Reservoir Management Under Water Injection A Worldwide Perspective Dr. William M. Cobb Dallas, Texas 2nd National Meeting on Secondary and Assisted Oil Recovery September 8–9, 2005 Malargue, Argentina

Current Oil Production in South America (1000 B/D) Argentina 718 Brazil 1538 Colombia 514 Ecuador 533 Mexico 3252 Venezuela 2640 Total 9150

Argentina Monthly Oil Rate vs Time 1,000 BO

Argentina Year 2004 Production BOPD % of Total Primary Production 442,000 63.2 Secondary Production 257,000 36.8 Total 699,000 100.0

Argentina Monthly Oil Rate vs Time 1,000 BO Secondary Production Primary Production

Argentina Percent Primary & Secondary Production

Argentina Principle Productive Areas . Noroeste Cuyana Neuquina Gulfo San Jorge Austral

Argentina Principle Production Areas Total BOPD % of Country Total Austral 47,000 6.7 Cuyana 41,000 5.9 Gulfo San Jorge 284,000 40.6 Neuquina 310,000 44.4 Noroeste 17,000 2.4 699,000 100.0

Argentina Year 2004 Production BOPD Primary, % Secondary, % Austral 47,000 86.6 13.4 Cuyana 41,000 61.7 38.3 Gulfo San Jorge 284,000 60.6 39.4 Neuquina 310,000 60.5 39.5 Noroeste 17,000 100.0 0.0 Total 699,000

Argentina % of Total Secondary Nequina Gulfo San Jorge Cuyana Austral

Argentina Oil and Injection Well Count vs Time

Argentina Injection Well Count and Average Daily Injection per Well

Argentina Well Distribution on 1/1/05 Producing % of Total Injectors P/I Ratio Austral 289 1.7 40 0.8 7.2 Cuyana 938 5.5 246 4.8 3.8 Gulfo San Jorge 11,005 64.2 2,740 53.6 4.0 Neuquina 4,852 28.3 2,086 40.8 2.3 Noroeste 57 0.3 0.0 - Total 17,141 100.0 5,112 3.4

Daily NYMEX Oil Price Oil Price Gas Price

Common Denominators for Management of Waterfloods on a Worldwide Basis

Why Inject Water? Maintain Reservoir Pressure – Pressure Maintenance Increase Reservoir Pressure – Waterflooding Supplement Natural Water Influx But . . . A, B & C are Displacement Processes and the Goal is to Displace Oil to a Production Well

Worldwide Reminders When Managing Waterflood Activities Pressure Depletion Stops Volumetric Sweep Net Pay Cutoffs Decline Curve Analysis WOR Analysis Waterflood Quarterback Keep the Ax Sharp

Np = Cumulative Waterflood Recovery, BBL. What are the Key Factors that Drive the Outcome of a Water Injection Project? Np ≈ N*EA*EV*ED Np = Cumulative Waterflood Recovery, BBL. N = Oil in Place at Start of Injection, BBL. EA = Areal Sweep Efficiency, Fraction EV = Vertical Sweep Efficiency, Fraction ED = Displacement Efficiency, Fraction

Waterflood Recovery Factor EA = f (Mobility Ratio, Pattern, Directional Permeability, Pressure Distribution, Cumulative Injection & Operations) EV = f (Rock Property variation between different flow units) EVOL = Volumetric Sweep of the Reservoir by Injected Water ED = f (Primary Depletion, Krw & Kro, μo & μw)

Traditional Waterflood Volumetric Sweep Efficiency Calculation Uses Net Cumulative Water Injected (Wi-Wp) Does not Account for Injection losses out of zone Does not Account for Natural Water Influx

Compute Volumetric Sweep Based on Oil Production Data Oil in place at start of waterflooding = Produced oil since the start of injection + Oil currently in reservoir Where: Oil in place at start of waterflood = Produced oil since the start of injection = Oil currently in reservoir = Oil in water bank + oil in oil bank Oil in water bank = Oil in oil bank =

Volumetric Sweep Based on Oil Production Data SPE-38902

Waterflood Statistics Example Waterflood Statistics Conditions at Start of Waterflood Connate Water Saturation = 22 percent Gas Saturation 8 percent Oil Saturation 70 percent Residual Oil Saturation 31 percent Oil Viscosity 0.3 centipoise Oil Formation Volume Factor 1.57 RB/STB

Example (con’t.) Total Unit Pore Volume = 350,000 MB Cumulative Oil Production Since Start of Injection 40,000 MSTB Current Volumetric Sweep Efficiency 0.552 Remaining Oil Production under Current Operations 5,000 MB Estimated Waterflood Ultimate Recovery 45,000 MSTB Ultimate Volumetric Sweep Efficiency under Current Operations 0.600

