Spontaneous well deviation

Spontaneous well deviation, i.e. well bore deviation from vertical is often encountered in the process of drilling vertical wells using rotation method. Deviation of vertical wells results in a number of problems: interruption of planned spacing for development of oil and gas fields, increased deterioration of drill pipe, worsening of quality of cement squeeze job, impossibility to use sucker-rod pumps for well operation, etc.

Causes of well deviation include geological, technical and technological factors. Geological factors include presence in well profiles of steeply dipping formations; frequent change of rocks with various hardness; presence in rocks through which the well is drilled of fractures and caverns. Technical factors contributing to well deviation include misalignment between drilling derrick axis and rotor center and well axis; inclined position of rotary table; application of bent drill pipe, etc. Technological factors causing well deviation include setting of extremely high pivotal loads on the bit; incompliance of bit type, volume and quality of wash fluid with nature of rocks being drilled.

In compliance with the above-mentioned factors measures to prevent well deviation must be taken. Under complicated geological conditions a specific drilling string bottom hole assembly including calibrators and centralizers is applied. In addition, the following is required:

• implementation of equipment installation according to technical specifications;

• selection of bit type according to rock type;

• reduction of a load on the bit, etc.

Text 8

Read, translate the text "Water flooding" and make the annotation of it.

Water flooding

In many of the oilfields natural reservoir energy has fallen to such low levels that wells will not produce at a rate high enough to justify their maintenance. In some of these fields methods of restoring or injecting energy into the reservoir are used to increase the oil recovered from them - these methods are known as a secondary recovery.

One of the more common methods used is "water Hooding". Each oil well is normally surrounded by a few water-injection wells. Water is pumped through these injection wells into the oil reservoir, spreads out from the injection wells and moves toward the oil wells, driving reservoir oil ahead of it. This system is continued until the fluid taken from the producing wells becomes all or mostly all water.

There are other less common methods of secondary recovery, including gas cycling, repressuring by gas injection, and pressure maintenance by gas or water injection. In all these systems a similar principle is used - the injection of energy into a reservoir through use of liquid or gas under pressure.

Text 9

Read, translate the text "Completion methods" and make the annotation of it.

Completion methods

The methods of preparing an oil well to produce are different and depend upon the kind of oil reservoir. If the well is drilled in hard rocks, the oil-producing zone may be left entirely open, with no perforated casing or liner used to protect the hole. In loose, soft sands it may be necessary to cement the production casing at the top of the producing zone and use a perforated liner. This liner is a string of casing that does not reach to the surface and is usually suspended from the bottom of the production casing.

The purpose of the liner is to keep sand and solids out of the well, yet allow the passage of oil and gas into the well. In case there are several oil-producing zones at different depths, the production casing may be run to the entire depth of the well, and then perforated opposite the horizon to be produced. Bullet perforation is performed by shooting metal bullets through the casing so that holes are left in the casing at the desired depth. Cumulative perforation uses specially shaped charges rather than bullets to perforate the casing.

One of the most common types of completion consists of setting the production casing through the producing formation, cementing it in place, and then perforating the casing and cement opposite the producing formation.

Another type is multiple completions, a process by which it is possible to produce from different pay zones through the same well bore. This provides for obtaining the maximum amount of oil with the minimum use of casing.

Text 10

Read, translate the text "Formation stimulation" and make the annotation of it.