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From the beginning to the completion of a well, it is roughly through the process
of preparation, drilling, cementing and so on.
First, the preparatory work
(1) Fixing position
.
Determine the position of the bottom of the well according to the needs of geology or production, and make the design
.
When the shaft of the well is designed according to the plumb line, the wellhead position and the bottom position of the well are on the same vertical line, which is a straight well; If the axis of the well body deviates from the plumb line, the wellhead position and the bottom position are not on the same - plumb line, which is the directional well
.
(2) Repair of highways
.
In order to transport various equipment and materials into the well site, roads
need to be built.
Since drilling equipment is heavy material, roads should ensure access to heavy vehicles
.
(3) Flat well field
.
A square plot of land is laid out near the wellhead for construction
.
The well field area varies with the drilling rig, the shape is roughly rectangular, and the large drilling rig covers an area of about 120m in length and 90m in width; Medium-sized drilling rig covers an area of about lOOm in length and 60m in width; The size of the rig footprint can be adapted to local conditions
.
(4) Lay the foundation
.
In order to ensure that the equipment does not sink or skew during the drilling process, the foundation (or foundation bond)
is laid.
Small foundations can be made of square wood or prefabricated parts, and large foundations are poured with concrete on site
.
(5) Installation
.
Erect derricks, installation of drilling equipment, mud pumps, placement or excavation of mud ponds, etc
.
Second, drill in
Drilling in a broad sense refers to the process
from drilling to drilling a section of formation or drilling a well.
Here is only a general use of rotary drilling methods in the world to be introduced, rotary drilling methods can be roughly divided into the following processes
.
(1) Drilling in (narrow sense
).
Break the rock
directly with a drill bit.
Drill with sufficient pressure to press the drill bit onto the rock at the bottom of the well.
Feed the blade of the drill into the
rock.
The drill bit is connected to the drill string, and the drill pipe is used to drive the drill bit to rotate to break the rock, and the well will gradually deepen, and the pressure added to the drill bit is called drilling
.
The drill string transmits the power on the ground to the drill bit, so the drill string extends from the ground to the bottom of the
well.
As the well deepens, the drill pipe increases, the drill string gradually grows, and its weight gradually increases to exceed the required drilling pressure
.
Excessive drilling pressure will cause damage to the drill bit, drill pipe, equipment, and the weight of the part of the drill pipe that is greater than the drilling pressure must be suspended so that it does not act on the drill bit
.
During drilling, the pressure added to the drill bit is controlled by the drill in a timely manner to effectively and evenly drill
.
(2) Wash wells
.
The rock at the bottom of the well is broken by the drill bit to form small fragments, called drilling chips (also often referred to as sand
).
The accumulation of drilling chips will affect the drilling of new well bottoms by drilling bits, causing the mechanical drilling speed to decrease, so the drilling chips must be removed from the bottom of the well in time and carried to the surface, which is called washing the well
.
The wash fluid is injected through the inner hole of the drill pipe and flows out of the drill bit water to wash the drill bit and rush to the bottom of the
well.
The drilling chips are washed away from the bottom of the well, and the drilling chips enter the annular space between the well wall and the drill string with the washing fluid, and rise back to the ground until they reach the surface
.
The separation of drilling chips from the well wash fluid on the ground and their removal is called sand removal
.
The washing fluid that has been removed from the drilling debris is then injected into the well and recycled
.
During drilling, washing wells and breaking rocks are carried out
simultaneously.
In order to ensure the uninterrupted circulation of the washing fluid, continuous injection
with a slurry pump is required.
(3) Pick up a single root
.
In the process of drilling, with the continuous deepening of the well, the drill string should also be lengthened in time, and the next drill pipe is called a single root
.
(4) Start drilling
.
In order to replace the worn drill bit, all the drill strings must be removed from the well, replaced with new drill bits, and then re-drilled into the well to continue the operation, which is called drilling and drilling (referred to as drilling
).
A well takes a lot of drill bits to drill, so there are many
times to start and drill.
In order to improve efficiency and save time, when starting and decommissioning, it is not a single drill pipe for the connection and unloading, but three drill pipes for one unloading, called the root (or column).