Volumetric Sweep Efficiency for Waterflood Project (Pore Volume Based on 6.0% Porosity Cutoff) 26.0 MMSTB Cumulative Oil Production = 40.0 MMSTB Remaining Oil Production = 5.0 MMSTB Estimated Ultimate Recovery = 45.0 MMSTB

Volumetric Sweep Efficiency for Waterflood Project (Pore Volume Based on 6.0% and 10.0% Porosity Cutoff) 26.0 MMSTB 8.4 MMSTB 10% Porosity Cutoff 6% Porosity Cutoff Cumulative Oil Production = 40.0 MMSTB Remaining Oil Production = 5.0 MMSTB Estimated Ultimate Recovery = 45.0 MMSTB

What’s the Secret for Maximizing EA and EV (and EVOL)? IT’S THE INJECTION WELL! Properly Locate the Injection Well Develop an Appropriate Pattern! Inject Water where You Find the Oil! Measure and Manage Injection Profiles Keep Fluid Levels in a Pumped Off Condition Balance Injection and Withdrawals Remember the Quarterback!

SHIFTING GEARS

Net Pay Static OOIP Dynamic OOIP Drive Mechanism Controlled by Cutoffs Permeability Distribution between Flow Units (Dykstra-Parson Coefficient) Oil/Water Relative Permeability Mobility Ratio (Oil and Water Viscosity) Fluid Saturations at Start of Injection (So, Sg, Swc) Water Cut Economic Limit

Permeability Cutoff Using the Watercut Method at a 95 Percent Watercut Economic Limit 80 Acre Pattern Dykstra-Parsons, V Sg = 0% Sg = 10% 0.6 0.24 1.10 0.7 0.71 3.30 0.8 1.20 5.60 SPE-48952

CHANGING HORSES

Decline Curve Analysis Assume Gas Fillup has been Achieved (Reservoir contains oil and water Reservoir Pressure is Approximately Constant (Bo is constant) Steady State Flow Prevails (Approximately) Conclusion Water Injection = Liquid Production (at Reservoir Conditions)

Decline Curve Analysis Fact: Conculsion: Oil and Water Production Rates are directly related to injection rates. Therefore, DCA of qo vs t or qo vs Np must be evaluated only after giving consideration to historical and projected water injection rates.

WOR is Independent of Injection Rate Conclusion: WOR is independent of injection rate WOR should be applied to individual wells and not field WOR should be applied using values greater than 2.0

Keep Life Simple

Production Centered 5-Spot Pattern N-Well 80 Acres W-Well E-Well C-Well S-Well

North American Waterflood – Pattern 35-10

North American Waterflood – Pattern 35-10 S-i E-i N-i W-i

North American Waterflood – Pattern 35-10

A Friendly Reminder Waterflood Operations Cartesian Plots of Oil Rate versus Cumulative Oil Production Should Be Prepared on A Well Basis Semi-log Plots of WOR versus Cumulative Oil Production Should Be Prepared on A Well basis Preparation of the Above Two Plots For The Entire Field Gives an Average Result Which May be Optimistic or Pessimistic

Have there been Recent Developments in Waterflooding Technology?? & YES ! ? ? ? ? BUT . . . Improved application of old principles leads to better recovery

What Are the Key Elements of a Successful Waterflood? High Moveable Oil Saturation Moderate to Low Oil Viscosity Favorable Relative Permeability Low Permeability Variation Symmetrical Patterns Ability to Inject Large Volumes of Water Ability to Lift Large Volumes of Produced Water Pumped Off Producing Wells

What are the Pitfalls of Waterflooding Practices? Failure to keep producing wells in pumped off condition Failure to clearly distinguish between Static OOIP and Dynamic OOIP (Primary vs Secondary) Failure to collect sufficient quantity and quality of reservoir data Failure to timely convert oil wells to injection wells Failure to monitor injection water quality Failure to keep the Ax sharp

Summary of New Waterflood Paradigms Remember the Quarterback (The Injector) Keep the End in Mind (Maximize Volumetric Sweep) Keep the Ax Sharp (SPE meetings, SPE-TIGS, and SPE.org provide great opportunities to sharpen the mind!)

Pretty Please with Sugar! Keep Life Simple

Field Analysis – Latin America

Field Analysis – Latin America

Field Analysis – Latin America

Field Analysis – Latin America

Field Analysis – Latin America

Field Analysis – Latin America

Field Analysis – Latin America

Field Analysis – Latin America

Reservoir Management Under Water Injection A Worldwide Perspective Dr. William M. Cobb Dallas, Texas 2nd National Meeting on Secondary and Assisted Oil Recovery September 8–9, 2005 Malargue, Argentina