Everyone knows that for oil production it is necessary to drill a well to a considerable depth. This is a complex mining construction, which does not at all look like a hole in the rock mass. Hundreds of specialists of various profiles are involved in the construction of the well.
To ensure the durability of the well, its walls are reinforced with steel pipes: direction, conductor, casing.
Legend: 1 - casing pipes, 2 - cement stone, 3 - productive formation, 4 - perforations.
The production string is lowered only into wells that are drilled in fields with proven hydrocarbon reserves and intended for field development. There are wells:
- producing - to extract hydrocarbons to the surface;
- injection - to maintain pressure in the reservoir at an optimal level;
- Estimated - to determine the reserves of oil or gas;
- observational - to control the regime of the field.
Oil well construction project
In order to open a productive oil horizon during drilling, it is necessary to take into account the geological structure of the section, the depth of the oil reservoir, the technology of opening it, the capabilities of the equipment used, the alleged complications during drilling and many more geological and technological nuances when designing a well. All this is reflected in the design of the well.
Well construction stages
Conventionally, six stages can be distinguished. At the preparatory stage, the exact geographic coordinates of the drilling point are noted, a working site is being prepared, water supply, power lines, communications, access road are being constructed, a shift camp is being built.
Then, a drilling rig and all drilling equipment are mounted on the prepared site.
The next step is the directional device, its connection with the drilling mud treatment system from sludge. Make a trial run of the mounted drilling rig.
This is followed by drilling, open-hole borehole and grouting, opening the reservoir and obtaining an influx of hydrocarbons during the test. In wells that did not give an inflow during testing during drilling, the production casing is not lowered.
Well drilling
Based on the project, the GTN is compiled - a geological and technical outfit (or an everyday plan for the drilling crew). All well construction work is carried out in strict accordance with this document. The properties of the drilling fluid, the diameter of the bit, the intervals of coring and conducting geophysical surveys - all parameters of the well sinking must correspond to those indicated in the geological and technical design.
The most important for successful penetration to the design depth are the parameters of the drilling fluid. It must keep the borehole walls from collapsing under pressure from overlying rocks, not hamper unnecessarily drilling, and when opening the productive horizon, prevent the release of hydrocarbons to the surface or gushing.
Mounting an open trunk column
During drilling, geological formations with various physical properties are opened, which do not allow further drilling without additional fastening of the well walls:
- weakly cemented rocks capable of collapsing under the pressure of a circulating drilling fluid;
- reservoir layers saturated with water, oil, gas or mixtures thereof, which must be isolated from an open wellbore.
At the opening of such intervals, the well is cemented: metal pipes are lowered to the bottom and a mixture of grouting cement and various fillers is pumped between the walls of the pipes and the well.
Depending on the design depth and geological structure of the drilling area, intermediate casing strings may additionally be required.
The design of any oil well consists of the following columns: direction, conductor, at least one casing and production string.
Completion of construction
After opening a productive formation, testing it and obtaining an influx of hydrocarbons, drilling is completed to lower the production string into the well and to grout it. The main purpose of this column is to lift hydrocarbons to the surface (if it is a producing well). Or pumping water into a reservoir under development to maintain reservoir pressure for optimal field development. Therefore, this column is called operational.
The depth of descent of the column depends on the properties of the reservoir from which oil production is planned. If the rocks of the formation are strongly cemented and stable, the bottom zone is not cemented. They install filters, which in case of clogging must be replaced. In such cases, the production string is lowered to the top of the reservoir.
If the reservoir is composed of loose rocks, oil production with an open bottomhole zone is impossible. The rock particles carried along with it will clog the open part of the trunk, and the flow of hydrocarbons will cease. In this case, the production casing is lowered to the bottom and cemented. After cement hardens, the bottomhole zone of the reservoir is perforated, restoring communication between the wellbore and the oil reservoir.
Column diameter
For oil wells, the following optimal ratios of column diameters and daily production rate were established empirically:
- less than 40 m 3 / day - 114.3 mm;
- from 40 to 100 m 3 / day - 127.0-139.7 mm;
- from 100 to 150 m 3 / day - 139.7-146.1 mm;
- from 150 to 300 m 3 / day - 168.3-177.8 mm;
- > 300m 3 / day - 177.8-193.7 mm.
The diameter of the production string is set by the customer when designing the construction of the well and depends on the expected daily production rate of oil or gas. It is these parameters that underlie all calculations for drilling, since the calculation of drill bits and casing strings is carried out from the bottom to the mouth.