Latest Oil and Gas News Russia

Oil & Gas News

Wednesday, 27 May 2009

Heavy Oil Recovery; Cyclical Solvent Injection, CSI

Jose Alvarez and Roy Coates
Alberta Research Council

Canadian Heavy Oil Resources
The Western Canadian Sedimentary Basin (WCSB) contains as much as 30 billion barrels of heavy oil in place (OIP). Approximately two thirds of these resources, 19 billion barrels, are located in the heavy oil reservoirs of the Lloydminster area. Therefore, the Lloydminster area, located on the Alberta-Saskatchewan border, has a strategic importance for the energy sector in Canada as heavy oil production accounts for almost 20% of the total Canadian oil production.

The Lloydminster reservoirs are characterized by being very fine to fine grained relatively clean quartz unconsolidated sand bodies with porosities ranging from 29 to 35%. These relatively shallow reservoirs, 500 to 600 m deep, have temperatures around 22 0C and permeability values varying from 100 to 5,000 md. The oil gravity ranges from 13 to 17 0API and dead oil viscosities can be as high as 40,000 mPa.s. Additionally, around 80% of the OIP is found in formations that are less than 5 m thick, which leads to additional exploitation challenges.

Primary Production
Primary production, conventional or unconventional (cold heavy oil production with sand, CHOPS), in the Lloydminster area has been under way for about 60 years and is the technology applied by most of the Canadian heavy oil producers. Recovery factors are in the order of 8 to 15% OOIP. Cold Production takes the advantage of specialized pumping equipment, e.g. progressive cavity (PC) pumps, in order to deliberately produce sand along with the reservoir fluids. The production of sand creates long channels or wormholes with high permeability. Evidence suggests that some wormholes may grow as far as 200 m from the production well. The combination of foamy oil behavior and the high permeability channels accounts for the high recovery factors and high production rates encountered in most of the Lloydminster's reservoirs.

In spite of the commercial success of cold production, there are several indicators that suggest it may be reaching a plateau. Actual production is estimated to be 36,500 m3/d (230,000 bbl/d) and production forecasts are showing a 50% decline over the next decade. Several factors are contributing to this production decline:

  • Industry is running out of new sites for cold production
  • Watering out of wells due to water encroachment through wormhole systems
  • Pressure depletion and reduced drive energy
  • Low liquid inflow and high producing GOR
  • Wells do not last more than 7 to 8 years due to above reasons

Therefore, the future of these reservoirs depends on the development of post-cold production technologies to tackle the remaining 85% to 90% of OOIP.

Post-Cold Production Technologies
Evaluation of follow up processes for mature cold production reservoirs has been a research topic for the last 15 years in Western Canada. Thermal and non thermal processes have been investigated at laboratory scale using reservoir properties representative of Lloydminster reservoirs. The aim of the research has been the development of an economically viable IOR process which utilizes the existing wells and wormhole networks to provide access for injection of stimulation fluids into the formation. The injected fluids reenergize the formation, supply drive energy and correct mobility imbalances through viscosity reduction and phase redistribution.

The experiments are performed in a radial drainage apparatus, representing a segment of the reservoir draining into a 6 cm diameter wormhole located in the middle of 6 m thick pay zone. The assumption for this configuration is that once the wormhole is created, the mechanisms controlling fluid production generally affect the flow of fluids between the reservoir and the wormhole, and that this flow is in a radial direction. The model is 3 m in length, with a 1 cm internal diameter at the bottom and a 12 cm internal diameter at the top.

More than 15 experiments were performed in the radial drainage apparatus evaluating thermal and non-thermal follow-up processes.

Thermal Processes
Economical analysis, based on simulation results, indicated that cyclic steam stimulation (CSS) has more potential to be economic in thicker reservoirs, i.e. pay zones greater than 15 m. This observation is in line with that reported from field experiences in thin pay zones of Lloydminster, where high heat losses have produced uneconomic outcomes. These results rule out thermal processes for more than 80% of the Lloydminster reservoirs.

Non-Thermal Processes
In the cyclic solvent injection concept (CSI), a solvent mixture is injected in the reservoir, followed by a soak period and a production period, analogous to the CSS process. As a rule of thumb, the solvent mixtures to be used in the CSI process should be predominantly gaseous to replace the voidage created by primary production, have good solubility in oil, be readily available and be relatively inexpensive. With those requirements in mind several solvent mixtures have been evaluated. These mixtures consist of an inexpensive carrier gas such as methane or carbon dioxide, enriched by propane or butane. The mixtures compositions were selected such that for the experimental pressure range, they were either in the gas phase region, close to the dew point or in the two phase region. Operational conditions, such as number of cycles, soak time, solvent loading, comingled or slug injection strategies, are key in this process and should be evaluated in physical and numerical models before testing the CSI technology in the field.

The figure shown below compares the recovery factor between methane based mixtures and carbon dioxide based mixtures with propane. Carbon dioxide based mixtures have two to three times higher recovery factors than the ones obtained by methane based mixtures. Higher oil swelling, higher dissolution and greater viscosity reduction with carbon dioxide can be responsible for the higher oil recovery. Additionally, associated experiments carried out to examine exsolution behavior of different solvents from heavy oil, have reported abnormally high supersaturation of carbon dioxide. This behavior may be the key to the additional recovery obtained with carbon dioxide mixtures. Further investigations are ongoing.

CSI Pilot Tests
Husky Inc. is operating the Edam field in the Lloydminster area. A blend of methane-propane began to be injected in June 2006. Injection and production were cycled between two unconsolidated-sands formations. One of the formations is 7 m thick, containing 12 0API oil with a viscosity of 15,000 mPa.s. The other formation is thinner, 3.5 m of pay, containing a more viscous oil, 27,000 mPa.s and 110API. The thicker formation had average oil recovery during cold production but little water production. The other formation produced above average water and oil during the cold production. The reported information for this pilot indicates that the results have been encouraging and therefore the operator will continue evaluating CSI operational strategies in this field.

For More Information, Contact

Jose Alvarez, Ph.D
Solvent Strategic Area Leader,
Heavy Oil & Oil Sands,
Alberta Research Council,
Edmonton, Alberta, Canada,
T6N 1E4
Phone (780) 450-5395

Roy Coates, P. Eng
Reservoir Engineer Manager,
Heavy Oil & Oil Sands,
Alberta Research Council,
Edmonton, Alberta, Canada,
T6N 1E4
Phone (780) 450-5261

Labels: , , , , , ,

posted by The Rogtec Team @ 16:22 


Blogger Jane Zhi said...

Have you considered to use viscosity reducer for heavy oil production?

31 March 2010 01:45  

Post a Comment

<< Home

Latest News: