SAGD

SAGD

By Luis Gomes

Reservoir Engineering III

Summary

SAGD (steam-assisted gravity segregation) is one of the technologies used in Canada, since its founder Dr. Roger Butler implemented in 1978, it is based on two parallel horizontal wells each other and one above the other, which seeks improve the oil viscosity and therefore the mobility of it, over the years has been modified SAGD, but always with the same principle to generate the steam chamber where you change the properties of oil, with some limitations as a relation of permeability, thickness of the producing sand, depth, and other constraints that make a simple principle that assisted gravity segregation is an engineering challenge. In Venezuela, the pilot project took place in the Tia Juana Field in 1987, where the results were very positive, both for the effectiveness of simulation and execution in the fields of Venezuela, showing what can be efficient , recovery factors as desired by almost 60% can be obtained with a well-planned interdisciplinary work.

Introduction

The world we live each day grows more on their energy needs, and this negative slope reflects the global reserves of oil, give us a framework in which the heavy oil business becomes stronger, the economic aspect is obviously implicit in all processes, projects and political agreements that lead to the improvement or application of new technologies for extraction of these raw increasingly requested, but at the same time more efforts in all areas where these involved the extraction of crude oil found in these unconventional reservoirs.

These technologies basically strive to increase oil mobility and reduce its viscosity, so this document deals with one of them, the Steam Assisted Gravity Drainage (SAGD by its English acronym), which was designed by Roger Butler as a specific distribution of wells and each has a specific function (injector and producer), the success of this method has brought about significant improvements in recoveries and in turn its development, with new releases, improvements in properties of fields, positions of wells, increased security, more insulating liners, among other issues mentioned below to better understand the benefits and limitations of SAGD.

Fundamentals of Technology:

The history of SAGD (steam-assisted gravity segregation) begins in Canada since its founder Dr. Roger Butler implemented in 1978, the success of this technology in heavy oil fields was remarkable, ie the energy expenditure is lower compared with other processes as well with better re recovery factors. In Venezuela, the first pilot test was applied in 1997 in the Tia Juana field located in the West Country. At that time the production had unexpected results (700Bbl/día), after 5 years of development was obtained 50% recovery factor, giving a global endorsement of the importance of the application of SAGD as recovery method for crude heavy.

Among the SAGD thermal recovery processes is one of the best known and developed with other variants, since it has yielded important results.

SAGD basically consists of penetrating the ground with two parallel horizontal wells each, located one above the other with a vertical distance of 5 m. [Fig 1], initially steam is injected into both wells in order to generate an energy transfer to the oil formation and increasing the temperature of oil in all the surroundings of the wells when the reservoir has a warm, gives way to the next phase, steam injection is stopped only in the lower well at this point the call is created steam chamber where steam condensation occurs on the periphery of the camera. The latent heat released by the steam is transferred to the formation mainly by conduction, ie steam injection heating fluids achieved on site by direct contact with steam. By contrast, the displaced fluid is heated by conduction and convection, for this reason the flow of condensate (hot water) and oil occurs in the direction perpendicular to the direction of heat flow by conduction [Fig 2], that aims to reduce oil viscosity and increase their mobility, which attracts such a facility greater positive impact on the extraction of oil.

Therefore the lower well will produce feature, while the top is responsible for injecting steam. It is important to note that operationally we inject steam at a pressure lower than the fracture pressure of the reservoir, to prevent damage to the training that contribute to the decrease in porosity or interfere with heat transfer. It should be added that as this process is applied, the producing well is closed periodically to avoid creating a steam cycle, it is the extent of the possible, not to produce the injected steam.

AWSC application window:

The following table gives a short summary of the ideal conditions for the application of SAGD.

2000 cp.">Depth <> 2000 cp.

2000 cp."> 1000 mD">Horizontal permeability> 1000 mD

1000 mD"> 100 mD">Vertical permeability> 100 mD

100 mD">Gas layer <= Low clay content <= Low Fracturing None. 49 pies.">Water Oil Ratio <> 49 feet.

49 pies."> 0.26">Porosity> 0.26

0.26">

0.26">In detail:

• The sites should have at least 10% of clays, because these are swollen by absorbing water that was to Countess of steam.

• The associated aquifers should be treated with care as they are not to the steam comes into contact with an aquifer, part of the injected steam is lost due to high water permeability.

• The presence of a thin layer of gas can prevent loss of heat to the overlying layers of the site due to the low thermal conductivity of the gas layer. For this reason, a thin layer of vapor can not be a negative aspect in the application of SAGD.

• Small-scale fractures may be beneficial to distribute the steam in the viscous oil, and in turn add a heat transfer and mass more efficiently.

For prospective sites where you want to apply this technology, have optimal effectiveness is necessary to take into account these factors not mentioned.

or stacked Arena (river or sea) without significant barriers in the sand shale. The presence of a good caprock at the top of the sand is important for the confinement of the vapor.

or units of large and continuous flow.

or sand with high permeability ratio (kh / kv).

So the prospects are not attractive for SAGD who meet the following factors:

Thickness of sand or smaller than 5 m.

or regions with large layers of gas or water in the background.

Arenas with multiple insertions or shale.

or regions with significant and unpredictable changes of facies between sand and shale.

or regions with reported fractures, faults.

or areas where the controlled confinement of the steam chamber is difficult.

Case Study

SAGD, Pilot Test in western Venezuela. Tia Juana field.

