mudlog

Cuttings
As a well is drilled, rock cuttings are taken out of the hole by the drilling flluid. These cutting are collected at the shaker area and then analysed under a microscope. The type of rock, colour and hardness are among the properties that are recorded. Other tests can be done to idenitify if there are traces of oil on the cuttings. Part of the sample is put in bags and sent to the geologist in town for further evaluation

Gas. Also carried up the hole in the drilling fluid is gas. Gas comes from gas or oil. There is usually always some gas present, but a high level of gas can mean a gas zone or an oil zone has been drilled. As the drilling mud comes out of the hole it travels under a metal box called a gas trap. The gas trap agitates the mud with spinning rod and liberates the gas from the mud. The gas is then sucked into the mudlogging unit with a vacuum pump and sent to two types of gas analysers. One analyser burns all the gas and in doing so detects how much gas is present. The second analyser is a chromatograph. This also burns the gas but breaks it down into the diffenent types. C1 methane, C2 ethane, C3 Propane, C4 butane and C5 Pentane. The different ratios of these types are used to estimate the type of hydrocarbons, gas or oil.
The mudlogger must make sure all the gas equipment is working properly, calibrate the equipment and make sure the values are recorded in the database. He/she must monitor the gas levels at all times and alert the driller and oil company representave if gas levels become high.

Sensors. The mud loggers have many sensors around the rig to measure many things. Each sensor has a wire running to the mudlogging unit that carries the signal. These signals are read by computers and stored in a database. The mudlogger must make sure all the sensors are working properly, that each one is calibrated, that the signal reaches the computer and that the computer reads the signal properly and store the value in the database.

The sensor readings include the rpm of the bit, the weight of the all the drillpipe in the hole, the temperature of the mud coming out of the hole, the density of the mud, the pressure exerted by the pump pumps. There are many pits on the rig that hold the mud on surface. There are sensors in each pit to measure exactly how much mud in in each

Mud Pit Levels and Well Control
The deeper a hole is drilled the higher the pressures become. The density of the mud (weight for each gallon) is controlled to counteract the pressures of the hole. Sometimes the pressure in the hole increases faster than expected or sometimes an oil or gas zone is suddenly drilled with high pressure. When this happens gas or oil can enter into the hole. This will force mud up and out of the hole . Normally the mud coming out of the hole goes into a mud pit and then is pumped down the hole again. During a normal oparation the level in the pit will stay the same as mud is pumped out of the pit, down the drillpipe, past the bit, up the hole and back into the pit. The exact amount of mud in that mud pit is measured by the mudlogger's sensor and monitored by the mudlogger on a computer screen. If gas enters the hole and displaces mud out of the hole, faster than normal, there will be more mud in the mud pit. The mud pit readings which are displayed on the computer screen have alarms set to beep if the pit level rises. If this occurs, it is called a "kick". If a "kick"is not detected and stopped by increasing the densiy of the mud, a blowout will occur. A blowout is when all the mud is forced out of the hole and only gas present under pressure.
The mudlogger must always be aware of how much mud is in the pit at all times. On some rigs he/she cannot leave the work area for even a minute, unless another mudlogger is present.

Collected data. All data measured by the sensors is automatically stored in a database. Data from analysing the cuttings is hand entered into the computer database. As the data is read, many calculations are made by the computer. For example by reading the height block the exact depth of the bit and the rate of drilling is calculated. There are hundreds of calculations done. All this data is stored in the database. As the data is collected and calculated it is displayed on monitors and computer screens around the rig so everyone can keep track of what is happening. On some rigs the mudlogger's computers are on an internal network to shore. The link is made with satellite signals. People in town can also see what is happening. Indeed on some jobs the data is fed into an internet site and with a login and password the data can be viewed anywhere in the world. The mugloggers also recieve data from other companies (ie MWD) and can then sent their data forward. All this data is also stored in computer database to be used to prepare reports and logs. It is the mudlogger duty to make sure all this data is stored properly in the database. He/she must also make sure all the network links are working and that the correct data is send around the rig, to the office in town, and possible around the world.