The article will be devoted to the process that begins immediately after the productive formations in the field zone are examined by all available methods. This is a well completion. In the article we will define this process, highlight its conditions, scheme, and consider the classification of completion types. We will dwell in detail on some methods, analyzing their advantages and disadvantages.
Definition
Completion of wells is a complex of processes for opening reservoirs of various rocks, the subsequent consolidation of the bottom hole, stimulation of the inflow, and most importantly, the development of the desired mineral deposits.
Along with development, the characteristics of many reservoirs are also evaluated. The process is done in many ways. Among the most common - multi-face, casing, without the use of casing. The second of these completion methods is the most common and widely applicable. For each type, different technologies are used, which can be classified by type of work, type of equipment used and other criteria.
Process Conditions
Before deciding on the technology of well completion, specialists formulate the conditions of the reservoir. They will affect the entire project, well construction.
When designing completion, you must first pay attention to the following factors:
- The position of the gas-oil contacts.
- The position of the oil-water contacts.
- The thickness of the most productive formation.
- The presence of cracks and their orientation in space.
- Homogeneity.
- Relative permeability.
- Impermeable obstacles that are in the way of fluid movement.
The description of the deposit determines:
- Type of completion.
- The position of the well section in the reservoir.
- The need for a pilot barrel.
- Tolerances for a given corridor.
Types of Completion
There are several classifications of well completion systems. We list the most common of them.
By geological characteristics:
- Horizontal
- Vertical.
- Directional wells.
By appointment:
- Discharge.
- Fountain.
- Mechanized.
- Artificial elevators.
By design:
- Cased trunk.
- Open trunk.
- Perforated barrel.
In a separate category, one can distinguish well completion with AVPT, AVPD, as well as multi-layer completion.
Schema definition
The completion scheme for an oil well must necessarily be compatible with the conditions of the reservoir, consistent with its scope. It is important to take into account the requirements of current and major repairs, which will be needed in the future. It may be necessary to cut off some of the intervals for work to intensify the flow. Or you need to finish the work of waterlogged intervals.
The choice of one or another scheme directly affects the diameter of the well, the radius of its curvature, the intensity of the set of zenith angle. After defining the scheme, it is already possible to complete the design of the well as a whole. But the design is designed to casing all areas of complications long before drilling the final section.
The casing installation depth is primarily determined by the well design. The specialist here relies on the stability of the walls, pore pressure, on the requirements that are associated with the gradients of hydraulic fracturing and pressure.
The design profile of the directional well must necessarily be compatible with the diameters of the casing strings and the depth of installation of the shoe of such a string. In some cases, the already established diameters of the casing strings, the actual well, and also the depth of the shoe can be changed to better adapt them to the requirements of the well profile.
Next, we will provide descriptions of well completion schemes - with open, closed, and also mixed-hole.
Open face
With this method of completion, the operation is carried out without a casing installed in the oil field. The casing will be lowered into the well , but only to the top of the production interval. Oil will flow to the surface through tubing.
The advantages of such a scheme are as follows:
- Simple construction.
- High degree of hydrodynamic perfection.
- Low cost.
- Excellent access to fractures in reservoir rocks.
- Radial type of fluid flow into the well.
There are also disadvantages:
- The clay crust will affect the productivity of the well until its walls are clean.
- The produced fluid passes through all the damaged areas-intervals.
- The walls of the open bore interval are not protected from collapse.
- There is no insulation of various materials.
Features of the open-hole scheme
Additionally, the method is divided into the following subspecies:
- Open face.
- Open face with a filter.
- Open face with plug-in filter.
It is also important to highlight the following features of the scheme:
- The casing necessarily overlaps the upper layer. Otherwise, there is a risk of damage to the well by the upper layers as a result of a collapse, the flow of unwanted fluids into the wellbore.
- Insulation of materials is not possible. Thus, if a certain interval needs to be cut off or subjected to processing to intensify the inflows, its isolation becomes unrealistic.
- Hydrocarbons directly enter the wellbore. The latter must be strong enough to withstand their influx.
- The fluid must pass through the bottomhole damaged zone. But the clay crust in this case, as we have already said, will inevitably reduce the productivity of the well.
Closed face
Most wells around the world end with a closed hole. It is mainly applicable for heterogeneous reservoirs, where stable and unstable rocks change, as well as gas and water displacement layers characterized by different reservoir pressures.
The following advantages of the scheme are highlighted:
- No clay peel is needed.
- The trunk is protected from collapses.
- When making the correct perforation calculations, bypass the damaged areas.
- With good cement quality, good tightness will be observed.
- Excellent isolation of intervals and zones.
- Possibility of multi-layer well completion.
But there are significant disadvantages:
- A skin effect may occur due to the barrel not being 360 degrees open.
- High cost of completion.
- Permeability deterioration due to perforation of productive material and drilling debris.
Mixed type circuit
Such completion (the face is only partially blocked by the column) is distinguished by two important distinguishing features:
- It is used in a homogeneous deposit in a stable collector to isolate those pressure horizons that are located close to the roof of objects.
- The design is supplemented by an insert filter in cases where the collector is unstable, but the deposits are homogeneous. It also isolates pressure horizons located in close proximity to the roof of objects.
Completion methods
The following methods of completion of wells (horizontal, vertical, deviated) are distinguished:
- Classical technology using perforated columns.
- Multi-layer completion.
- Mastering using stationary devices.
- Finishing with clipping sandstone.
- Completion with cutting off the gas, water reservoir.
We will analyze them in more detail below.
Classic way
With standard completion, a pipe or column is lowered from the surface into the well leading either to the bottom or to the formation, which was determined to be the most productive in the study. The casing is then treated directly in place by cementing.
The use of stationary devices
What kind of completion equipment is involved here? The installation of columns, pipes, ground equipment. At the same time, all other work on completion, as well as repairs, are carried out using the small size of the tools already inside the tubing.
So they will perforate, cement (to seal leaking sections in the column), and fill with gravel (to further strengthen the column, protect it from sand). One of the advantages of this technology is the low cost of work.
Multi-layer development
In some cases, along the length of the well, it is discovered that not one but several layers are productive. Specialists resort to this technology to extract gas or oil immediately from a complex of saturated horizons.
The method is more common for state-owned companies. The technology is also applicable when it is necessary to control the functionality of the collector.
Development with sandstone clipping
If the field is located in loose soil with a high sand content, the process of its development is somewhat more complicated than in other cases. After all, the ingress of sand can damage equipment, clog the layers to such an extent that development ceases to be profitable.
The use of pumping equipment helps the situation. These are the two main ways:
- Gravel filling of a well.
- The use of liner columns having slots or perforations.
Mastering with cutoff of gas and water
When completing wells, other products are obtained along with oil. In all cases, even before the sale, they try to separate water and oil. The gas content is also reduced or completely removed.
Well completion here is done so that free components do not fall into the finished product. To do this, you must correctly select the depth of lowering the column within a given area.
We examined the basic schemes and types of well completion. So that development does not become unprofitable, it is important to correctly determine this method of completion for a particular case.