Each drill pipe is 8 to 10 m long, and the length of the root is generally 26 to 30 m
.
In order to match such a long root, the height of the derrick is generally about
40m.
For other reasons, such as salvaging the bottom of the well, solving problems such as jamming drilling, etc.
, it is also necessary to drill down
.
(5) Other operations
.
During the drilling process, debris
logging, geophysical logging and formation testing are also carried out.
In general, the faster the drilling speed, the better
.
But there must also be a degree, beyond which accidents
will inevitably occur.
In drilling, accidents such as broken drill pipe and drill bit drop are often encountered, or the well wall collapses, jammed drills and so on
.
Therefore, in order to drill into an oil and gas well with high efficiency, high quality and low consumption, it is necessary to pay attention to drilling technology and implement scientific drilling
.
In the drilling engineering design, it is necessary to select a reasonable well body structure and drilling tool structure, use high-quality mud, and adopt a series of drilling techniques and measures
suitable for formation conditions.
How much pressure is applied to the drill bit when drilling? What is the rotation speed of the turntable? What is the discharge capacity of the slurry pump? This is what people often call the reasonable selection of "drilling pressure, speed, and displacement", and it is an important problem
that needs to be adjusted and solved in time with the change of well depth and formation in drilling.
- Once the well is drilled, if there are no special circumstances, it will be constructed normally in accordance with the construction design, and the well
can be delivered when drilled to the design depth.
However, it is possible that the exploration well may be drilled ahead of schedule or continued to deepen
according to new conditions emerging underground.
Third, cementing
Cementing is an important process in drilling engineering, and its fundamental purpose can be summarized as two points: strengthening the well wall (preventing shallow well wall collapse) and isolating the oil, gas and water layers of the drilling (preventing the layers from interfering with each other during exploitation).
The method of cementing is to put a seamless steel pipe called casing into the well, and pour cement slurry between the borehole and the casing to fix the casing, close the annular space between the casing and the wellbore, and separate some formations, which is the lower casing and cement injection operation
.
From start to finish, a well often needs to be lowered into a multi-layer casing and filled with cement, that is, several cementing operations
are required.
The implementation of cementing varies in different areas depending on the stratigraphic situation and well depth
.
Some can be drilled all the way to the end, and finally into the casing for a solidification and consolidation; Some wells need to be consolidated in two or three to four layers of casing, respectively, to be finally completed
.
A 4000m deep well, the design of the lower three layers of casing, the purpose and implementation steps are: the first layer for the surface casing, the depth of about 100 ~ 300m, the purpose is to seal the clay layer, quicksand layer, gravel layer, and water layer of this well section, the well in the surface casing wellhead to install a blowout prevention device, after the second drilling, switch to a drill bit smaller than the diameter of the surface casing, drill down to 2000 ~ 3000m at the stop drilling, down into the second layer of casing, called technical casing
.
The purpose of the lower technical casing is to seal the collapse layer and the high-pressure water layer, or to protect the shallow oil and gas layer, etc.
) After the third drilling, a smaller drill bit is used to drill until below the target layer, and finally into the third layer of casing, called the oil reservoir, which is mainly to create conditions
for oil testing and future oil and gas production.
Deep or ultra-deep wells sometimes require two technical casings, depending on the specific need
.
Although the wells in some areas are deeper, the stratigraphic conditions are better, and technical casing can be omitted, only the lower layer casing and oil reservoir casing can be omitted; Some areas are not too deep, if the shallow stratigraphic conditions permit, the pressure of the deep oil and gas water layer is not high, and the surface casing can be omitted, then in the whole well, there is only one layer of oil casing
.
In short, cementing should be determined according to the actual geological conditions, not only to ensure drilling safety and well quality, but also to save casing and cement as much as possible to reduce drilling costs and improve economic benefits
.
Usually after injection of cement slurry should be waiting for about 2 days, the well temperature or acoustic amplitude and other logging methods to detect the quality of cementing - cement return at the casing, cement cementing and sealing conditions, etc.
, in line with the design requirements of the cementing quality is qualified
.