Oil Well Drilling oil and gas issue for better technology

Wellheads can be Dry or Subsea completion. Dry Completion means that the well is onshore on the topside structure on an offshore installation. Subsea wellheads are located under water on a special sea bed template. The wellhead consists of the pieces of equipment mounted at the opening of the well to regulate and monitor the extraction of hydrocarbons from the underground formation. It also prevents leaking of oil or natural gas out of the well, and prevents blowouts due to high pressure formations. Formations that are under high pressure typically require wellheads that can withstand a great deal of upward pressure from the escaping gases and liquids. These wellheads must be able to withstand pressures of up to 140 MPa (1400 Bar). The wellhead consists of three components: the casing head, the tubing head, and the ‘Christmas tree’ Photo: Vetco international

A typical Christmas tree composed of a master gate valve, a pressure gauge, a wing valve, a swab valve and a choke is shown here. The Christmas tree may also have a number of check valves. The functions of these devices are explained in the following paragraphs. Ill: Vetco international At the bottom we find the Casing Head and casing Hangers. The casing will be screwed, bolted or welded to the hanger. Several valves and plugs will normally be fitted to give access to the casing. This will permit the casing to be opened, closed, bled down, and, in some cases, allow the flowing well to be produced through the casing as well as the tubing. The valve can be used to determine leaks in casing, tubing or the packer, and will also be used for lift gas injection into the casing.

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Crude Oil is a complex mixture consisting of up to 200 or more different organic compounds, mostly hydrocarbons. Different crude contain different combinations and concentrations of these various compounds. The API (American petroleum institute) gravity of a particular crude is merely a measure of its specific gravity, or density. The higher the API number, expressed as degrees API, the less dense (lighter, thinner) the crude. Conversely, the lower the degrees API, the more dense (heavier, thicker) the crude. Crude from different fields and from different formations within a field can be similar in composition or be significantly different.

In addition to API grade and hydrocarbons, crude is characterized for other non wanted elements like sulfur which is regulated and needs to be removed. Crude oil API gravities typically range from 7 to 52 corresponding to about 970 kg/m3 to 750 kg/m3, but most fall in the 20 to 45 API gravity range. Although light crude (i.e., 40-45 degree API) is good, lighter crude (i.e., 46 degree API and above) is not necessarily better for a typical refinery. Looking at the chemical composition of crude, as the crude gets lighter than 40-45 degrees API, it contains shorter molecules, or less of the desired compounds useful as high octane gasoline and diesel fuel, the production of which most refiners try to maximize. Likewise, as crude gets heavier than 35 degrees API, it contains longer and bigger molecules that are not useful as high octane gasoline and diesel fuel without further processing.

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Reaming is a high risk operation which accounts for a large proportion of stuck pipe incidents. If reaming operations are conducted too fast solids from wash-outs and cavings are introduced into the circulating system at a faster rate than the hole is being cleaned. This results in a pack-off. Do not assume that any resistance is always at the bit; stabilisers and drill collar contact may be indicative of a build up of loose material in the hole and a potential pack-off situation. The following guidelines are offered as a general list.

Stuck pipe prevention

Planning
a1. Have a contingency plan for all possible problems. E.g., what to do in case of a leaking swivel packing or leaking saver sub.
a2. Always pre-plan a trip. Have an up-to-date mudlog on the rig floor. Know where high doglegs exist and note troublesome areas from past trips. Utilise the mud loggers’ paper model of the BHA and well bore previously mentioned.
a3. Have singles in the V-door in case downward motion is required to free the pipe after a connection.

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Proper use of mud pills may improve hole cleaning in a high angle well. High viscosity (preferably weighted ) pills are often effective in hole sizes larger than 81/2″ whilst low viscosity pills are beneficial in smaller holes. When using a low viscosity pill, it is important to maintain the normal high flow rate and minimise non-circulation time. Also it is often necessary for a low viscosity pill be followed by a high viscosity (weighted) pill in order to ensure adequate hole cleaning in the larger diameter vertical hole section. The specific pill volumes should be determined based on the hole size and the calculated effect on hydrostatic head.

Note : The use of low viscosity, turbulent flow pills is not recommended in weakly consolidated formations as washout or hole collapse may occur.

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