Olexander Denysyuk
Chief Engineer, NTP Burova Tekhnika LLC

Oil and gas wells are quite complex facilities which construction is carried out in various mining and geological conditions, and the cost of construction is hundreds of millions of UAH.

The effective construction of the well starts with making the most optimal design decisions and is determined by the technological feasibility of the decisions made and the reliability of the outgoing information. The important role is assigned to the best practices of project development at fields with different geological and geophysical conditions of drilling. In this regard, our company’s experience of developing more than 150 projects provides the Customer with the most optimal solutions.
The development of design estimates for the construction of wells in terms of designing and financing new advanced technologies can historically be divided into the following stages:
The first stage - when, in Soviet times, design estimates could be transferred to the bank, and the financing of the well-drilling project could be opened, which was an indicator of its reliability and importance, but the latest technologies and developments mainly took place in a science, based on a separate financing, and were rarely brought to a broad introduction.
Beginning in the 90s of the last century, design priorities moved toward getting arbitrary solutions. The use of advanced technologies, equipment and tools was not a priority either for designers or drilling divisions that were part of producing companies Ukrnafta and Ukrgazvydobuvannya and funded basically on a residual principle, after the purchase of casing pipes, chemical reagents and drill bits.
An example of another system brought by foreign experts - РРС as a private foreign-owned company: when the project and well-drilling programme for the controlling organizations were at the wells, drilling and mounting technologies were implemented within the Drilling Program and the separate budget.
The second stage – that Burova Tekhnika, like all Ukrainians, run «in its way» - when for drilling wells in the Pryluky oil-bearing region Ukrnafta PJSC, being the Customer, voiced its order - drill crewes and grouting services should be provided by Pryluky DD, casing string and wellhead equipment – by Ukrnafta, and the rest, including the development of the project and its practical implementation - by Burova Tekhnika. «Your design - your implementation, but performance indicator must be high». Based on this scheme, we have drilled over 50 wells, 42 of them - with a horizontal wellbore. In order to ensure the successfull well drilling, we had to use the modern MWD systems equipped with a hydrocanal, РDС bits, Canadian engines, polymer solutions and so on yet at the design stage. By the way, as our company is multifaceted, in various cases we act as a developer of a work project, as a service company or as a general contractor. Quite often these options are combined. In other words, we developed the project documentation as close as possible to the actual drilling, including the estimates, according to which the Customer entered into Agreements with the Contractors (DD, Log Analysts, Burova Tekhnika, Suppliers of Casing Pipes, Wellhead Equipment, etc.) and supervised the compliance of the actual and the design cost of the well.
The development of the third stage is due to a significant increase in drilling volumes and is stipulated by the need of Customers to involve service and drilling international companies on a tender basis. At this stage, the requirements became more strict for the development of design documentation, which would ensure the formation of the basic requirements for technologies and drilling equipment that encourage obtaining high performance indicator and a reliable construction - the oil and gas well, and would provide a real budget to implement the project.
For reference, even today we have already formed the basic approaches to projects ordered by leading companies (DTEK, UGV), it comes to:
- development and coordination of terms of reference and pre-design decisions;
- request for tender to select a drilling contractor and service companies;
- adjustment of project solutions and considering programs of service companies that won a tender on various types of work, examinations and author’s control over the implementation of project solutions.
Accordingly, the role of design organizations in providing the efficient process for the construction of wells undergoes a rise.
Considering the role and importance of the separate stages of the construction of deep oil and gas wells, one is required to highlight the choice of the well design and mounting that determine the reliability and durability of the well as a capital facility to produce oil, gas, condensate and provide the opportunity for multiple operations to intensify the flow, deal with the reservoir, move to other horizons, including side-tracking, etc.
The design of the well is determined by the number of casing string, the depth of their installation, the diameter of casing pipes, the diameter of bits, the height of lifting the cementing slurry in the annular space, the use of packer elements of different types and bottomhole design.
In general case, characteristics of the above list of indicators when choosing a well design depend on a set of regulated and unregulated factors. Unregulated factors include field geological conditions: the depth of occurrence of productive reservoirs, their productivity and collecting properties; reservoir and pore pressure of hydraulic fracturing of rocks that form a section; physical and mechanical properties and state of rocks disclosed in terms of various complications, etc.
Regulated factors include the purpose and method of drilling, the number of productive horizons to be tested, the way of disclosing productive horizons, financial capabilities of the Customer to apply certain technologies and equipment.
The design of the well largely determines the possibility of bringing the well to the design depth and affects the technical and economic performance of the well construction.
The main vectors to optimize the designs of deep oil and gas wells and the process of mounting at the design stage are:
- designing a 245 mm casing string as an operating one with subsequent landing of 1 or 2 liners. With this design, the metal capacity of the well decreases and the possibility of a full-fledged side-tracking and subsequent casing is provided. It also provides for less time spent to construct wells caused by a decrease in time for mounting and reequipment of the mouth and provides the possibility of using a drill tool of greater diameter when drilling at great depths, which in turn creates the possibility of implementation of powerful hydraulic programs. An illustrative example of the implementation of this approach is one of the largest oil fields in Ukraine, wells at which were constructed for a long time under a «classic» 3-casing design, which at the moment is replaced by a new one that provides all of the above advantages, as well as the possibility of landing a 245 casing string and faster output of products, which reduces the payback time of the well.
Other optimization methods are:
- wall cementing of large diameter casing string;
- using cementing slurry with minimal water removal based on expanding mixtures;
- using liner hangers, which design includes packer systems of various types, for the reliable sealing of the annular space;
- using elements of casing mountings drilled-out by PDC bits;
- if any high-pressure gas horizons, the design of casing pipes with premium-class high-performance thread using the Bestolife sealing grease;
- to ensure high quality of centering casing string, the design of hard centrators and turbolizers, cementing baskets;
- if any complex geological conditions in well log, the design of using rotating pad device or rotating liner hanger complete with side spiral reinforcement pad device;
- applying operating liner filters using packer systems to separate water-holding and productive horizons to avoid contamination of the productive horizon and additional costs for perforation;
- introduction of the elements of multi-sectional arrangements for further multi-stage hydraulic fracturing or overlapping of individual intervals in case of their flooding.
At present, when issues of ecology and land allocation are becoming increasingly acute, the actual trends in field development are cluster drilling and multiple drilling.
Well construction under multiple drilling technology provides the following advantages:
- the total cost of work runs down since drilling is initially carried out to a certain depth, after which horizontal branches are added;
- oil output grows per one drilling rig;
- availability of several wellbores allows developing collector on a larger area;
- more accurate estimation of the current inventory volumes;
- reducing the number of wells on the surface, respectively, reduces environmental damage.
This technology, however, is a large-scale and resource-intensive project, which requires a detailed study of the collector at the initial stage. In some cases, for example, offshore drilling, multiple technology practically has no alternative. Burova Tekhnika, by the way, has experience in designing such a well.
Cluster drilling, when the wellheads are located on the common ground, and the wellbottoms - in accordance with the geological grid of the field development, the following benefits are provided:
- reducing resources and time to arrange sites for drilling rigs, access roads and other communications;
- reducing time spent on derrick construction;
- reducing environmental costs.
However, the construction of wells requires additional solutions. Thus, NTP Burova Tekhnika has developed a technological regulation that provides for the installation of wellhead equipment in mineshafts with protective caps and the construction of underground pipelines to ensure safe operation of already drilled wells and simultaneous drilling of new ones.