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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:

1. pressure test of the oilwell tubing columns;
2. reliability control of the performance of packers in terms of lack of fluid crossflow;
3. 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.

Labels: Intelligent well completions, packers, Rosneft, Russia oil gas

posted by The Rogtec Team @ 14:28  2 Comments

Andrey Bakulin and Mikko Jaaskelainen, Shell, and Alexander Sidorov and Boris Kashtan, St. Petersburg State University

Real-Time Completion Monitoring (RTCM) is a new non-intrusive surveillance method for identifying permeability impairment in sand-screened completions that utilizes acoustic signals sent via the fluid column. These signals are carried by tube waves that move borehole fluid back and forth radially across the completion layers. Such tube waves are capable of "instant" testing of the presence or absence of fluid communication across the completion and are sensitive to changes occurring in sand screens, gravel sand, perforations, and possibly the reservoir. That part of the completion with differing impairment from its neighbors will carry tube waves with modified signatures (velocity, attenuation). The RTCM method would require permanent acoustic sensors and, thus, could be thought of as "miniaturized" 4D seismic and "permanent log" in an individual wellbore.

Introduction

Completions lie at the heart of deepwater production and constitute a large portion of the overall well cost. Great multidisciplinary effort is put in up front to design wells right. This contrasts greatly with the production stage, where little information is available to detect problems, optimise the inflow and prevent expensive workovers. Sand screen plugging, incomplete packing, development of "hot spots" in screens, destabilization of the annular pack, fines migration, near-wellbore damage, crossflow, differential depletion, compartmentalization, and compaction represent a typical list of challenges that are extremely difficult to decipher based on several permanent pressure and temperature gauges alone.

The aim of our study was to develop RTCM as a new method that can characterise permeability impairment of the sand screen, gravel, perforations, and the immediate near-wellbore space.

Principles

Physical principles that allow for the estimation of permeability from acoustics waves are well-known for open boreholes where permeability from Stoneley wave became the only direct technique of estimating in-situ permeability from wireline logs. Tube or Stoneley wave is a fundamental axisymmetric mode that represents a piston-like motion of the fluid column resisted by the borehole wall. When tube waves encounter a permeable region, their signatures change since the radial motion of the fluid is no longer fully resisted by the borehole wall and part of the fluid can escape in and out of the formation (Figure 1a). This implies that tube-wave velocity decreases and attenuation increases with increasing fluid mobility (ratio of permeability to viscosity). RTCM extends ideas of open-hole Stoneley-wave logging to wells with sand-screened completions typical for deepwater. These wells have additional layers between the formation and borehole fluid, such as sand screen, gravel sand, and casing (Figure 1b). The sand screen and gravel pack prevent migration of reservoir sand into the wellbore and maintain the integrity of the reservoir around the wellbore. The completed well has one essential similarity to the open-hole model, i.e., in a normal flowing well there has to be fluid communication across all layers of the completion. Our objective was to analyse the effect of broken fluid communication across the sand screen (or perforations) through the signatures of tube waves.

Figure 1: (a) The tube wave attenuates and slows down when it encounters the permeable interval that can exchange fluids between borehole and formation. (b) Schematic cross-section of a sand-screened completion in deepwater well. Sand screens: c) slotted PVC screen used in this experiment; d) a premium screen, named as Excluder (from Baker), e) wire-wrapped PVC screen.

RTCM concept

Figure 2 depicts two possible configurations of the RTCM method: "repeated or permanent log" (transmission) and "mini-4D seismic in a well" (reflection). In both cases, we detected changes in acoustic signatures of tube waves over time and inferred changes of permeability along the completion. In transmission configuration, we measure velocity and attenuation of the tube waves(s) along the completion and thus need sensors along the sandface (Figure 2a). In reflection configuration, we need sensors only above the completion and analyse the change in reflected arrivals from permeability interfaces (Figure 2b).

Figure 2: Conceptual design of RTCM configurations:

a) "Repeated or permanent log" (transmission configuration); b) "Mini-4D seismic in a well" (reflection configuration).

It can be shown that such measurements can be performed while the well is flowing, thus providing valuable information in real time to well engineers and production technologists. Such information allows them to detect changes in permeability in and around the well (and thus the inflow ability) in real time,
identify the well structure responsible for any problems (screen, perforation, etc.),
help design best practices for drawing the wells without impairing them,
raise red flags early on when problems are not acute and can be fixed with lighter effort, and help characterize cross-flow and differential depletion in wells with multiple commingled producing intervals.

We conducted a full-scale laboratory test of the RTCM concept when permeability impairment is caused by sand-screen plugging in a completion without agravel pack.

Full-scale laboratory test

The schematics and an actual photo of the horizontal flowloop setup we used for experimental measurements are shown in Figure 3. The outer pipe (casing) is modeled with glass pipe. The inner pipe (PVC sand screen) is positioned inside using plastic centralisers.

Figure 3: (a) Sketch of the flowloop setup with the model of sand-screened completion in horizontal well. (b) Photograph of the actual setup with a glass outer pipe (no perforations).

To model an open sand screen ("open pores"), we used a PVC pipe with 0.0002 m slots (Figure 1c). The plugged sand screen was modeled with a blank PVC pipe without slots and is referred to as "closed pores". The annulus between the inner and the outer pipe is filled with water. Measurements are conducted with a 24-level hydrophone array (35 cm spacing) and a piezoelectric source, both lying down at the bottom of the inner pipe.

