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Outline Waterflood design life and injection efficiency Conformance management Injection well design Waterflood surveillance Water quality Fracturing and subsurface integrity Interdisciplinary aspects of waterflooding

Waterflooding: The Gateway to Enhanced Oil Recovery

Waterflood Mobility Ratio Mwf = mo krw/mw kro Mwf > 1 is unfavorable – water is more mobile than oil Mwf < 1 is favorable – oil is more mobile than water

What is the Design Life of Your Waterflood? Design Life affected by: Mobility ratio Pore volumes injected (PVI) per year Injection efficiency Water quality Permeability Well spacing Onshore versus offshore

Case History: Pore Volumes Injected for Four Offshore Reservoirs

How Efficiently Is Your Water Injection Displacing Oil? Technique is based upon net accumulated water in the reservoir Projects with good injection confinement will be close to 100% efficiency (actual = theoretical) Injection efficiency impacts overall water requirements and facility life Field example to right lacks confinement and has ~75% efficiency

Voidage Replacement Ratio (VRR) VRR is used as a leading indicator to achieve target reservoir pressure (particularly when bottom hole pressure data is not available) Also known as FIFO (fluid-in fluid-out) or IWR (injection-withdrawal ratio) Provides accounting of reservoir barrels into and out of the reservoir Waterfloods should have a target, minimum, & maximum reservoir pressures

Typical VRR Values After Fill-up

Management of Layered Waterflood Response

Waterflood Analysis Techniques Identifying Injector-Producer Relationships Lorenz coefficient – Dykstra-Parsons Capacitance-resistance models (CRM) Streamtube or streamlines Electromagnetic surveys Gravimetric surveys

Injector Completions for Conformance Control

Elements of a Waterflood Surveillance Plan Required Routine Surveillance : Production testing Injection measurement Water quality Surface & bottomhole pressures Production and injection logging Well mechanical integrity

Cross-functional Waterflood Management

Typical Water Quality Specifications

Offshore Water Injection Plant Scorecard

Biofouling: Consequences of Not Meeting Water Quality Specifications? What are Biofilms? They are collections of microorganisms and the extracellular polymers they secrete. They attach to either inert or living substrates. These bacteria are classified as planktonic (free floating) or sessile (anchored).

Under Deposit Corrosion: Consequences of Not Meeting Water Quality Specifications?

Oxygen: Consequences of Not Meeting Water Quality Specifications?

Water Injection Plant (WIP) Operations Are your water injection plant operations lower priority relative to oil & gas plant operations? Operations staff in a difficult position: Do they meet a water volume target or a water quality specification? Cross functional discussion is required to make the best decision for overall waterflood management.

Operational Discipline with Water Quality Do you have a water quality specification or a water quality suggestion? Do you have quality criteria for stopping water injection? The negative impacts of off-spec water are not reversed with pigging, acidizing, chemical shock treatments, surface piping replacement, etc.

Matrix Injection Myth in Waterfloods Long term matrix injection cannot be achieved with practical water quality levels in sandstone reservoirs. Some near wellbore fracturing will occur in most injectors due to thermal stress & plugging effects. Injection pressures, rates and water quality can be used to manage fracture geometry. Vuggy, fractured carbonates can be an exception

Subsurface Integrity Management for Waterfloods Subsurface integrity management ensures injected fluids are confined to targeted and permitted reservoirs. Industry events with injection water breaching seabed or earth’s surface Increasing societal and governmental concerns Historical focus has been on understanding reservoir fracturing and not the overburden and caprock. Keeping injection pressures below caprock fracture pressures does not guarantee containment – geomechanical modeling may be required.

Key Takeaways Understand the design life and processing rate of your reservoir (PVI/year) Understand how much of your water injection is effective Plan for early water breakthrough and layered reservoir management Understand surveillance minimums and emerging fiber optic technologies Use operational discipline with your water quality, have criteria for stopping injection , know your water chemistry Plan for injector fracturing and subsurface integrity management Use a cross functional/interdisciplinary team approach