An optimal drilling operation requires close control over a number of parameters.Even though the drilling program may have recommendations related to drilling parameters, it is mandatory that rig personnel (e.g., driller, drilling supervisor, drilling and mud engineer) keep track of the operation development at all times in order to make necessary adjustments and to quickly detect and correct drilling problems.
A modern rig will have devices that display and simultaneously record most of the important parameters related to the drilling operation. Parameters that cannot be determined automatically, such as mud properties, will be measured, recorded, and controlled constantly as well. Some of the most important parameters include:
- Well depth
- Weight on bit
- Rotary speed
- Rotary torque
- Pump pressure
- Pump rate
- Fluid-fl ow rate
- Flow return
- Rate of penetration
- Hookload
- Fluid properties (e.g., density, temperature, viscosity, gas and sand content, salinity, solids content)
- Pit level
Monitoring of these important parameters, together with reliable historical records of previous similar operations, will assist the driller in predicting and detecting possible drilling problems. Monitoring the mud system is an important task that must be fulfi lled to maintain well control. The mud gives warning signs and indications of kicks that can be used to reduce the severity of the kicks by early detection, avoiding a large influx of gas into the wellbore. Additionally, if the system is properly monitored, other drilling problems such as lost circulation can be minimized.
Moreover, good records of various aspects of the drilling operation also can aid geological, engineering, and supervisory personnel. Today, modern rigs carry centralized well-monitoring systems that can be housed in the engineer’s office and/or in the geologist’s offi ce at the rigsite. Besides, if desired, advancements in satellite communications allow installation of monitoring systems in places far from the rigsite.
These monitoring units provide detailed information about the formation being drilled and the fl uids being circulated to the surface in the mud, and they centralize the record keeping of drilling parameters. The mud logger carefully inspects rock cuttings taken from the shale shaker at regular intervals and maintains a log describing their appearance. Additional cuttings are labeled according to their depth and are saved for further study by the paleontologist. The identifi cation of the microfossils present in the cuttings assists the geologist in correlating the formations being drilled. Gas samples removed from the mud are analyzed by the mud logger using a gas chromatograph. The presence of a hydrocarbon reservoir often can be detected by this type of analysis.
With the development of downhole tools specially designed for well inclination and direction control, operations in directional wells became much more efficient. These tools are run together with the BHA and will constantly send information to surface regarding the position of the well. Measurement-while-drilling (MWD) tools normally use a mud pulser that sends information to the surface by means of coded pressure pulses in the drilling fluid contained in the drillstring. Chapter 8 provides information on MWD equipment.
