10 1 Production Forecast EM

Reservoir Simulation - Production Forecast

Data review

• Why run a flow simulation ? • Mathematical & Numerical considerations • ECLIPSE Reminder

Introduction

Etienne MOREAU







History matching

Space & Time Discretisation Reservoir description Fluid description Initial State Aquifer & Well representation Flow description




Production Forecast

• • • • • •




Outline

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EP - Reservoir Simulation - Production Forecast - E.M.










Good Production forecasts will depend on

Introduction • Good history match • Good integration of well performance and production constraints

Well performance • Inflow curves − Productivity index or complete curve • Outflow curves − VFP tables

Production constraints • Constraints related to flow − Maximum water-cut or maximum GOR per well − Maximum water production or gas production for a group of wells • Constraints related to pressure − Minimum bottom hole flowing pressure − Minimum well head pressure

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Gas Gas metering P sep. P = separation pressure Oil metering

Oil

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EP - Reservoir Simulation - Production Forecast - E.M.

PWF Well inflow

PR

Down hole choke

Fluid produced

Safety valve

Surface choke

Pt

Wells representation : Outflow Performance (1)

EP - Reservoir Simulation - Production Forecast - E.M.

Surface facilities Vertical lift

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800

1200

1600

Increasing GOR

Increasing Tubing Size 5

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400

800

1200

1600

IPR: Inflow Performance Relationship VLP: Vertical Lift Performance

Well capacity 940 m3/d

Wells representation : Well control (fixed THP)

Increasing Well Head Pressure

Wells representation : Outflow Performance (2)

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Liquid flow (m3/d)

Increasing Water cut

250

200

150

150

50

0

250

200

150

100

50

0

Liquid flow (m3/d)

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EP - Reservoir Simulation - Production Forecast - E.M.

Bottom Hole Flowing Pressure (bar) Bottom Hole Flowing Pressure (bar)










Main controls

Well Controls: Principal uses in forecast mode • Imposed Flow rate − Oil, Water, Gas, Liquid, Reservoir voidage • Imposed pressure − Tubing Head Flowing pressure − Bottom hole flowing pressure

Secondary controls • Flow rates − Economic limits − Rates upper limit per phase − Maximum ratios (Wcut, GOR, WGR) • Pressures − BHP and THP limit (lower for a producer, upper for an injector) − Maximum drawdown

VFP tables are used to relate bottom hole to well head pressures

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Well Controls: Eclipse keywords WCONPROD : Control data for production wells WECON : Economic limit data for production wells WEFAC : Well efficiency factors (for downtime) WELLDRAW : Maximum drawdown per producer WCONINJE : Control data for injection wells WECONINJ : Economic limit data for injection wells

Dimensions in RUNSPEC

• VFPPROD : VFP tables production wells • VFPINJ : VFP tables for injection wells

VLP table

• • • • • •

Well controls

EP - Reservoir Simulation - Production Forecast - E.M.










• VFPPDIMS : Production wells VFP table dimensions • VFPIDIMS : Injection wells VFP table dimensions

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EP - Reservoir Simulation - Production Forecast - E.M.







Inflow

Inflow & Outflow calculations • Pressure drop between cell and bottom hole (section 1)

Outflow

L

2 1

3

I+1, j

Head

3

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Inflow & Outflow calculations

Horizontal well

2

• Pressure head between connection and datum of VFP table (section 2) • Head losses in tubing (section 3)

I, j

Tubing

I -1, j

Deviated well

Reminder

• BHP = f (Q, THP, Wcut, GOR, Qlift)

• use of Vertical Flow Performance (VFP) tables provided in the data set

Pressure drop in tubing (section 3)

• horizontal well : hydrostatic head + friction if WFRIC or MSW

• Vertical well: hydrostatic head ρ g ∆z between the connection i and the well’s datum + (correction up to VFP datum depth)

Wellbore pressure head (section 2)

kr Q = CF× × (Pr − Pf) µ

Inflow performance relationship (section 1)

EP - Reservoir Simulation - Production Forecast - E.M.













• it is important to define accurately the VFP tables when the inflow drawdown is low

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EP - Reservoir Simulation - Production Forecast - E.M.

VFP tables are generally generated by well department

Outflow calculations: VFP tables generation


It is recommended

The parameters must cover the range of values which will be reached during the forecast simulations: NO EXTRAPOLATIONS !

• To group wells according to their deviation, completion and produced fluid

• To generate one table for each value of tubing diameter

• To use the PVT corresponding to produced fluids










Some BHP may correspond to a combination of parameters physically impossible. • Values higher than the max reservoir pressure should be given to ensure that the well flowing conditions will not enter the forbidden region

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Matching of well performance

At the beginning of production forecasts

• It is pointless to try to match BHP and THP as long as reservoir pressure is not matched • It is highly recommended to match BHP and THP as soon as reservoir pressure is matched by introducing the VFP tables and adjusting PI.

During history match

• not used during history match (Wells are controlled in flow rate) • used during production forecasts (Well flow rates are directly linked to well performance)

Well performance parameters are :

EP - Reservoir Simulation - Production Forecast - E.M.










• BHP and THP must be matched per well to ensure the continuity from boundary conditions in flow (HM) to BC in pressure (forecast)

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EP - Reservoir Simulation - Production Forecast - E.M.







Matching of well performance : BHP per well BHP per well can be modified by • Tuning of Connection factors • Introduction of production uptimes − use observed daily Q + WEFAC instead of monthly averaged Q

• use of WPIMULT or modification of the skin

Reminder : Tuning CF per layer may be necessary for PLT match • the information provided by the PLT (allocation of flow per layer) must be taken into account since the match in P (K per layer) • It is recommended to adjust the skin per (group of) layers • Use instantaneous rates (not monthly averaged) and be sure that everything (P, measure conditions) is consistent

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This intersection may be in the unstable part of the VFP curve; in this case the results are very sensitive to the slope of IPR

• Linear portion of VFP table at flowing conditions (GOR and WCUT) • Local IPR: BHP = Pr - (Q /IP)

Eclipse solves for the intersection of:

• Modification of pressure head between connection and datum of VFP table • Modification of VFP table

BHP per well can be modified by

Matching of well performance : THP per well

EP - Reservoir Simulation - Production Forecast - E.M.













it is recommended to discretize each parameter in VFP curves with enough values to represent correctly the working point

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EP - Reservoir Simulation - Production Forecast - E.M.