CO2 FLOODING IN THE MORROW

Based on a workshop co- sponsored by PTTC's North Midcontinent Region, Shell CO₂ Company, Ltd., The University of Kansas, and Mobil Oil, November 17, 1999 in Wichita, Kansas. 

BOTTOM LINE

Miscible CO₂ flooding is a feasible option to help increase oil production from Morrowan reservoirs in western Kansas and Panhandle Oklahoma. There is a significant recovery potential for properly applied projects at a current threshold level of about $15- 20/ barrel oil.

PROBLEM ADDRESSED

Miscible CO₂ flooding has proven to be a viable EOR recovery process when conscientiously applied to Morrowan reservoirs. However, because of Morrow reservoir heterogeneity, detailed CO₂ feasibility and flood design studies should be performed to help determine if a reservoir is a good candidate. Studies from analogous reservoirs should also be consulted. Key sensitivities for Morrow CO₂ flooding include oil price and amount of incremental oil production. The total investment for developing a typical Morrow CO₂ unit (26 million barrels OOIP, 1.3 million barrel recoverable from CO₂ flooding) is estimated at about $2.63 million. Based on current economics and field results from Postle Unit, it is estimated that CO₂ floods in Morrow reservoirs have potential for an additional 50 to 75 million barrels oil.

KEY WORDS:

CO₂ screening criteria, Enhanced oil recovery, Miscible CO₂ flooding, Morrow Formation, Oklahoma Panhandle, WAG injection, Western Kansas

SPEAKERS

CO₂ Flooding Process and Flood Design
Chuck Fox, Shell CO₂ Company Ltd.

Morrow Economics for the Independent Operator
Russell Martin, Shell CO₂ Company Ltd.

Morrow Potential in SW Kansas/ Panhandle OK
Lanny Schoeling, Shell CO₂ Company Ltd.

Update on the Central Kansas CO₂ Project DOE
Alan Byrnes, Kansas Geological Survey

Screening CO₂ Floods in the Morrow Using CO₂ Prophet
Richard Pancake, Tertiary Oil Recovery Project, University of Kansas

Facilities and Subsurface Equipment
Pat Underwood, Mobil Oil

TECHNOLOGY OVERVIEW

Reservoir characterization studies indicate that Morrow reservoirs located in western Kansas and the Oklahoma Panhandle area are heterogeneous. Regional features controlling large- scale Morrowan architecture have resulted in multiple sequences bounded by erosion surfaces. Lower Morrow reservoirs tend to be shoreface sands encased in offshore shales while upper Morrow reservoirs include transgressive incised valley fill (IVF) deposits encased in marine shales. Because each reservoir lithofacies exhibits a unique range of petrophysical properties, careful delineation and mapping of facies is needed for optimum CO₂ flood design and reservoir management. Major lithofacies may be identified by quantitative log analysis.

Why Use CO₂ Flooding in Morrow Reservoirs?
Morrow reservoirs have characteristics that are amenable to waterflooding. Miscible CO₂ flooding is one of the more economical oil recovery processes for recovering additional oil from reservoirs that have been waterflooded. In general, if a reservoir did well during waterflood, a CO₂ flood should also work well. In the Morrow, miscible CO₂ flooding is the only enhanced oil recovery (EOR) process that can recover large amounts of oil. CO₂ offers the lowest Minimum Miscibility Pressure (MMP) and is the most economical solvent available.

Miscible CO₂ Screening Criteria.
Requirements typically include restriction to reservoirs greater than 2,000 ft, with oil gravity greater than 25° API, high residual oil saturations (Sor> 20%), and a reservoir that can pressure up to the MMP. Morrow reservoirs commonly have residual oil saturation between 30- 50%. CO₂ flooding is sensitive to reservoir characteristics such as facies distribution and petrophysical properties. Injectivity must average about 4% of the hydrocarbon pore volume per year. Unfavorable conditions for miscible CO₂ can be created by gravity overrides, reservoir heterogeneity, fracturing and thief zones, asphaltene precipitation, the presence of a gas cap or low waterflood residual oil saturation. Water- alternating- gas (WAG) injection is commonly used to control CO₂ 's tendency toward early breakthrough.

Estimating Morrow CO₂ Flood Performance.
Tertiary miscible CO₂ floods typically have a recovery efficiency of 10- 15% OOIP, and often greater for secondary floods. When OOIP is not known, incremental oil is generally between 20- 30% of the cumulative oil production. Maximum EOR recovery rate is about equal to 1/ 3 the response of peak waterflood oil rate. The net utilization factor (purchased CO₂ ) averages 5 mcf/ bbl incremental oil, with the injection ratios typically two to three times the net.

The CO₂ slug size is generally 40+% of the hydrocarbon pore volume (HCPV), of which about half must be purchased. Typical slug sizes are 20% PV of straight CO₂ , followed by an additional 20% PV of CO₂ with a WAG ratio of 1: 1. Costs can be reduced by reinjecting produced CO₂ . Estimation of the total CO₂ requirement for the flood can be estimated from OOIP, e. g. 25 MMB OOIP results in 2550 BCF CO₂ required.

