Objectives. Describing Waterflooding. Infill Drilling. Reservoir Life Cycle

Transcription

1 Objectives Describing Waterflooding Definition Objectives Candidates Patterns Oil, water, and gas saturations Fractional flow Performance measures Practices and problems Reservoir monitoring 1 2 Reservoir Life Cycle Infill Drilling 3 4

2 Infill Drilling Waterflooding Injection of water into a reservoir Increases reservoir energy Sweeps oil towards producing wells Most widely applied secondary recovery method Accounts for about 50% of U.S. oil production 5 6 History of Waterflooding ~ ~ History Goal of of Waterflooding Waterflooding * First recorded waterflood in Pennsylvania. Waterflood projects in Oklahoma and Texas The primary goal of waterflooding is to displace oil with water in an efficient manner that maximizes the profitable recovery of oil from a reservoir. Widescale waterflood implementation Infill drilling Tertiary recovery 7 8

3 History of Waterflooding Waterflooding increases the amount of oil recovered from a reservoir in two ways. Pressure maintenance (Maintain high well productivity) Displacement of oil with water Reasons for Water Injection Pressure Maintenance Maintain pressure above the bubble point to prevent: 1. Gas breakout which reduce shrinkage factor and maintain oil of low viscosity 2. Relative permeability: Gas saturation increases 3. IPR? Water Drive Push water towards the production wells, usually done when peripheral wells cease to be productive Shift water from low permeability regions 9 10 Pressure Maintenance Gas Displace Oil With Water Water Treatment Plant Production Well Oil Sealing Fault Useinjectorproducerpatternstosweepoilfromthe reservoir. Primary recovery not very efficient. Waterflooding yields additional production. Water Injection 11 12

4 Primary Drive Mechanisms Most applicable: Solution-gas drive Gas-cap drive Weak water drive Not applicable Strongwaterdrive Primary Drive Mechanisms Solution-gas drive reservoirs are some of the best candidates for waterflooding. Gas-cap drives benefit from waterflooding but require careful attention to prevent 1) water injection losses into the gas cap 2) oil being pushed up into the gas cap. A weak water drive that cannot maintain reservoir pressure can be supplemented by water injection. Strong water drive reservoirs generally do not need any water injection. Proposed and Conditions of Gas and Water Injection Advantage: 1- Readily available at low cost (economics) 2- Recovery efficiency of the water flood process is generally high because of the favorable mobility ratio, 3- Most reservoir rocks are water wet Water entry into the smaller pores. Effective permeability to water is lower 15 16

5 Proposed and Conditions of Gas and Water Injection 5- Pumping of water to increase injection pressure above the hydraulic head is relatively inexpensive. 6- Water formation volume factor is about one. Hence, volume of water required to replace reservoir voidage is relative low. 7- Spreads well throughout the formation Proposed and Conditions of Gas and Water Injection Disadvantages: 1- Scaling in wellbores and facilities due to water incompatibility. 2- Injection well plugging due to suspended solids and entrapped oil. 3- Corrosion in wellbores and surface facilities. 4- Production, handling, separation, and disposal of produced water A typical water flood project The essential components of a water flood project, described below: 1- Water source and its treatment sufficiency, treatment, compatibility, transport to the injectors 2- Water injectors Pressure rating, mechanical integrity, injector/reservoir connectivity, 3- Reservoir Reservoir characteristics, fluid distribution and saturations, and reservoir/producer connectivity. 4- Producers Pressure rating, mechanical integrity, Reservoir monitoring 5- Water oil separation / water conditioning plants Size, efficiency of oil separation, efficiency of disposal water conditioning 6- Disposal wells Aquifer or reservoir characteristics, injection pressure rating, and safety / environmental related concerns. A Typical Water Flood Project 20

