For multi-layer deposits, options for joint and independent reservoir development with the allocation of basic operational facilities and areas, return facilities are being considered. In practice, there are often cases of economically justified operation of two different formations with different properties, combined into one development object and operated by one grid of wells (a common filter). Sometimes another operational object is attached to the main object in separate wells (zones), the development of which by an independent grid is economically inefficient. At the same time, the minimum allowable oil reserves per well from the point of view of economics are provided. Such an introduction is forced and leads to a decrease in the oil recovery coefficient (ORC) [1].
Many wells that exploit the underlying horizons, when making a decision to transfer them to the overlying objects, do not fully fulfill their purpose. The work of many of them is characterized by low profitability due to high water availability. To achieve the design values of the ORC, it is necessary to continue the operation of wells, and at the maximum possible modes.
At the same time, dual completion (DC) of formations (objects) through one well (group of wells) is a complex of technical and technological measures that allow through wells to affect each object of a multi-layer deposit in order to ensure its production in an optimal mode. Dual completion, in turn, can be divided into dual completion injection (DCI) of the displacing liquid and dual completion (DC) extraction (DCE) of products from each shared productive object.
The DC of wells in multi-layer deposits is one of the main methods of regulating development. The creation of independent systems for the development of facilities using the technology of simultaneous and separate operation is a purposeful change in the conditions for the development of productive formations within the framework of the technological solutions adopted.
DCI of the displacing agent into formations with different geological and physical characteristics provides injection of the agent in the necessary volumes to maintain reservoir pressure (MRP) at a differentiated injection pressure (repression), and DCE - extraction of the necessary volumes of reservoir production by creating a corresponding depression for each formation.
When developing a field, the allocation of operational facilities is of great importance. Due to the difference in sediments by the conditions of occurrence, the type of reservoirs, and the properties of saturating fluids, it is necessary to identify objects for which the use of DC is recommended. When selecting objects, the following geological and commercial characteristics are usually taken into account:
- type of collector, its physical properties;
- the mode of operation of the deposit, its size, reserves;
- difference of compositions and properties of saturating fluids;
- the relative position of productive layers along the section.
When operating several layers of one object with a common filter, it is technically and technologically more difficult to control and influence the development process. The complication of the development control conditions may lead to a decrease in the ORC of formations, difficulties in accounting for the production of individual formations. When combining objects into one in the mining process, the following problems may arise [2].
- The introduction of layers of low permeable deposits to highly permeable reservoirs leads to the disconnection of the latter, the joint processing of the bottom-hole zone of non-homogeneous layers complicates the process of regulating development.
- Due to the mutual influence of closely located layers, low-permeable ones are turned off from operation. For joint development of objects, their permeability should not differ by more than 2-3 times. The inclusion of different layers in one development object is possible with similar values of the parameters of the layers and the products contained in them.
The reserves of the Northern Goturdepe deposit are multi-layered. The oil and gas potential of the Northern Goturdepe field is associated with deposits of the Absheron (Ia, Ib, Ib), Akchagyl (IIa, IIb) tiers, upper (IIIa), middle (VIII, IX) and lower krasnotsvet (NK, NK-l +2, NK-3+4, NK-5, NK-6, NK-7a, NK-7b, NK-8, NK-9, NK-10). The deposits of the Absheron-Agchagylsky tiers are concentrated in the eastern part of the site, the deposits of the upper and lower sections of the red-colored sediments are concentrated in its western and northwestern parts. The deposits of the Northern Goturdepe are stratified, arched, tectonically shielded.
The general information of the deposit has been studied and scientifically analyzed. The geological structure, stratigraphy, tectonics of the Northern Goturdepe deposit and reservoir properties of the rocks of this deposit have been fully studied. Hydrodynamic analyses of reserves of horizontal wells at the Goturdepe field and productive layers extracted from previously operating wells were carried out.
The analyses carried out in the work on the geology and hydrodynamic reserves of formations, as well as on the productivity of these formations of the Goturdepinsky field, forming the deep essence of future work, laid the foundation for a highly effective correct development of the well design for the method of simultaneous separate operation of several layers, successful drilling of wells to the design depth, selection of appropriate solutions, in order to uncollate productive formations, achieving their high oil recovery in the development process.
