Сomparative analysis between:
- the reservoir fluid deliverability (the ability of reservoir to produce or take-in the fluid) which is called Inflow Performance Relation (IPR)
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- wellbore fluid deliverability (the ability of well to lift up or lift down the fluid) and which is called Lift Curves (LC) (also called Vertical Lift Performance (VLP) or Tubing Performance Relation (TPR) )
It is based on correlation between surface flowrate
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Definition
WFP – Well Performance Analysis is a specialized analysis of correlation between surface flowrate and wellbore pressure as function of formation pressure and associated production optimization procedures.
Application
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Technology
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WFP is performed on stabilised flow and does not cover transient behavior which is normally covered in Well Tests domain.
The flow is called stabilised if the well productivity index is not changing over time.
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On the other hand, the constant rate flow may not represent a stabilised flow as the bottom-hole pressure and productivity index maybe still in transition after the last rate change.
The WFP methods are not applicable if the well flow is not stabilised even if the flow rate is maintained constant.
There are two special reservoir flow regimes which are both stabilised and maintain constant flow rate: steady state regime (SS) and pseudo-steady state regime (PSS).
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The pseudo-steady state (PSS) regime is reached when the flow is stabilised with no pressure support at the external boundary.
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As for formation and bottom-hole pressure in PSS they will be synchronously varying while in SS they will be staying constant.
The table below is summarizing the major differences between SS and PSS regimes.
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constant
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constant
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constant
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constant
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Drawdown
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constant
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constant
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constant
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varying
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pressure
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constant
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varying
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Application
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- Setting up the required production or injection regime for each well upon the current formation pressure, reservoir saturation and production target specified by FDP
- Generating Lift Curves (LC) tables as input for Reservoir Flow Modelling (RFM)
Technology
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Most reservoir engineers exploit material balance thinking which is based on long-term well-by-well surface flowrate targets (whether producers or injectors).
In practice, the flowrate targets are closely related to bottomhole pressure and associated limitations and require a specialised analysis to set up the optimal lifting (completion, pump, chocke) parameters.
This is primary domain of WFP analysis.
WFP is performed on stabilised wellbore and reservoir flow and does not cover transient behaviour which is one of the primary subjects of Well Testing domain.
It's again important to avoid confusion between the termines stationary conditions (which mean that refered properties are not chaning in time) and stabilised flow conditions which may admit pressure and rate vraition.
In practice, the productivity index is usually not known at all times as there is not routine procedure to assess it.
It is usually accepted that a given formation takes the same time to stabilise the flow after any change in well flow conditions and the stabilisation time is assessed based on the well tests analysis.
Although, this is not strictly true and the flow stabilisation time depends on well-formation contact and reservoir property variation around a given well.
This is also compromised in multi-layer formations with cross-layer communication.
The conventional WFP – Well Performance Analysis is perfomed as the cross-lot with two physical models:
and
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IPR – Inflow Performance Relationship
IPR – Inflow Performance Relation represnts the relation between the bottom-hole pressure
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p_{wf} = p_{wf}(q) |
которая в общем случае является нелинейной.
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На практике удобно вести в рассмотрение понятие продуктивности скважины
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J_s(q_{\rm liq}) = \frac{q_{\rm liq}}{p_R-p_{wf}} |
для нефтяной добывающей скважины, где
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J_s(q_g) = \frac{q_g}{p_R-p_{wf}} |
the
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- Inflow Performance Relation (IPR) – responsible for reservoir deliverability (see below)
- Lift Curves (LC) – responsible for well deliverability (see below )
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The intersection of IPR and Lift Curves represent the Stabilised wellbore flow (see Fig. 1)
Fig. 1. A sample case of stabilised wellbore flow represented by junction point of IPR and Lift Curves. | Fig. 2. The dead well scenario. |
Given a tubing head pressure
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Fig. 3. A sample case of stabilised wellbore flow as function of formation pressure. | Fig. 4. A sample case of stabilised wellbore flow as function of production watercut |
Fig. 5. A bunch of IPRs at different formation pressures and Lift Curves at different THPs. |
Workflow
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- Check the current production rate against the production target from FDP
- If the diffference is big enough to justify the cost of production optimization (see point 8 below) then proceed to the step 3 below
- Assess formation pressure based on well tests
- Simulate IPR / LC based on the current WOR/GOR
- Calculate the stabilized flow bottom-hole pressure
- Gather the current bottom-hole pressure
LaTeX Math Inline body p_{wf} - Check up the calculation aganst the actual
LaTeX Math Inline body p_{wf} - Recommend the production optimisation activities to adjust bottom-hole pressure
:LaTeX Math Inline body p_{wf} - adjusting the choke at surface
- adjusting the pump settings from surface
- changing the pump depth
- changing the tubing size
- changing the pump
- adjusting the choke at surface
The above workflow is very simplistic and assumes single-layer formation with no cross-flow complications.
In practise, the WFP analysis is often very tentative and production technologists spend some time experimenting with well regimes on well-by-well basis.
See Also
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Petroleum Industry / Upstream / Production / Subsurface Production / Well & Reservoir Management
Subsurface E&P Disciplines / Production Technology
[ Inflow Performance Relation (IPR) ] [ Lift Curves (LC) ]
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References
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Joe Dunn Clegg, Petroleum Engineering Handbook, Vol. IV – Production Operations Engineering, SPE, 2007
Michael Golan, Curtis H. Whitson, Well Performance, Tapir Edition, 1996
William Lyons, Working Guide to Petroleum and Natural Gas production Engineering, Elsevier Inc., First Edition, 2010
Shlumberge, Well Performance Manual
для газовой добывающей скважины
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J_s(q_g) = \frac{q_g}{p_{wf}-p_R} |
для газовой нагнетательной скважины
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J_s(q_w) = \frac{q_w}{p_R-p_{wf}} |
для водяной нагнетательной скважины
где
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Опираясь на эти определения ИКС может быть записана в универсальном вид для всех типов скважин:
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p_{wf} = p_R - \frac{q}{J_s(q)} |
При этом в кажом конкретном случае выбирается правильный знак второго слагаемого и правильный смысл дебита
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ИКС активно используется для анализа оптимального режима работы скважины.
Для однопластовой залежи со слабосжимаемым флюидом продуктивность не зависит от дебита
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Это характерно для водозаборных скважин, водонагнетательных скважин и нефтяных скважин выше давления насыщения.
Для газовых скважин, газоконденсатных скважин, скважин с легкой нефтью, а также нефтяных скважин, где давление опустилось ниже давления насыщения
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Fig.2. IPR for compressible fluid production (gas, light oil, saturated oil)
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VLP – Vertical Lift Performance
КВЛ активно используется для анализа оптимального режима работы скважины.
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Sample Case 1 – Oil Producer Analysis
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Sample Case 2 – Water Injector Analysis
Sample Case 3 – Gas Producer Analysis
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