Use of steam assisted gravity drainage with oxygen ("sagdox") in the recovery of bitumen in thin pay zones

Abstract

A SAGDOX process to recover liquid hydrocarbons from at least one thin pay zone in a hydrocarbon bitumen reservoir, via a substantially horizontal production well, where the hydrocarbon bitumen reservoir has a top and a bottom. The process includes:i) Injecting steam into the hydrocarbon bitumen reservoir above the substantially horizontal production well;ii) Injecting oxygen into the hydrocarbon bitumen reservoir above the substantially horizontal production well;iii) Recovering liquid hydrocarbon gravity drainage into the substantially horizontal production well.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. application Ser. No. 14 / 058,488, filed on Oct. 21, 2013, which claims benefit of U.S. Application Ser. No. 61 / 717, 267, filed on Oct. 23, 2012 and is a CIP of U.S. application Ser. No. 13 / 543,012, filed on Jul. 6, 2012, which claims benefit of U.S. Application Ser. No. 61 / 507,196, filed on Jul. 13, 2011. U.S. application Ser. No. 14 / 058,488 is also a CIP of U.S. application Ser. No. 13 / 628,164, filed on Sep. 27, 2012, which claims benefit of U.S. Application Ser. No. 61 / 549,770, filed on Oct. 21, 2011 and is a CIP of U.S. application Ser. No. 13 / 543,012, filed on Jul. 6, 2012. U.S. application Ser. No. 14 / 058,488 is also a CIP of U.S. application Ser. No. 13 / 628,178, filed on Sep. 27, 2012, which claims benefit of U.S. Application Ser. No. 61 / 550,479, filed on Oct. 24, 2011. U.S. application Ser. No, 14 / 058,488 is also a CIP of U.S. application Ser. No. 13 / 888,874, filed on May 7, 2013, which cla...

AI Technical Summary

Benefits of technology

This patent aims to optimize the ratio of oxygen to steam during a process to maximize the effectiveness of the process. The patent suggests increasing the ratio of oxygen to steam during the process, specifically towards the end of the process, to achieve the highest ratio possible. This may improve the efficiency of the process and lead to better results.

Problems solved by technology

Increased pressure increases bitumen productivity but harms process efficiency (increases SOR).

Despite becoming the dominant thermal EOR process, SAGD has some limitations and detractions.

If the reservoir is highly slanted, a horizontal production well will strand a significant resource.

SAGD cannot work on heavy (or light) oils with some mobility at reservoir conditions.

By definition, the heat energy in saturated steam is not high enough quality (temperature) to vaporize water.

Field experience also shows that heated connate water is not mobilized sufficiently to be produced in SAGD.

This makes it difficult for SAGD to breach or utilize lean zone resources.(5) The existence of an active water zone—either top water, bottom water, or an interspersed lean zone within the pay zone—can cause operations difficulties for SAGD or ultimately can cause project failures (Nexen Inc., “Second Quarter Results”, Aug. 4, 2011) (Vanderklippe, N., “Long Lake Project Hits Sticky Patch”, CTV, 2011).

If the reservoir is “leaky”, as pressure is increased beyond native hydrostatic pressures, the SAGD process can lose water or steam to zones outside the SAGD steam chamber.

If liquids are lost, the WRR decreases and the process requires significant water make-up volumes.

Ultimately, if pressures are too high, if the reservoir is shallow and if the high pressure is retained for too long, a surface break through of steam, sand and water can occur (Roche, P., “Beyond Steam”, New Tech. Mag., September 2011).(7) Steam costs are considerable.

Assuming SOR=3, WRR=1 and a 90% yield of produced water treatment (i.e. recycle), a typical SAGD water use is 0.3 bbls of makeup water per bbl of bitumen produced.(9) SAGD process efficiency is “poor” and CO2 emissions are significant.

If one is close to the surface, it becomes too risky to operate SAGD at overpressures.

But, no reservoir is truly homogeneous.

Thin pay deposits will have increased losses to overburden because the steam interface will hit the ceiling quicker than for thick pay resources.

Even when productivity is reduced, accounting for reduced gravity heads, thin pay production may only last for a few years compared to over 10 years for thicker pay resources.SAGD is sensitive to reservoir impairments (shales, lean zones .

If these impairments are proportionately more prevalent in thin pay reservoirs, SAGD will have problems as discussed herein.Heat losses can reduce process of efficiency.

But, the process has the following deficiencies:The operating temperature is lower than SAGD at the same P, because steam is diluted by solvent gas.

. . ) is very costly (more valuable than bitumen).

However, the process has the following deficiencies:Capital expense is similar to SAGD.

But this pure solvent process has the following deficiencies:The processes have been proven in field tests to be difficult (slow) to start.Productivity has been much less than SAGD.Solvents are expensive (more costly than bitumen), so that, even with modest losses, operating expenses are a concern.The processes are 2D, without longitudinal flows in the reservoir.Focus has shifted to heavy oils (with some initial injectivity) not to bitumen.Solvent losses (to the reservoir) are a key economic concern.

Heat losses from the steam injector to the produced fluids can be considerable for uninsulated, concentric, carbon steel tubing.

The use of a steam trap (sub cool) control for production rates will be difficult, at best.

Even for heavy oil deposits with some steam injectivity and some primary production, start up was difficult and protracted (Elliot (1999)).

Initial production rates were disappointing (Elliot (1999)).

Initial steam quality at the sand face was poor due to heat losses to produced fluids.

Because of these issues, an alternative start-up procedure using cyclic steam has been suggested (Elliot (1999)), but this has not been field tested.Even after start-up, SWSAGD performance has been disappointing (Saltuklaroglu (1999), Elliot (1999)).

Hard to breach barriers.Solvent is costly (more valuable than bitumen).

Solvent losses are a key economic concern.Solvent losses cannot be confirmed or estimated prior to end of process when solvent inventory recovery is attempted.Productivity may be worse than SAGD.Poor field test results for VAPEX—a similar process (NSolv, “Developing an In Situ Process .

Recently, Petrobank's reserves consultant dropped reserves related to THAI because of protracted poor performance (Energy Inc, “Petrobank suffers setback with THAI”.

Mar. 8, 2012).One of the problems with THAI is how to prevent air from short-circuiting the process and by-passing the reservoir by entering the production well upstream of the combustion front (FIG. 22).

Either of these is a difficult task.Another issue is that lateral growth can be slow.

This can impair liquid production rates.The field experience for THAI is poor (Calgary Herald, “Petrobank Technology earns Zero Grade”, 2012).The current focus of THAI is on heavy oils, not bitumen (OGJ (2012))(viii) Another, related combustion process is Combustion Overhead Gravity Drainage (COGD) also called Combustion Overhead Split Horizontal (COSH) (FIG. 23).

The flank gas removal system promotes lateral growth—a problem for THAI.

But by problems include high costs of steam and lack of field tests.But once communication is established between the injector well 6 and the producer well 8, there is little pressure differential to push oil to the producer well, without significant steam breakthrough to the production well.

ISC is a process that so far, has shown little application for bitumen recovery.

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