The geology of the deposit and the hydrodynamic reserve of productive layers, as well as the analyses carried out on the productive capacity of these layers, the successful drilling of 4 wells to the design depth and their commissioning during testing for the method of simultaneous separate operation of several layers according to the results of the work proved their correct execution.
And also, the technical and technological differences of the method of simultaneous separate operation of several layers from the currently operating method of development of productive layers are scientifically analyzed, and detailed theoretical and practical materials about this method are also collected and the results are obtained.
In order to introduce into the production of the DC method of several layers, the necessary exact geological and expected during operation parameters of each formation of the developed field have been fully studied.
Taking into account the location of the North Goturdepe field in shallow water, in order to reduce investment costs during development and drilling, as well as during operation, it was decided that the field should be developed by the DC method.
Due to the fact that more than half of all capital investments are accounted for by drilling wells, there is always a question of combining formations or facilities for operation with one grid of wells. Joint development of two objects by one well (common filter) is usually carried out for economic reasons, when their separate operation is unprofitable. At the same time, as a rule, it is not possible to realize the potential of each operational facility, and the total value of the debits is significantly lower (by 20-40%).
Thus, the use of DC technology is relevant for multi-layer deposits. However, the creation of a joint reservoir development system requires a serious feasibility and geological study, taking into account the mutual influence of dual completion facilities and the compatibility of chemical properties of fluids and physical parameters of the overall system.
It is desirable to solve the issue of joint operation of reservoirs using the DC technology at the first stages of development, which allows you to save significant funds for drilling wells. In addition, at the dual completion of several facilities with one well should be planned already at the stage of justification in the project documents for the development of the field, where it should be provided:
- uniform drilling of the field (deposits);
- rational and efficient use of approved reserves of oil, gas and related components;
- prevention of selective mining, leading to losses of balance reserves;
- reasonable allocation of operational facilities for independent development.
At the design stage, it is necessary to select wells in which the DC will be used, form a grid of wells, and determine other parameters of the development system. The allocation of operational facilities must be linked to the possibilities of transforming the impact system in the process of developing reserves, the possibilities of introducing various methods of increasing oil recovery without prejudice to other facilities.
Of great importance is the depression on each formation, which in turn depends on the reservoir pressure of each object and the limitation of bottom-hole pressures that will be common to jointly operated objects. There is a potential possibility of interplastic flows.
The production of wells is characterized by a complex of physico-chemical properties, different depending on the horizon. It should be borne in mind that when fluids with different properties are extracted together, new components may form that complicate subsequent processes of transport and product preparation. With separate selection with the establishment of optimal bottom-hole pressure, it is possible to select products from a reservoir with reduced reservoir pressure, as well as from a reservoir in which oil has structural and mechanical properties.
When implementing equipment for DC, strict requirements are imposed on the design and technical condition of the production columns of wells. Production from the layers, depending on the number of layers to be separated and the design of wells, is extracted by one or two elevators. The supply of the working agent to the separated layers can be provided by pumping fresh, sewage, reservoir water from the surface or by passing reservoir water with rising to the surface, or by downhole pumping.
DC is used for the development of various objects and is necessary for those formations (one development object) whose operation by a common filter is undesirable from the point of view of geological and field parameters. When working together with high- and low-permeable (if they are present in the section) layers of the object, it is advisable to operate this object using the DC technology, dividing it into two parts (high- and low-permeable layers).
Accounting for the production of reserves (development control) of simultaneously-separately operated facilities is carried out on the constructed geological and hydrodynamic models by summing up the remaining oil reserves in all wells (formations) as a whole for the simulated object and checking the fulfillment of the material balance
where Z is the balance reserves, respectively, residual and initial in the whole object;
– accumulated oil production in the whole facility.
By repeated modeling, the fulfillment of the material balance condition is achieved with a given accuracy (an error of no more than 0.1%).
