Multi Layer Packers and Completions
V. I. Nikishov (OAO «NK “Rosneft»), A. I. Markin, R. R. Gabdulov (OOO «RN-Yuganskneftegaz»), P. I. Slivka (OOO «RN-YufaNIPIneft»)
Introduction
The field development using combined methods of exploitation of layers and creating a reliable control and regulation system of processes of production of reserves with respect to every layer is one of the main postulates of mining laws and regulations during the projection of development. Therefore at present time high emphasis is placed on technologies including the use of wells with multi-packer section arrangements designed for differential injection in geological heterogeneous production facilities [1].
Currently existing constructions of arrangements for dual injection operations (ORZ) in wells uncovering three and more layers prevent from determination of liquid flow rate of every layer without participation of the workover crew. The injection into layers is regulated after study of geophysical data and data according to well performance for a specified period of time.
The basic idea of the submitted article is the systematisation of regulation and control of the development of multilayer fields using the ORZ system. The ultimate aim is the transition to an intelligent well which enables to regulate the working conditions of layers in real-time environment and to ensure differentiated action in separate interval or area of oil reservoir.
Basic line of improvement of multi-packer arrangements ORZ
The targeted aim can be achieved at the expense of the creation of tandem of the existing technology ORZ, use of control sensors of bottom-hole parameters (pressure p and temperature T) as well as software engineering for the calculation of liquid flow rate according to the available data of pressure decrease which is the «nervous system» of the intelligent structure [2].
The following refers to the improvement elements of the construction of arrangement ORZ (fig. 1):
1. Construction modification of the bottom-hole flow bean which enables to reduce the hydraulic resistance for the purpose of increase of its throughput capacity.
2. Determination of liquid flow rate based on the calculation principle of liquid according to pressure decrease and as a consequence the creation of a software product for the calculation of liquid flow rate for injection into the layer.
3. Use of geophysical sensor systems (p, T) within the tube and the annular space of the arrangement ORZ with information transfer to the surface via cable lines.
We examine one of the main improvement elements of multi-packer system of the ORZ system. As shown in practice the liquid flow rate through a flow bean of the existing construction is limited by the diameter of the axial channel. It is possible to achieve a large flow rate through the flow bean for the guarantee of the planned regime of injection capacity by enlarging the diameter (construction modifications) of the axial channel or reducing the pressure decrease at the existing construction.
Figure 1 shows comparative schemes of the arrangement ORZ in use (a) and the improved arrangement ORZ (b).
Fig. 1. Schemes of the arrangement ORZ in use (a) and the improved arrangement ORZ (b)
For analyse it is recommended to compare two versions of flow bean construction with different types of orifice instruments (SU) (table 1).
The orifice instruments in the form of Venturi tubes make it possible to increase the throughput capacity of the flow bean at the expense of the reduction of decrease in pressure by the overcoming resistance to the fluid stream. It can be accepted that the fractional decrease in pressure is 5 — 20 % for Venturi tubes generally.
In case of flow motion the friction head loss lengthwise and the overcoming local resistance is often observed at the same time. The total head loss is determined as arithmetic loss sum of these types.
The hydraulic calculation is presented for flow beans of the existing construction (in the form of a restricted channel) and in the form of Venturi tubes. Due to small sizes and high seed of the liquid stream the following assumptions can be added to the calculations:
— the existing flow bean represents an orifice plate of a wide, even lengthwise restricted part of the channel;
— the friction pressure loss is equal to zero.
The theory about the liquid flow through nozzles supposes that the average speed of the stream increases together with its restriction and the static pressure becomes less than the static pressure before the orifice plates/Venturi tubes. The pressure difference (differential pressure) becomes higher if the flow environment increases. So it can serve as flow measure [3-5]. Table 2 shows the methodology algorithm of the flow bean at differential pressure.
The use of the flow bean in arrangements ORZ is limited by the size of the flow area of 9.5 mm. The use of orifice instruments in the form of Venturi tubes under equal conditions makes it possible to increase the liquid flow rate through the flow bean up to 39%. Table 3 shows a comparative calculation of two versions of flow bean.
Employing the trail-and-error method of number values, i.e. changing the diameter of the existing flow bean it is easy to calculate the equivalent diameter (11.56 mm) of the restrictive channel which would guarantee a liquid flow rate of 659.28 m3/day. The result of the calculations is the dependence of the liquid flow rate on the differential pressure for two versions of flow bean.
