Review of the Technical and Economic Evaluation of the Use of Means of Simultaneous Independent Operation for Solving Technical Problems

The Main Types of Technical Tasks

Technique designed for simultaneous separate production of oil and gas and separate water injection, including parallel or concentric production tubing, isolating packer, circulation valve, and bottomhole control devices, can be used to solve a range of technological challenges aimed at improving the technical and economic performance of liquid lifting, both in normal and challenging operating conditions [7].

This technique can solve technological tasks related to optimizing the use of reservoir energy, expanding gas energy, deep thermal water heat energy, etc. These tasks may include methods for lifting liquid from wells, separate oil and water production from a watered layer, conducting hydrodynamic reservoir studies, and exclusion of flooded layers from production. As an example, cases of using SIO technique in the oilfield practice can be considered. SIO technique is applied to utilize natural sources of compressed gas for lifting liquid from the oil reservoir using intra-well gas lift (IWGL). For IWGL implementation, a single flow column, a packer to isolate the upper reservoir from the annular space, an inter-layer isolation packer, and a bottomhole choke are commonly used, through which a specified volume of gas extracted directly from the gas reservoir is introduced into the flow column. When selecting the IWGL process scheme, geological conditions and technological parameters of field development shall be considered. IWGL is implemented in fields in Western Siberia, Turkmenistan, Saratov, and Volgograd regions: The SIO technique scheme “gas production from the gas reservoir - oil production using IWGL” is used for combined oil and gas production from respective reservoirs in a single well. In this method of well operation, two parallel production tubings are installed to separately transport gas and oil to the surface through independent channels. In some cases, the annular space is used as a channel for oil (or gas) extraction. As with all SIO technique schemes utilizing IWGL, two packers are installed in the well: an upper, isolating packer and a lower, inter-layer packer separating the reservoirs from each other [8].

SIO technique can also be used for injecting water from a high-pressure aquifer into an oil reservoir directly in the wellbore, known as intra-well water injection (IWWI), to maintain reservoir pressure. Forced intra-well water pumping from one reservoir to another is achieved using an electric centrifugal or jet pump. The downhole technique of a well-intended for IWWI includes production tubing, a crossflow coupling, and an inter-layer packer. Experimental IWWI installations have been used in Western Siberia. There have been cases of isolating a flooded reservoir by setting packers in wells (water shutoff). When perforating several production zones with a common filter and if one of the zones is fully blocked with watered, isolating it from production and separating it from other zones in the well can be achieved using packer equipment. In the wellbore, one or two production tubings and an isolating packer are installed, which is set in place (packed off) when the reservoir isolation is necessary.

With a single-row scheme, one or two packers are used, depending on the number of productive layers. The most effective method of isolating reservoirs with packers is achieved sequentially from bottom to top [9, 10]. There are also other cases of using SIO technique in the operation of multilayer reservoirs in practice.

Determining Economic Indicators

The use of SIO and DIO technique to solve specific technological challenges should undergo special technical and economic evaluation. The fundamental economic evaluation of the feasibility of using SIO and DIO technique in these cases is conducted in accordance with the “Basic Principles for Determining the Economic Efficiency of New Technique Implemented in the National Economy.” A particular problem here is to select a comparison basis and determine the initial data for calculating economic indicators (capital investments and operating costs).

This group of problems is associated with the possibility of simultaneously using production and injection wells for various technological purposes (intra-well gas lift, thermal water production with simultaneous oil heating, implementing an operation-injection-production scheme in a single well).

When using SIO and DIO technique for these purposes, the following sources of savings in capital investments can be identified [11]: Implementing intra-well gas lift eliminates the need for drilling wells to gas horizons for high-pressure gas extraction, eliminates the requirement for laying gas pipelines to supply gas to production wells and the construction of gas distribution devices, eliminates the need for gas lift equipment at wellheads.

Regarding Operating Costs: Intra-well gas lift eliminates expenses related to gas extraction, transportation to production wells, and maintenance of the gas distribution network. These sources of savings should be taken into account when determining the economic impact of intra-well gas lift. The application of downhole technique for simultaneous production of thermal water and oil to heat tubing is a promising method of operation. However, establishing the economic benefits of this method at the current stage of development poses certain difficulties. This issue should be considered in conjunction with other questions regarding the organization of reservoir temperature maintenance. The use of technique in the recovery-injection scheme can nearly always be economically justified because this scheme inherently combines two different functions - production and injection - in a single well. The source of capital investment savings from the application of this technique scheme is the exclusion of drilling one well (production or injection) and its downhole equipment [12, 13, 14].

