Inverted ESP Sizing — Downhole Water Sink

Sizes an electric submersible pump that runs inverted in a downhole water sink (DWS) or downhole water loop (DWL) completion: water drained below the oil–water contact is pumped down through an isolation packer and re-injected into the base of the same aquifer. Nothing is lifted to surface, so the system curve is drainage drawdown plus injection build-up plus a short friction path — for a hydrostatically connected aquifer, a straight line through the origin.


Design by rate, or by sink: enter the drawdown wanted at the drainage perforations and the design rate becomes PI × sink. From the loop hydraulics (or a known TDH) and a vendor single-stage curve it returns the design TDH, split in feet into sink head, injection head, static head and friction; the stage count, brake horsepower, BEP and operating-point efficiency; the sink at the operating point; the drive frequency that delivers each rate; motor loading, motor cooling velocity, packer differential and shaft thrust. With injectivity close to the PI the design TDH is about twice the sink head, because the pump also has to re-inject the water it drains. Two print-ready charts: the pump performance curve against the system curve, and the variable-speed (tornado) chart.

Two input checks: an SG outside the plausible brine range (a psi/ft gradient typed into the SG cell), and a static head between the zones that is not about zero (zone pressures and spacing that do not describe one connected aquifer). An injection static pressure of 0 is computed for the same-aquifer case.

The functions the PO.ESP.* catalog lacks are defined as workbook LAMBDAs: PO.ESP.DWS.TDH, PO.ESP.Affinity.Rate, PO.ESP.Affinity.Head, PO.ESP.Affinity.Power, PO.ESP.Curve.HeadAtSpeed, PO.ESP.Curve.PowerAtSpeed, PO.ESP.Motor.CoolingVelocity, PO.ESP.Shaft.Thrust.

Inputs

Named cells you can edit — every result recalculates from them.

Name Description Default Unit
DWS_Q Target water rate (drainage = injection) 3000 bbl/d
DWS_Sink Target sink at the drainage perforations (0 = design by rate) 0 psi
DWS_SG Water specific gravity 1.07 —
DWS_Pdr Drainage zone static pressure 3200 psi
DWS_PI Drainage productivity index 10 bbl/d/psi
DWS_Pinj Injection zone static pressure (0 = same aquifer as the drain) 3246 psi
DWS_II Injectivity index 8 bbl/d/psi
DWS_dZ Vertical distance, drainage to injection perforations 100 ft
DWS_FlowID Flow-path ID, pump discharge to injection perforations 3.958 in
DWS_FlowL Flow-path length 150 ft
DWS_TDHKnown Known TDH at the design rate (0 = use loop hydraulics) 0 ft
DWS_Fbase Catalog curve frequency 60 Hz
DWS_FreqSet Design frequency (0 = frequency that delivers the design rate) 0 Hz
DWS_StagesSet Stages installed (0 = minimum at catalog frequency) 0 stages
DWS_MotorHP Motor nameplate power at catalog frequency 60 HP
DWS_SF Motor sizing safety factor 1.10 —
DWS_MotorOD Motor OD 5.62 in
DWS_CasingID Casing (or shroud) ID at the motor 6.276 in
DWS_Temp Water temperature at the motor 180 degF
DWS_Shaft Pump shaft diameter 0.875 in
DWS_PackerRating Packer differential pressure rating 5000 psi
DWS_Qmin Pump recommended range — minimum rate 2200 bbl/d
DWS_Qmax Pump recommended range — maximum rate 3800 bbl/d
DWS_Cases Rate cases (five) 2000–4000 bbl/d
DWS_VsdF Tornado chart frequencies (seven) 40–70 Hz

The single-stage curve (DWS_CurveQ, DWS_CurveH, DWS_CurveP) on the Pump Curve sheet is example data to be replaced with the vendor's curve.