Idealized completion model

Actual sand screens can be quite complicated (Figure 1d), but we assume that the screen can be represented by a homogeneous effective pipe, both in terms of mechanical and hydraulic properties. If this pipe is not permeable (plugged screen), then the laboratory setup can be simplified to this idealized four-layered model: fluid-elastic inner pipe (screen) Р fluid-elastic outer pipe (casing). This model of two concentric elastic pipes with a free outer boundary supports four axisymmetric wave modes at low frequencies:

li>TI tube wave supported by the inner pipe

• TO - tube wave supported by the outer pipe


• PI - plate (extensional) wave related to the inner pipe


• PO plate (extensional) wave related to the outer pipe.
  

Figure 4: Pressure seismograms with successive amplifications for a four-layered model with closed pores (no gravel pack) using model with glass outer pipe and plastic inner pipes. (a) The largest arrival is a fast tube wave (TO - 1030 m/s) related to the outer glass pipe. (b) The smaller arrival is a slow tube wave (TI - 270 m/s) related to the plastic inner pipe. (c) Plate waves are of even smaller amplitude (brown PO - 5410 m/s, green PI - 1630 m/s).

Figures 4 shows synthetic seismograms for a four-layered model similar to the experimental setup. The dominant arrival is a fast-tube wave associated with the outer pipe (TO), whereas the slow-tube wave supported by the inner pipe (TI) is weaker. If the inner pipe becomes permeable (open to flow sand screen), then both tube waves experience attenuation and slow-down.

"Permanent or repeated log" (transmission)

Let us look first at transmission signatures Р velocity and attenuation Р in the presence of open and plugged screens. Figure 5a shows the raw data recorded in the case of no screen and a screen with "open" or "closed" pores. Despite pipe joint reflections, there are clear differences between three scenarios. First, in the absence of a screen, there is only one (fast) tube wave present with a velocity of about 1050 m/s.

It experienced some amplitude loss, possibly due to intrinsic attenuation in the recording cable. When an impermeable inner pipe was added (closed pores), a slow tube wave appeared, and the fast tube wave became more attenuative. When the inner pipe became slotted (open pores), then fluid on both sides of the PVC screen started to communicate, and this led to a very strong attenuation of both tube waves. Thus, a greatly increased attenuation of both fast and slow tube waves was the first-order diagnostic for open screens, whereas reduced attenuation was characteristic for plugged screens.

Additional diagnostics can be established by analyzing energy distribution as a function of frequency between these two cases. Figure 5b shows slowness-frequency displays. Both fast and slow tube waves with approximately the same velocities of 1100 m/s and 350 m/s are clearly seen in the plugged and open cases, however, the slow wave is completely absent without a screen. In a plugged screen, the fast wave carries maximum energy in the frequency range of 300-600 Hz close to the dominant frequency of the source, whereas lower and higher frequencies carry less energy. In contrast, the spectrum of the fast wave in an open screen has a big energy "hole" between 300 and 600 Hz where the fast wave is attenuated so strongly that even higher frequencies (600-900 Hz) carry more energy. This behavior suggests that fast-wave energy is severely attenuated in the medium frequency range, whereas it is still preserved in the high-frequency range.

Figure 5: Seismograms (a) and slowness-frequency displays (b) of experimental data. "No screen" shows traces in the absence of an inner pipe. "Open pores" is for a slotted sand screen, whereas "closed pores" is for a blank pipe (no slots). Note that the fast tube wave is least attenuated in the absence of a screen, attenuated in closed pores and substantially absorbed in open pores.

Let us now compare this behavior with the poroelastic reflectivity modeling. Figure 6 shows synthetic seismograms computed for a glass setup. The sand screen is modeled as a poroelastic Biot cylinder. Similar to the experiment with closed pores, we observed two tube waves with the fast tube wave dominating in amplitude. In the presence of a screen with open slots, both waves experienced strong changes. The fast tube wave experienced moderate attenuation and change of waveform.

Figure 6: Synthetic data computed for open and closed pores in the glass setup. (a) Overlay of pressure seismograms for open (red) and closed (black) pores showing that the fast tube wave in a permeable screen experiences attenuation and dispersion. Blue and red lines denote moveout velocities of the fast (1030 m/s) and the slow (280 m/s) tube waves. (b) Slowness-frequency spectrums.

The slow tube wave transformed into a complex packet with weak amplitude. The following physical interpretation can be given to the modeled results. A tube wave is born when the piston-like motion of the fluid inside the pipe creates a radial expansion that is resisted by the elastic pipe. The slow wave is supported mainly by the inner pipe. When this pipe becomes slotted, radial movement of the fluid is no longer resisted since liquid can freely escape to the annulus, thus leading to a strong attenuation of this wave. In contrast, the fast wave is supported mainly by the outer glass solid pipe. In addition, when the inner pipe becomes permeable, a piston-like motion of the fluid in the fast wave can exchange the fluid between the outer and the inner fluid columns, thus creating a moderate attenuation.

The slowness-frequency spectra for open pores (Figure 6b) shows that, similar to the experimental results, the fast wave experiences anomalously high attenuation in the medium frequency range of 350-700 Hz. A more robust display averaging over small, medium and high frequencies is shown on Figure 7. A comparison of Figure 7a and 7b confirms the qualitative agreement between experiment and modeling. In both cases, the fast wave exhibits anomalous amplitude decrease in the medium frequency range, while still preserving higher and lower frequencies. This amplitude decrease should be attributed to anomalous attenuation caused by fluid movement through the slotted porous screen. The frequency range with resonance attenuation is controlled by permeability, i.e., the lower the permeability, the higher the frequency of the band with anomalous attenuation of the fast wave. Therefore, central frequency of the band with anomalous attenuation of the fast tube wave is an additional useful diagnostic of the screen permeability.

Labels: Intelligent well completions, oil gas, real time completion monitoring of deep water wells, Russia, Shell, St Petersburg University

posted by The Rogtec Team @ 16:31  0 Comments