Earth is shorter than the map distance.
Universal Transverse Mercator (UTM) is one of the commonly used map projection methods in directional drilling. In UTM, the world is divided up into 60 zones between 84° North and 80° South and East-West from 180 degrees longitude. Then the Earth is flattened with the Zone 1 starting at 180 E-W longitude. Since the earth is divided into 60 zone so each zone has 6 degree wide. Figure 1 illustrates the concept of UTM and Figure 2 shows the UTM grid. This method will not cover the polar region.
Figure 1 – Universal Transverse Mercator Diagram
Figure 2 – The Universal Transverse Mercator (UTM) grid
Zones are numbers from 1 to 60 and the zone 31 has 0 degree meridian (Greenwich, England) on the left and 6 degree East on the right (Figure 3). Each one in UTM is divided into grid sections which cover 8 degrees of latitude and the system uses letters from C to X, excluding I and O.
Directional drilling maps are flat, but the Earth is an oblate spheroid. This leads to a challenge to accurately represent the wellbore position on the Earth on a piece of paper. In this section, you will learn about mapping techniques used in directional drilling, limitations and the errors of mapping techniques.
One of the most important concepts of mapping is latitude and longitude.
Latitude is a coordinate used to specify the north-south position of a location on the surface of the Earth. Latitude is an angle which starts from 0° at the equator to 90° at the Earth North-South poles. It is simply defined like this;
0 ° at the equator
+90 ° at the North pole
-90 ° at the South pole
To define latitude, it is described in degrees, minutes and seconds. Parallel line of latitude is a small circle at particular latitude which is parallel with the Equator.
Directional drilling relies on mapping system to accurately identify location of the wells. Therefore, it is very important to learn the basics of mapping and other relevant information. This topic is about Geodetic Datum.
The Earth is not a complete sphere shape but it is actually Oblate Spheroid (“Spheroid”). It means that the shape of the Earth is almost a sphere. It can be proven from the fact that the equatorial diameter (the longest diameter) is approximately 12,756 km and the diameter from the North Pole to the South Pole is approximately 12,714 km (Figure 1). Additionally, the Earth has a different attitude based on location. So, people developed a model to help describe the Earth, which is called “Geodetic Datums”.
This is one of excellent VDO demonstrating shock and vibration in the drillstring by Schlumberger. In this VDO, you will learn about mechanisms of shock and vibration, types of whirls and how these will damage your drillstring and BHA. Moreover, we provide the VDO transcript to help you get more understand about the content of this VDO as well.