7 sheets, shown with the values the file opens with

A
1 Inverted ESP Sizing — Downhole Water Sink / Downhole Water Loop
2
3 What this workbook does
4 Sizes an electric submersible pump that runs inverted in a downhole water sink (DWS) or downhole water loop (DWL) completion. Water is drained from the water zone below the oil–water contact, boosted by the pump and re-injected into the base of the same aquifer through an isolation packer. Nothing is lifted to surface, so well depth drops out of the sizing: the pump only overcomes the drawdown at the drainage completion, the pressure build-up at the injection completion and a short friction path.
5 It returns the design TDH, stage count, brake horsepower, best efficiency point (BEP) and efficiency at the operating point, the drive frequency that delivers each target rate, motor loading and the inverted-service checks, plus two printable charts: the pump performance curve with the system curve, and the variable-speed (tornado) chart.
6
7 Loop hydraulics
8 TDH(Q) = [ (P_inj + Q / II) − (P_drain − Q / PI) ] / (0.433 × SG) − ΔZ + h_friction(Q), where P_drain and P_inj are the static pressures at the drainage and injection perforations, PI and II the drainage productivity index and the injectivity index, and ΔZ the vertical distance from the drainage perforations down to the injection perforations.
9 In one hydraulically connected aquifer P_inj − P_drain = 0.433 × SG × ΔZ, the static terms cancel and TDH ≈ Q × (1/PI + 1/II) / (0.433 × SG): a straight line through the origin. The system curve is always built as static head + (coefficient × Q) + friction(Q). If you enter a known TDH, the coefficient is calibrated so the curve passes through your TDH at the design rate.
10
11 Why the TDH is about twice the sink
12 The pump lifts water from the drainage flowing pressure (P_drain − Q/PI) to the injection flowing pressure (P_inj + Q/II), so it pays for both ends of the loop: the sink it makes at the drain, and the build-up it needs to push the same water into the injection zone. With II close to PI the two are equal.
13 Example: 2,500 bbl/d with PI = II = 22.2 bbl/d/psi and SG 1.07 in one aquifer. The sink is 2,500 / 22.2 = 113 psi, which is 243 ft of this water, and re-injecting takes another 113 psi, or 243 ft. The design TDH is therefore about 486 ft plus friction: twice the sink head. Put the other way, a pump making 243 ft in this loop creates a sink of only about 56 psi. The Design sheet splits the TDH into sink head, injection head, static head and friction, all in feet, and shows the share of the head that goes into the sink.
14
15 How to use it
16 1. Inputs — edit the blue cells on a yellow background; every other cell is calculated. Design either by rate (the target water rate) or by sink: enter the drawdown you want below static at the drainage perforations, and the design rate becomes PI × sink. Two checks sit beside the inputs: the SG against a plausible brine range (SG is not the psi/ft gradient), and the static head between the zones, which is about zero when both perforation sets are in one connected aquifer. Enter 0 for the injection zone static pressure to compute it for that case.
17 2. Pump Curve — replace the EXAMPLE curve with the vendor's single-stage curve: 12 points, ascending rate from shut-in to run-out, head and brake horsepower per stage for water (SG 1.0) at the catalog frequency on the Inputs sheet. Enter the vendor's recommended operating range for the pump.
18 3. Design — the sizing summary. Stages are set at the catalog frequency and the drive frequency is then solved so the pump delivers exactly the design rate (or enter a design frequency on the Inputs sheet). The rate-case table shows the frequency, loading and range check for each rate case.
19 4. Performance Chart and VSD Chart — both are set up to print on one page (File › Print).
20
21 Choosing the sink
22 • A stronger sink is not always better. A drainage sink much stronger than the oil completion's drawdown pulls oil down into the water drain (reverse coning) and sends it to the injection zone; one too weak lets water cone up into the oil completion. The sinks that keep both completions clean form the inflow performance window of the downhole water sink literature (Wojtanowicz and co-workers). This workbook sizes the pump for the sink or rate you choose; it does not compute that window, so check the sink with a coning analysis or a near-well model first.
23
24 Inverted-service notes
25 • Thrust: inverting the pump puts impeller weight against the hydraulic thrust. Prefer compression (fixed-impeller) stages, size the protector thrust bearing for the load on the Design sheet in both directions, and ask the vendor for the recommended operating range in inverted service.
26 • Motor cooling: with the motor on top, drainage water must flow down past it. Keep the annular velocity at 1 ft/s or more; if the motor sits in a dead leg, fit a shroud.
27 • Packer: the packer below the pump carries the pump differential pressure from below, plus start/stop surges.
28 • Injectivity: injectivity usually declines with oil carry-over and solids. Size for the end-of-life injectivity index, and stay below the injection zone fracture pressure. PI and II from separate tests ignore sink–source interference, which normally makes the computed head conservative.
29 • Gauges: the discharge sits below the intake, so a gauge-to-gauge pressure difference also includes the fluid column over the pump length.
30
31 Requirements
32 The workbook calls Petroleum Office functions (PO.ESP.*) and defines eight LAMBDA functions (Formulas › Name Manager: PO.ESP.DWS.TDH, PO.ESP.Affinity.Rate/Head/Power, PO.ESP.Curve.HeadAtSpeed/PowerAtSpeed, PO.ESP.Motor.CoolingVelocity, PO.ESP.Shaft.Thrust). It opens with the example results already calculated; recalculating after an edit needs the Petroleum Office add-in and an Excel version with LAMBDA (Microsoft 365 or Excel 2024).
Tags:
espdownhole-water-sinkdownhole-water-loopinverted-espwater-injectionpump-sizingperformance-curvevsdaffinity-laws

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