6 Source Waters Seawater 3.5% salinity ph Oxygen saturated High in bacteria Aquifer Water Salinity from 1,000 to 300,000 ppm May contain carbon dioxide and/or hydrogen sulphide ph acidic Oxygen free Free of bacteria (usually) Produced Water Will need to be supplemented for pressure maintenance May contain carbon dioxide and/or hydrogen sulphide ph acidic Oxygen free Main Sources of Injection Water 1- Shallow aquifers, particularly if their waters cannot be used for domestic or agricultural consumption - Amounts of dissolved salts i. Formation fines ii. Precipitation products iii. Corrosion products iv. Bacteria / algae products Main Sources of Injection Water 2- Surface water from a lake, river, or sea - Amounts of dissolved salts - Amount of dissolved gases i. Oxygen ii. Carbon dioxide iii. Hydrogen sulfide - Quantity and nature of suspended solids Injection Water 3- Produced water Amounts of oil in suspension & dissolved solids Water quality requirements for injection are: 1- Compatibility with reservoir rock & formation water 2- Least corrosive to injector / producer / facilities. 3- Environment friendly

7 A Typical Water Flood Project Crude Oil Dehydration Emulsion Stability caused by Presenceofsolids High viscosity crude Presence of surface active chemicals Highshearforces Small volumes of dispersed phase Emulsions resolved by High temperature Electrostatic fields Use of chemical demulsifier Difficult Emulsions High viscosity High solids content (inc. corrosion product) Low ph Waxy Produced Water Management Disposal Options To Sea Environmental restraints - Water quality To Producing Reservoir Compatibility - Water quality - Treating/fracturing Long term effects To Water Aquifer Compatibility - Water quality - Long term effects Effect on shallow water aquifers 27 28

8 Produced Water Management Produced water in a waterflooding project comes from two sources: 1. 'DESIRABLE' water - it flows through the reservoir while pushing or dragging oil with it. It increases continuously as the flood progresses. 2. 'UNDESIRABLE' water - it moves through the reservoir without pushing or dragging oil with it. It also increases continually with the maturity of the flood. Produced Water Management The project economics will warrant reducing cost of water production. One must make an effort to reduce if not totally eliminate the 'undesirable' water. Also, an effort must be made to reduce the 'desirable' water. Mobility Ratio Produced Water Management 1. High cost of injection. 2. High cost of production - reducing well rate due to increasing flowing bottom hole pressure, scaling, corrosion, facilities modification for oil-water separation and water disposal. 3. Environmental concerns Produced Water Management The first requirement for' water management is the identification of the nature of water produced and its possible cause's. The success of the remedial action will depend upon its correct identification and the choice of the right corrective procedure

9 Typical Water Quality Criteria Oil content Oil characteristics Dissolved chemicals Suspended solids Scaling propensity Asphaltenes Treatment of Water for Waterflooding Bacteria Check the compatibility with the formation rock Quantity ph of Natural Waters Waterflood Performance Measurements Alkaline soil run off 10 Seawater 8-9 River water 7 Rain water 6 Peat and organic waters 4 Mine waters 3 Mineral springs 1-2 Economic success of a waterflood project depends on the additional recovery obtained. The cost of the water, injection wells, and surface treatment facilities must be less than the value of the additional oil recovered

10 Waterflood Performance Measurements Water Flood Planning in an Economic Perspective Before an economic evaluation can be made, the reservoir engineer must predict the following waterflood performance indicators. Oil Production Rate (STB/day) Water Injection Rate (STB/day) Water-Oil Production Ratio (STB/STB) Optimum Timing for a Water Flood As a rule of thumb, a water flood project is initiated at a time prior to reservoir declining to a level of psi higher that the saturation pressure. Key Questions in Designing a Water Flood 1- What does the reservoir look like? External configuration. Internal continuity of pore space and layers. 2- Natural water drive? Aquifer type, shape, size and continuity. Aquifer strength