The savings in operating costs are due to the reduction in the total depreciation of wells for oil production and water injection. When considering specific issues related to determining the economic efficiency of using SIO and DIO for solving this group of tasks, operating costs may be amended and augmented taking into account the specific conditions of oil field development.

Determining the Economic Efficiency of Incorporating Formations

The inclusion of overlying horizons, while not typically widespread, can significantly enhance current oil production, optimize the use of drilled wells at the field, and maximize oil reserves recovery. The economic outcome of implementing SIO and DIO typically involves increased well productivity and additional oil production, resulting in savings in both operational and capital costs. Capital cost savings are realized by reallocating funds earmarked for drilling upper formations or densifying well patterns on these formations (layers) as per the development plan. The reduction in operating costs from incorporating formations through SIO and DIO stems from the relative decrease in the cost of oil production per well group participating in the process compared to the cost of oil production without implementing SIO and DIO (without incorporation), considering the expected changes in the oil production process [15].

The annual economic impact of employing SIO and DIO for incorporating productive formations is determined by the savings in the mentioned costs using formula (1).

[equation]

(1) Where C1 and C2 represent the cost of producing 1 ton of oil without and with the application of SIO respectively; K1 and K2 represent the specific capital investments without and with the application of SIO respectively; C3 and K3 represent the respective cost and specific capital investment for the deposit (group of deposits) closing the industry development plan; Q1 and Q2 represent the annual oil production without and with the application of SIO respectively; ∆Q represents the additional oil production; E represents the normative coefficient of economic efficiency (0.15).

The validity of using this formula for calculating the annual economic effect can be explained by the following circumstances. The incorporation of upper productive horizons is typically carried out on already developed oil fields, with the aim of increasing the flow rates of the drilled wells. Practical experience also indicates that incorporation occurs in wells with low flow rates, considering it as a reserve for flow rate enhancement. Involvement usually targets productive reservoirs, which independent development is inefficient. Considering the above, incorporation through SIO and DIO technologies should be considered as measures aimed at improving the utilization of existing production assets [16].

It’s crucial to focus on the specifics of determining the initial data for calculating the economic effect of applying SIO and DIO technique to incorporate upper productive horizons. The net cost of oil production without SIO and DIO technique (C1) serves as the baseline in the economic effect calculation formula and reflects the economic state for the period preceding the technique application, or for the period when the technique is used, but excluding additional costs associated with operating wells equipped with SIO and DIO, as well as variable costs related to additional oil production from SIO (energy for fluid lifting, oil gathering and transfer, oil preparation) [17, 18].

Costs associated with operating wells equipped with SIO and DIO differ from regular wells due to additional expenses for depreciating specialized equipment and current repairs. These additional costs, when added to the variable costs associated with producing additional oil, determine the net cost (C2) in the economic effect calculation formula.

ΔP = (Pr.oil-C2)Q2-(Pr.oil-C1)Q1 (2)

Where ∆P represents the additional profit obtained from the application of SIO and DIO, in thousand manats; C1 and C2 represent the respective cost of oil production without and with the application of SIO, in manats per ton; Q2 represents the commercial oil production with the application of SIO, in thousand tons; Q1 represents the commercial oil production without the application of SIO, in thousand tons; Pr. oil represents the wholesale price of 1 ton of oil in manats per ton.

Additional specific capital investments in well technique with SIO and DIO consist of the cost of specialized technique (SIO and DIO), expenses for additional wellhead equipment, and are determined based on standard prices. The cost of installing underground equipment includes capital investments. An additional indicator of the economic efficiency of applying SIO and DIO is the increase in profit from additional oil production (economic benefit). This indicator is determined based on the company’s current oil prices, the cost of producing additional oil per ton, and the quantity obtained in the current year.

ΔP = (Pr.oil-C) (3)

C is a net cost of additional oil production, manats per ton.

The payback period of additional capital investments is also determined. The payback period is determined by reducing the cost of additional oil production. Incorporating zones for water injection increases the volume of water injection and contributes to the most complete extraction of oil from the involved zones. The source of savings in this case is the reduction in the net cost of injected water into the involved reservoirs. The net cost of water injection will consist of expenses for water intake and pumping, transfer to the central pumping station, which pumps water into injection wells (cost of seawater transfer), and variable costs for injection [19, 20, 21].

As the baseline cost in determining the economic effect, the cost of injection prior to the zones incorporation or the estimated cost without injection into the involved reservoirs is accepted. The latter is determined by the total expenses on injection in the conditions of involving reservoirs, excluding variable costs for additional injection into the involved reservoirs.