The cellar represents the dugout that is a few feet subsurface, this facilitates the setting of the conductor casing, and the mounting of the wellhead. Now the subsurface placement of the wellhead facilitates the mounting of the production and valve tree at near surface level thus facilitating easy access and operation. The cellar allows for the appropriate spacing of the topside assembly such that the key areas for operation are easily accessible.
The cellar’s function is not limited to the production stage, it is important during the drilling stage as well. However its function is similar to that of during the production stage it facilitates the spacing out and accommodation of drilling equipment specifically the blow out preventers (BOPs) or “stack”.
The cellar can serve informally as a catchment for returns from the well bore during the drilling process. Normally all returns from the wellbore during drilling is handled by the rig fluid/mud system, however in the event of gas, pressure variations, making or breaking of connections, casing fill up or simply runing into the hole mud/drilling fluid invariable may spill over the conductior or riser of the “stack”. The cellar provides an area to collect the fluid so that a hazard or environmental issue is avoided. It also prevents the loss of the fluid in general, thus facilitating its recovery as it can be pumped out of the cellar and returend to the system for treatment or at the very least pumped away for better safer disposal.
Argueably though the cellar serves the purpose of facilitating the mounting of the prduction tree at a height and level that is convenient to operation and further work on the well.
The wellhead is the first of the topside equipement and is the base for all the other topside equipment that will be mounted to and used to interface with the wellbore. It represents the suspension point for the casing strings and tubulars used in the wellbore and is the place where the wellbore is sealed thus preventing pressure release to the topside environment.
The wellhead usually sits within the cellar, and is comprised of the base plate and casing head at the bottom. Building upon this are the casing spools eventually being topped by the tubing head. The wellhead assembly allows for access to the annular space of the various casing strings, but at the same time facilitating the proper sealing of the wellbore. It is the mounting point for the production tree and allows for the termination of the various tubulars thus allowing for any number of fluid control devices to be mounted a top.