Operating expenses include CO₂ -related items (purchase, recycling and injection line maintenance) and conventional costs that are related to the maturity status of the waterflood, condition of equipment and incremental operating expenses. For western Kansas and Panhandle Oklahoma, a guideline for estimating costs is $20,000/ inch diameter/ mile plus $150,000 for CO₂ trunkline; workover of producers is $40,000/ well; equipping CO₂ injectors is $60,000/ well; surface facilities cost about $22,000/ injector plus $10,000/ producer; and CO₂ recycle compression costs are $0.38/ mcf.

Facilities And Subsurface Equipment.
Morrow CO₂ flood surface facilities include the production wellhead tree, production flowlines, injection wellhead tree, injection lines, 3 phase testers, heater treaters, gas processing, and injection facilities. Production flowlines need to be designed to handle the anticipated peak volume, pressures and temperatures of the produced fluids. Because of corrosion problems, production (and injection) lines must be made of a CO₂ -compatible material and the lines should be monitored. New lines for CO₂ injection should be installed, but existing lines for water can continue to be used. Injection lines should be large enough to deal with anticipated water and CO₂ volumes. Recommended additional needs for CO₂ floods include a CO₂ analyzer, a Model E Echometer/ Nabla Ventawave, and a chemical program to anticipate and handle corrosion, paraffin, and water quality problems.

Key Morrow Economic Sensitivities.
Economic case studies indicate that key sensitivities for Morrow CO₂ flooding include oil price and amount of incremental oil production. Economics are less sensitive to the financial investment in the flood and the price of CO₂.

Based on assumptions of a typical field with about 26 million Bbls OOIP, about 1.3 million Bbls of CO₂ -produced oil, 5.4 BCF CO₂ purchased, with 7 injection wells and 14 CO₂ producers, the total investment for drilling 4 new wells, workovers, other equipment, and building 10- 12 miles of pipeline total is estimated at $2.63 million. Economic constraints on this estimated cost include oil price in the range $16.00- 20.00 per bbl, 15 cent/ Mcf tariff on existing pipelines, 38 cent/ Mcf compression cost, $27,500/ yr. operating cost per well, no EOR tax credits and a royalty burden of 12%.

CO₂ Flood in Postle "Morrow" Field, OK.
Postle Field reservoir parameters include: depth 6,100 ft, sand thickness 25 ft, porosity 17%, permeability 47 mD, initial oil saturation 70%, reservoir temperature 140° F, original reservoir pressure 1,630 psi, reservoir pressure at startup of CO₂ flood 2,750 psi, minimum miscibility pressure 2,100 psi, oil gravity 40 oAPI, oil viscosity 1.2 cp, original Formation Volume Factor 1.28, OOIP 265 MMSTB.

In the Postle Field, CO₂ first response occurred about six months after flood inception. The field had CO₂ breakthrough in one year with 10% pore volume injected before significant response. Production has risen from about 2,500 BOPD in 1996 to more than 6,500 BOPD in late 1999, with a targeted peak response of 13,000- 15,000 BOPD. The field exhibits a higher than expected CO₂ retention. Estimated oil production from CO₂ injection is currently 3.8 MMSTB with an estimated ultimate oil production of 25 MMSTB.

CONNECTIONS:

Chuck Fox, Kinder Morgan CO₂ Company, L. P.
500 Dallas, Suite 100, One Allen Center
Houston, TX 77002,
Phone 713- 369- 919, Fax: 713- 369- 9195, Email charles_fox@kindermorgan.com

Russell Martin, Kinder Morgan CO₂ Company, L. P.
500 Dallas, Suite 100, One Allen Center,
Houston, TX 77002,
Phone 713- 369- 9169, Fax: 713- 369- 9195, Email russell_martin@kindermorgan.com

Lanny Schoeling, Kinder Morgan CO₂ Company, L. P.
500 Dallas, Suite 100, One Allen Center,
Houston, TX 77002,
Phone 713- 369- 9113, Fax 713- 369- 9195, Email Lanny_Schoeling@kindermorgan.com

Pat Underwood, Mobil Oil,
396 W. Greens Road
Houston, TX 77067,
Phone 713- 431- 1328, Fax 713- 431- 1540, Email pat_c_underwood@email.mobil.com

Alan Byrnes, Kansas Geological Survey
1930 Constant Ave.,
Lawrence, KS 66047
Phone 785- 864- 2071, Fax 785- 864- 5317, Email abyrnes@kgs.ukans.edu

Richard Pancake, Tertiary Oil Recovery Project
4008 Learned Hall, Lawrence, KS 66045
Phone 785- 864- 4491, Fax 785- 864- 4967, Email pancsake@ukans.edu

For information on PTTC’s North Midcontinent Region and its activities contact:
Rodney Reynolds, Project Manager,
Energy Research Center, and Petroleum Engineer Tertiary Oil Recovery Project, University of Kansas
1930 Constant Ave., Lawrence, KS 66047
Phone 785- 864- 7398, Fax 785- 864- 7399, E- mail reynolds@cpe.engr.ukans.edu

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