Figure 2 shows that the flow bean in the form of Venturi tubes has a higher throughput capacity in comparison to the flow beans in use. Charts which are shown in figure 3 are used for the sake of simplicity of determination of the liquid flow rate for different flow bean diameters and the value of differential pressure. The throughput capacity of the flow bean does practically not depend on the production material of the orifice instruments and measuring pipe and depends largely just on the surface finish characteristics, the wear-resistant and corrosion behaviour of the materials. An alternative solution for the increase of throughput capacity for the Priobsk field is often the use of an extension pipe without a
Fig. 2. Dependence of the liquid flow rate on the differential pressure for Venturi tubes (1) and orifice plates (2)
Fig. 3. Charts for determination of the liquid flow rate through the flow bean in the form of Venturi tubes (measuring pipe diameter — 20 mm; material of SU and the measuring pipe — 40X)
borehole chamber and cap. However, the given solution is in conflict with the company specification concerning the engineering requirements on the organisation ORZ of water at the Priobsk field in the injection wells which uncovered several sites (No. P1-01 S-034 JuL-99) according to which the following tests must be carried out after the first running-in and installation of equipment in the well for the separate water injection:
- pressure test of the oilwell tubing columns;
- reliability control of the performance of packers in terms of lack of fluid crossflow;
- regulation operations with a view to ensuring the planned injection conditions including the performance of geophysical studies.
Another important constituent of pressure loss in the construction of flow bean is the presence of local resistance occurring in zones of tube section changes or travelling direction of the liquid stream. This loss depends on the average speed and the cross-sectional dimensions of fluid jet, forms and sizes of the barrier, its placing in relation to the fluid jet.
Taking into account the consistency of mass of the liquid flow rate and neglecting the friction hydraulic resistance the Weisbach formula can be used for the determination of local loss [6-7]
∆p = ξ ,
where ξ – local pressure loss; p — fluid density; v — average speed (as a rule after the pass-through through the local resistance).
The determined theoretical coefficient values of local resistance for a number of cases (sudden contraction, orifice plate, etc.) comply with the test data completely.
For the purpose of adaptation of the calculation procedure of the flow bean autonomous pressure sensors in the arrangements ORZ which make it possible to register pressure in annular space (between the production string and the arrangement ORZ) were installed in the well 6295 of the Priobsk field on 22 June 2008. The pressure in the tubes (before the entry into the flow bean) and the actual flow were determined according to the field geophysical survey. For the complete adaptation of the calculation methodology it is necessary to have statistics of the survey under different conditions.
The largest resistance becomes evident in the case of peg-leg of liquid stream. When using the flow bean where the liquid changes the direction by 90º abruptly after having left the orifice instruments the pressure decrease is 6.29 MPa, then the pressure decreases 3 times like before the exit at an angle of 45º. As a result small changes to the construction of the flow bean were recommended; in particular the directions of the liquid entry and exit out of the flow bean have changed (fig. 4).
Body 1 of the regulating device is connected to the gripping head 2 and the tail 3. The tail 3 contains a gas lens 4. The gripping head 2 and tail 3 have sealing elements 5. The regulating device contains fluid passages, in addition, axial channels 6-8 are connected to side channels 9-11: in the tail are the axial channel 6 and the side channel 9, in the body are the channels 7 and 10 and in the head the channels 8 and 11 correspondingly.
Under the sealing elements and the gas lens is an axial channel which has restrictions 12, 13 by objective reasons. This is related to the fact that it is necessary to have space groove with some deepness for fastening of sealing rings 5 and a cementing collar of the gas lens 4.
For the reduction of resistance from restriction and the increase of its throughput capacity at the entry of restriction 14, 16 and exit of the restriction 15, 17 bevelled flowing wills 14-17 are installed which make it possible to minimise the internal hydraulic resistance what increases the throughput capacity, reduces the flow bean effect as well as the running time, reduces significant corrosion in the restriction zone.
The use of the recommended flow bean construction under equal conditions makes it possible
Fig. 4. Construction of a double-sided flow bean taking into consideration the integrated rework
to increase the liquid flow rate through the flow bean to 30-35% at the expense of loss reduction by overcoming the hydraulic resistance.
