In order to provide position and direction monitoring in directional bottom drilling, measuring tools are used during mwd drilling. Accurate knowledge of the spatial position of inclination and horizontal arc (Azimuth) is a vital part of directional drilling of oil wells, which is accomplished in the MWD tool. Inclination is the amount of deviation from the vertical direction (angle between the vertical line and the drilling path of the well at the desired point) and Azimuth is the amount of deviation from the north direction in the horizontal plane (angle between the horizontal image of the well path and magnetic north). Accelerometers and magnetometers (MEMS) (Microelectromechanical Systems) are used to measure these angles. MEMS is the technology of very small systems in micrometer dimensions, which is actually a combination of microelectronic technology (electronic integrated circuits) with micron machining and complex mechanical and electromechanical systems. In this way, parts of the silicon wafer are removed and new layers are added to it. Continuous integrated circuits (ICs) can be the masterminds of these systems, which can sense and control their surroundings by adding eyes and arms. The use of these systems results in low energy consumption, low cost, low volume and weight, reduced error, increased accuracy, increased reliability and increased speed. Today, all sensors and tools in the drilling industry are imported, which must be sent to the relevant companies for calibration, which is costly. Unfortunately, in Iran, there is not much history regarding the calibration of sensors in the directional drilling industry, and due to the commercial nature of such projects, access to external resources is not easily possible. We know that Iran is an oil-rich country and measuring instruments are widely used during drilling for directional drilling of oil wells. Since accelerometer and magnetometer sensors are the main components of this tool, so to increase their accuracy, these sensors need to be calibrated. The calibration process increases the accuracy of the sensor measurement and increases its reliability. So that it can be used in a wide range of temperatures and reduces the sensing error to near the level of accidental residual noise. In fact, by doing this, we consider possible errors by mathematical formulas and enter them in the sensor model so that, for example, the output vector of the acceleration sensor is adjusted by gravity acceleration. For this reason, calibration of sensors in this industry is important.
In general, the MWD system is made up of three main parts, which are:
- Inside part of MWD well which includes: 1. Power supply 2. Sensors 3. Signal transmitter and 4. Is a control system
- The data transmission section (MPT), which is actually the column in the well, through which pressure pulses are transmitted to the surface.
- The surface part that receives and decodes pressure pulses and displays the results in numbers and graphs.
Since the energy of the MWD (installed on the drilling pipe) tool inside the well is not supplied by the surface equipment, this energy must be produced inside the well. Two types of power supplies in MWD in-well tools are: 1- Lithium batteries (with a capacity of 800 ampere hours) and 2- Generator turbines. In MWD in-well tools equipped with negative pulse system, less energy is required and the battery is used as a power supply, while in positive pulse generating systems, which consume more energy, generator turbines are used. Used as a power supply. On the other hand, in systems with more sensors installed and more information being sent, more energy is required, and even in negative pulse systems, a generator turbine is used instead of a battery. Be. Also, in high temperature formations where the use of batteries is not possible, turbines have priority. Although turbines have more advantages than batteries, they are more prone to mechanical damage. Filter plates are used to protect the turbines from drilling stumps that are suspended in the drilling mud and cause damage to the blades.
MWD system positioning sensors
Almost all MWD systems use the same positioning sensors to calculate inclination, azimuth, and BHA direction. These sensors include three accelerometers perpendicular to each other and three magnetometers perpendicular to each other.
Each gravimeter measures the gravitational field component along its axis. Figure (4) schematically shows the function and components of a typical gravimeter. A piece can be moved in one direction by connecting to a hinge, and is tilted down to one side by gravity, and the current passing through a coil on it is reciprocally increased, so that by creating a magnetic state inside the coil, the weight is again in Put your former position. The amount of electrical voltage used to overcome gravity is recorded. Combining the results of all three gravimeters mounted on the three axes are used not only to calculate the inclination angle but also to calculate the azimuth angle as well as the BHA direction.
Each magnetometer sensor measures the magnetic field component along an axis. When a toroid coil is placed in an external magnetic field, an electric current is induced in its coil, the intensity of which depends on the effective surface of the coil in the magnetic field, or the angle of the toroid coil; Like the gravity sensor, this sensor measures the voltage across its electrical circuit. Unlike gravity sensors, the output voltage combinations of all three magnetometers on the three axes are used only to calculate the azimuth angle.
Surface systems (data receiving system)
All MWD systems have a pressure detector on the surface equipment that is connected to the drill pipe manifold. This detector must be sensitive enough to changes to detect very small pressure changes (in the range of 50-100 psi) in less than one second. The received and decoded pulses are then displayed and their useful information is displayed.
The simplest surface system is the positive pulse detector. When the pressure pulses of inclination, azimuth, and BHA direction reach the surface, they are decoded binary; In a period of time, each pulse represents the number one and each pulse represents the number zero. These surface systems do not require much volume and can be located in the rig control room.
The MWD system is an unavoidable part of drilling pipes and surface equipment in Western companies, while in domestic companies it is used only in special cases. Lack of purchase and operation of this system has caused a significant need to design and build it in the country. The main advantage of MWD system in drilling is receiving information from BHA position and direction in the well, without interfering with other drilling processes. In its simplest form, the MWD system is equipped with sensors that detect inclination, azimuth and BHA direction in the well; But the more advanced in-well tools of the MWD system, known as LWDs, are equipped with more sensors, some of which are sensors for determining petrophysical properties (permeability, porosity, gap distribution, etc.) and sensors for determining drilling information (drill weight). Or WOB and torque or torque). Some of these sensors are gamma-ray devices and electrical conduction detectors of the formation, and large amounts of data are transmitted to the surface through mud. The MWD system is also equipped with a data transmission system through drilling mud to the surface. The data transferred to the surface is decoded and presented in number and graph format. In addition, the data transmission system of MWD sensors without cables and electrical connections is also known as MPT (Mud pulse telemetry). Figure (6) shows a schematic of the MWD system and its components. Without using the MWD system, the BHA position in the well can be determined. In this method, the wireline tool is used and its implementation is subject to running the wireline tool, recording data and pulling it out of the drilling pipe. Typically, obtaining information from the BHA position with the old wireline method takes about 1-2 hours and with the MWD method takes about 4 minutes. Although the implementation of MWD system in drilling is much more expensive than the old wireline method, the speed of receiving information from MWD system and reducing time saving (time saving) is much more profitable than the cost of its implementation. Also, not using the wireline method in horizontal wells, as a serious limitation, has encouraged and forced drilling companies to use the MWD system. Therefore, the construction of such a system is the goal of this company.