11 Key Questions in Designing a Water Flood 3- Is the reservoir floodable with water? Current oil saturation & distribution. Oil and water viscosity and mobility ratio. Optimum timing for flood. Need of a pilot when & where. Development plan - Well pattern peripheral or in-field. - Well locations - Well completion philosophy. Key Questions in Designing a Water Flood 4- How much incremental oil? Oil, water and gas production rates profile. Profitability 5- Other pertinent matters? Facilities modification & additional facilities. Performance concerns. Risk mitigation plans. Water handling and disposal Key Questions in Designing a Water Flood Sweep monitoring program. Flood optimization plan. Enhance oil recovery (EOR) scheme. Current pressure. Production oil only or oil+water+gas. Water source. Water Injection to Sweep Oil Five - spot Injector/producer patterns sweep oil from injectors to producers more effectively as they increase reservoir pressure. Production well Injection well Future inj. well 43 44

12 Pattern Configurations Peripheral or Repeating Pattern Flood Waterflooding patterns are characterized by the configuration of the injection and production wells. Several basic flood patterns will be presented in this section. Two basic types: peripheral and repeating pattern flooding. The reservoir engineer must decide which to implement. The reservoir boundaries & physical rock characteristics help to determine which flooding approach is most appropriate Peripheral or Repeating Pattern Flood A narrow, long reservoir may perform better if waterflooded from end to end. This is especially true for a dipping reservoir where gravity segregation can be used to assist in the displacement. A large surface area reservoir is often more suited to a regular spaced repeating geometric pattern of injection and production wells. Peripheral Flood Consists of injecting water into wells along the edge of the reservoir Generally yields maximum oil recovery with minimum of produced water Due to small number of injection wells in peripheral flood, recovery response will occur after a long time delay

13 Peripheral Flood If peripheral waterflood is implemented, when flood front from injection wells breaks through at production wells, these wells are often converted to injection wells. Oil will continue to be produced from wells ahead of front and overall water rates are kept as low as possible. A reservoir that pinches out along edges with low permeability and thus low productivity would not be a good edge drive reservoir since the injectors would have low injectivity resulting in poor waterflood performance. Waterflood Patterns Peripheral (At the edge or periphery of the reservoir) Advantages: Better areal sweep, increase displacement efficiency, for partial water drive reservoir. Disadvantage: The response to the water injection is limited to the producers, not respond quickly Uses: in smaller reservoirs or combination with pattern Waterflood Patterns Pattern (irregular and regular repeating patterns) Injector/Producer Ratio Direct & Staggered Line Drive: Ratio is 1/1 4-spot, 5-spot, 7-spot and 9-spot patterns: injector/producer ratio and concept Repeating Pattern Flood Repeating pattern floods use injection-production well pattern to cover all or part of reservoir. This pattern is an element of symmetry and has, theoretically, no flow boundaries. The pattern can be studied to determine its performance during waterflooding and this information is used to predict field wide waterflood performance

14 Repeating Pattern Flood Number of injectors in field developed suing repeating patterns is greater than for peripheral development plan. As a result, the response time is shorter due to increased injection capacity. Increase injection capacity also results in increased production capacity. Basic Flood Patterns Repeatable flood patterns Linedrive 4-spot 5-spot 7-spot 9-spot Basic Flood Pattern Guidelines Patterns are often referred to as regular or inverted Regular patterns have only one production well per pattern Inverted patterns have only one injection well per pattern Peripheral Flooding Injectors Producers 55 56

15 Optimum water flood pattern Peripheral flood All injection wells are located at or below the oil water contact, while all producers are located structurally higher locations. Optimum Water Flood Pattern Pattern floods Wells are drilled to form a repeating pattern. Many patterns have been used, but the 5-spot and 9-spot patterns are the most popular Line Drive Patterns 5-Spot Pattern Direct Drive Staggered Drive Injection Well Production Well No-flow Boundary Injection well Production well No-flow boundary 1 : 1 injector-to-producer ratio Most common pattern Uniform well spacing High sweep efficiency Regular & inverted 5-spot are identical Special case of a staggered line drive with square drilling pattern 59 60

