Drilling for oil and gas is a complex process. The videos below provide basic knowledge of the drilling process. Before drilling, the site must be carefully chosen. Then the land is prepared and access roads should also be built. A reserve pit must also be dug on the ground for the disposing of mud and rock. The next step is arranging the rig equipment. When the rig is complete set up, workers can begin the drilling operation.
The analysis and processing of all this large mass of information provides the drilling engineers with the essential elements for drawing up the drilling program.
These data are available from existing documents such as:
Every well has its own specific features (depth, exploratory, development or appraisal well, onshore or offshore, vertical, directional or horizontal..) but the basic criteria are the same for all well types.
The first step to be taken by engineers to work out the drilling programme is to construct, the trend of the pressure gradient curves according to depth (geostatic, pore pressure and fracture gradients) to design the well casing profile.
Choice of rig, wellhead and BOP
The casing levels, the diameters and weight of the strings, the pressures and temperatures concerned, and the volumes of drilling mud to be used, are all aspects participating in determining the choice of rig type, blowout prevention systems (BOP, choke manifold, hydraulic circuit) and wellheads.
The choice of rig is closely bound up with the depth it is wished to reach and with the weight of the strings concerned.
According to the weights of the strings to be handled, rigs are used that have different characteristics, and what is of basic importance is the strength of the whole assembly, (travelling block, crown block, hook and derrick floor) from which the string hangs while being lowered into the well.
In offshore activity, the choice of the rig is determined, not only by the weight of the strings, but also by the depth of the water in the area of operations.
Drilling rigs installed on offshore vessels or platforms are built to reach the maximum possible depths and have all the material and equipment necessary for drilling on board.
The composition of the wellhead depends on the pressures that can be reached during the various working phases – both drilling and production – and on the diameters of the strings to be lowered into the well.
Control of drilling operations
The great complexity of the drilling process, its high costs, the need to ensure the full efficiency of the rig and the respecting of safety and of the environment call for a continuous optimizing of operations, which are achieved through the monitoring and processing of all available data, both geological and drilling.
To reach these objectives, every drilling rig, and in particular those that have to drill complex, deep and therefore costly wells, is endowed with more or less sophisticated mud logging units, which permit – through appropriate sensors and the activity of specialized personnel – the acquisition, processing and interpretation of a vast range of information of interest both to the geologist and to the drilling engineer.
Mud logging units are equipped with sensors, positioned in appropriate parts of the rig, permitting the automatic, continuous acquisition of the most significant parameters, and advanced information systems, based also on expert systems, as the means of managing operations in real time, with the consequent reduction of time and costs.