The area selected for the pilot was the field Tia Juana (1997), in western Venezuela [Fig3] contains heavy oil (9-11 ° API) with a relatively high viscosity (from 10.000 to 45.000 cp. To 110 ° F) that has historically demonstrated low recoveries in the order of 10% with the use of cyclic steam stimulation ( CCS). The CCS process has been effective in some parts of the Tia Juana field, but in the northern part of the field where the viscosity is higher, the CCS as a process of recovery has shown a lower efficiency. The low recovery obtained, together with long CCS process and the problems associated with the production of viscous oil, gave a strong step for the SAGD which is used as aforesaid parallel horizontal wells one above the other and can operate at the high scan rates.

The deposits in the Tia Juana field produced in the Lagunillas Formation. The reservoir is composed of channels, with the top of the reservoir ranging from 450 to 1000 feet.The total thickness of the bottom of the Lagunillas formation averages 280 feet and is divided into two main layers. The top layer of 40-85ft. Which was selected for the pilot because of the condition of homogeneity of the rock (99% quartz).

In this project we decided to drill two pairs (LSE 5085-5088 and 5091-5092) in parallel as shown in [Fig 4], this decision was based on the performance of the good production of LSE 4703 near the pilot area. The wells were drilled in the experience of pilot wells in Canada with a distance of 5 meters vertically, one drilled with conventional directional tool and the other with the MGT with traces of magnetic data.

The first pair (LSE 5085-5088) was completed with 6 conventional thermocouples in the heel, middle and end of the horizontal sections. A capillary is installed in the heel and toe of the wells to monitor the pressure at the same time. The second pair also completed a fiber optic system for measuring temperature in the well profile in real time.This technology was chosen in part to evaluate the technology itself but also to enable the monitoring of steam in the producing well and the progressive growth of the steam chamber.

Reservoir parameters were as follows after the simulation:

The residual oil saturation 10%

Initial temperature 100 ° F

Well spacing of 328 ft

Soi 85%

Swi 15%

Effective permeability. 1.5 D

Value Kv / Kh 0.43

Vertical thickness between wells 30 ft

After collecting the data and completing the wells were implemented the pilot project beginning in 1997, and as they were reviewing production rates comparisons were made with the simulation, which initially collated, ie it had an estimated 300 Bbl / day, but after generating the steam chamber and produce it reached a peak of 700 Bbl / day as shown in Figure 5, but in time it looks like the simulation and the real cup takes almost same positive values as the estimates given by the interdisciplinary group formed by PDVSA, Dr R Butler, Mr C. and Bohm.

Expected recoveries:

The process resulted in recovery factors in the order of 52 and 60%, higher values for heavy crudes.

Associated costs:

Estimates of this process and exhibits displayed by the operating companies and PDVSA for SAGD costs, focus very well with the energy ratio and energy used by the oil extracted, ie the energy balances for these processes are fundamental, reducing costsheat loss, almost perfect completions with high quality and high-capacity cement it to retain heat and so this does not come to training, the distances between the Steam Generators and holes can not be larger than 1.2 km if it exceeds this value is possible to lose almost 20% of the energy used. That would give significant long term value in relation to the energy used in connection with the backlog of hydrocarbons.

Conclusions:

1 - The SAGD pilot was successfully implemented in the Tia Juana field after year.

2 - initial production rate was better than expected (700-vs-300 BPD), but long-term real output tends to coincide with the analysis and numerical simulations.

3 - The final recovery with an order of 52 and 60% for the simulation which means an increase ultimate recovery by more than 40% compared to CCS.

4 - The injection of steam required to maintain production is 120 -140 T / D. This is close to 70% less steam than expected spending other processes.

5 - After 3 ½ years of simulation, the optimum injection rate is approximately 120 to 140 T / D and production of oil was not greatly affected by rising rates of steam injection

6 - It is necessary to implement heat exchangers and reducing the distances of the steam generators with respect to the wells, in order to reduce energy costs.

7 - The implementation of technologies derived from X-SAGD SAGD as seeking a different arrangement, leaving behind applying parallelism and perpendicularity with more wells and not just a couple, or SW-SAGD seeking to implement an operational savings of only a well injector and producer is at a time. This is what the planet needs to find ever greater recovery factors at lower cost.

References

SPE 53687-MS, “SAGD, Pilot Test in Venezuela” Humberto A. Mendoza, Jose J. Finol, PDVSA; Roger M. Butler, GravDrain Inc.

MAGDALENA PARÍS DE FERRER. “Inyección de Agua y Gas en Yacimientos petrolíferos” Segunda Edición.

ING DIEGO MAFRE J. “Optimización del proceso X-SAGD en un área con características representativas de la Faja del Orinoco aplicando técnicas de diseño experimental” UCV, (2009).

LAKE. “Enhanced Oil Recovery”, Prentice Hall, USA (1989).

SCHLUMBERGER “Oilfield Review” Otoño de 2006 pp 43-46

C.V. Deutsch y J.A. McLennan “Guide to SAGD (Steam Assisted Gravity Drainage) Reservoir Characterization Using Geostatistics” Centre for Computational Geostatistics (2005).

SPE 54009, “Mechanical and Thermal Properties of Unconsolidated Sands and Its Applications to the Heavy Oil SAGD Project in the Tia Juana Field, Venezuela”

SPE 121489 “Energy Balance in Steam Injection Projects Integrating Surface-Reservoir Systems Author E. Valbuena, J.L. Bashbush, and A. Rincon, Schlumberger”

Fig. 1- Esquema de ubicación de pozos en SAGD.