Another improvement direction of the arrangement ORZ is data acquisition from geophysical sensors on a real-time basis (see fig. 1). This project was initiated within the scope of the established working group Systems of New Technologies in the OAO HK «Rosneft». The introduced technologies ORZ in two layers and more than one well and with one downhole equipment has no analogue in the domestic and foreign oilfield practice. This work is carried out in wells with an internal diameter of the production string of 146 mm. The whole downhole equipment is drained of in one run.
At the moment at OOO «RN-Yuganskneftegaz» operations of the first stage of ORZ are carried out on the Priobsk field in the wells 8709/2016 and 7730/201a. The main tasks which will be decided during the performance of work are: lowering of the multi-packer section arrangement with sensors (p, T) in one run; acquisition of geophysical data (p, T) on a real-time basis; inspection of reliability of the entire system; detection and prevention of risks; transition to the final stage of «intellectualisation» of ORZ (fig. 5).
The stage-by stage approach of the operations is defined by the complexity of the operations to be carried out and the degree of intellectualisation of the well.
Conclusion
1. The current development state of the majority of multilayer fields is characterised by the ever-increasing demand for the use of technologies which make it to maintain separate account of products to be lifted and to be injected.
2. The improvement of technology ORZ is based on the creation of tandem of the existing technologies of geophysical control of layer parameters and the mathematical devices of calculation of hydrodynamic processes taking place at the boundary of well — layer.
3. The changes to the existing arrangement must relate to all elements of the system ORZ. At OOO «RN-Yuganskneftegaz» in association with OOO NPO «Novye Heftyanye Tekhnologii» a flow bean was developed which makes it possible to increase the flow rate to 30-35% in comparison to the flow beans used today.
4. Calculation methodology of the liquid flow rate according to the differential pressure is being developed jointly. According to the results of the collection of statistical material it is planned to develop a software product which makes it possible to carry out operational supervision of the flow bean operation without the involvement of geophysics.
5. At the moment operations are being carried out in the wells of Priobsk field. The performance of operations concerning the technological advancement of ORZ is divided in stages which are defined by the complexity of operations to be carried out and the degree of intellectualisation of the well.
6. A judgement must be passed on the economic efficiency of the implementation of the improved arrangement ORZ on the basis of the whole «life» cycle of the well.
Fig. 5. Transmitted-data circuit
However, the main effect of the project is linked to the raise of the coefficient of oil recovery to the expense of isolation of zones or intervals with harsh water breakthroughs.
7. The improvement of the technology ORZ is a relative recent trend both in Russia and abroad (in our situation in columns of 146 mm) due to lack of experience with the use of technology under real conditions. Therefore for this direction a more deepened approach is necessary in order to become an effective instrument concerning the control of water flood at multilayer fields. OOO «RN-Yuganskneftegaz» makes preparation for an adaptation of technology for two layer wells («annular tube») which enable to maintain accounts of injected liquid immediately from the collar.
8. The improvement of technology ORZ is one step of the development of intellectualisation of oil production and differentiated water injection into heterogeneous geological objects. The company «Rosneft» is engaged in this at the moment.
List of references
1. Leonov V.A., Sharifov M.Z., Garinov O.M. ORRNEO Technology (Single Commingle Development of Several Production Zones) Introduction Experience on Oil Fields in Western Siberia/OOO NII «SibGeoTech»// SPE-104338
2. Lukyanov E.E., Kayurov K.N. Operation intellectualisation of injection and exploitation wells when using multi-packer arrangements for simultaneous injection and exploitation on multilayer wells//Karotazhnik. 2005. — No. 5. — p. 270-275.
3. GOST 8.586.1-2005 (ISO 5167-1:2003). Measurement of liquids and gases flow rate and quantity by means of orifice instruments. Part 1.
4. GOST 8.586.2-2005 (ISO 5167-2:2003). Measurement of liquids and gases flow rate and quantity by means of orifice instruments. Part 2.
5. GOST 8.586.4-2005 (ISO 5167-4:2003). Measurement of liquids and gases flow rate and quantity by means of orifice instruments. Part 4.
6. Rabinovich E.Z., Evgenyevich A.E., Hydraulics: 3rd ed. revised and amended. M.: Nedra, 1987. — 224 p.
7. Altshul A.D. Hydraulic resistance: 2nd ed. revised and amended. M.: Nedra, 1982. — 224 p.