16 Spot Pattern Normal Inverted Injection Well Production Well No-flow Boundary Not commonly used due to irregular spacing If used, inverted pattern preferred - has more production than injection wells May be used for pilot floods in normal pattern form because it results in good control of flow during a test flood 63 9-Spot Pattern Normal Nine - Spot Inverted Nine - Spot Injection Well Production Well No-flow Boundary Second most common pattern used in waterflooding In inverted patterns, the difference in distance of the corner wells and the side wells from the injector causes difficulties with breakthrough as corner wells see less fluid from the injector. Inverted pattern preferred - more production than injection wells Uniform well spacing developed from square drilling pattern Good sweep 64

17 5-Spot 4-S pot 9-Spot Factors in Pattern Selection Direct Line Drive 7-S pot Current well locations Fracture azimuths Permeability anisotropy Field geometry Injectivity Infill drilling plans Casing integrity of conversion injection candidates Adjacent lease considerations Factors Affecting Pattern Selection Following criteria, presented by Craig, are commonly used. Provide desired oil production rate Provide sufficient water injection capacity to yield desired oil production rate Maximize oil recovery with minimum water production Factors Affecting Pattern Selection Following criteria, presented by Craig, are commonly used. Take advantage of reservoir non-uniformities such as fractures, permeability trends, dip, etc. Be compatible with existing well pattern and require a minimum of new wells Be compatible with flooding operations on adjacent leases 67 68

18 Factors Affecting Pattern Selection Comparison of the economics of possible flooding schemes is used to determine final selection of spacing, pattern type and orientation of the pattern. Waterflooding is a secondary recovery process. Pattern selection is often controlled by well locations that result from primary field development. The cost of drilling new wells frequently dictates that existing wells be used and that few if any additional wells be drilled. Factors Affecting Pattern Selection In order to prevent early breakthrough due to water channeling from injection to production wells, the line connecting adjacent injectors should be made parallel to the direction of maximum permeability or fracture trend Factors Affecting Pattern Selection Physical Restrictions: Geographical Directional Permeability Directional Fractures Existing Wells Reservoir Geometry Factors Affecting Pattern Selection Legal Considerations: Minimum Spacing Adjacent Leases 71 72

19 Factors Affecting Pattern Selection Process Considerations: Injection Rate Response Time Production Rate Mobility Ratio Flood Life Factors Affecting Pattern Selection Economic Considerations: Cost Revenue Rate of Return Design Aspects 1. Design Process 2. (Quality- Compatibility-Recycling of Produced Water) 3. Water Injection Rate Volume Requirements 4. Optimum Timing 5. Optimum Pressure Level 6. Fluid Saturation at Start of WF 7. Residual Oil Saturation at End of WF Design Aspects 8. Optimum Well Pattern 9. Injection Philosophy 10.Injection Well Requirement 11.A Pilot Project 12.Surface Facilities 13.Generalized Response to a Typical WF 75 76

20 Conceptual Planning Conceptual Planning Data gathering Location of the field (offshore, onshore) Field terrain and accessibility Shape of the reservoir Volumes of in place hydrocarbons i- Initially and at present. ii- Oil, gas and water saturations and their distributions Reservoir characterization i- Rock and fluid properties ii- Vertical and areal variations iii- Zonal continuity, fractures and faults iv- Formation dip v- directional permeability vi- Gas cap & aquifer: size and connectivity Conceptual Planning Previous reservoir development i- Number and type of wells. ii- Well productivity and completions iii- Location of wells iv- Gathering and separation facilities v- Production practices natural flow or lift. vi- Production history oil, gas and water. vii- Problems reservoir, environment and well related. viii- Studies development and economics related 2- Preliminary Designs These designs will provide most of the following information: 1- Phase or full development 2- Project life 3- Initial oil rate (decline rate considerations) 4- Production rate forecasts 5- Water injection rate 6- Waterflood lay-out and well spacing 7- Sources of injection water 79 80

21 2- Preliminary Designs 8- Disposal of produced water 9- Preliminary facilities design 10- CAPEX and OPEX estimates 11- Economic analysis 13- Risk and mitigation plans 14- Reservoir / well monitoring programs 15- Logistics and infra structure 16- Additional data requirement 81