How Do Solid Expandable Tubulars Enhance Deep Well Value?

At-a-Glance: Solid expandable tubulars (SETs) preserve hole size, unlock total depth (TD) in tight pressure windows, and eliminate sidetracks by providing contingency liners, openhole clads, and casing patches with minimal inner diameter (ID) loss—cutting days, cost, and risk in deep wells.

Deep-well value drivers: fewer casing strings, larger final completion ID, reduced non-productive time (NPT), improved well integrity, and lower emissions via fewer rig days.

I. Objective & KPIs

• I.1 Objective: Maximize deep-well deliverability and reliability by using SETs to manage narrow pore-pressure/fracture-gradient (PP–FG) windows, maintain larger IDs to TD, and provide contingency isolation without sacrificing completion size.
• I.2 Primary KPIs:
  • TD attainment without sidetrack (% wells) and average casing strings used (count/well)
  • Final completion drift ID (in) and retained bore fraction (%)
  • NPT related to losses/stability (hours/well) and contingency events resolved (count)
  • Rig time saved vs. base plan (days/well) and well construction cost ($/ft)
  • Integrity KPIs: leak-off test (LOT)/formation integrity test (FIT) margins, pressure test pass rate (%)
  • APB management: annulus pressure margins (psi)
  • GHG proxy: rig-day reduction (tCO2e/well)

II. Critical Parameters & Target Ranges

Assumptions (estimated): HP/HT deep well, PP–FG narrow window, requirement to run a large-bore production string. Values below reflect typical industry ranges; finalize via project-specific engineering.

Key formulas

• Expansion ratio: E = \dfrac{D_f}{D_i}
• ID retention (%): \text{Retention} = 100 \times \dfrac{\text{Drift ID}_{\text{after}}}{\text{Drift ID}_{\text{before}}}
• Equivalent circulating density (ECD): \text{ECD} = \rho_m + \dfrac{\Delta p_{\text{ann}}}{0.052 \times TVD}
• Hydraulic power for expansion: P_{\text{hyd}} = \dfrac{Q \times \Delta p}{1714} (HHP; Q in gpm, ?p in psi)
• APB estimate (simplified): \Delta p_{\text{APB}} \approx \beta \, \Delta T \, \dfrac{V_f}{V_c} (ß: effective thermal compressibility; validate via detailed model)
• Turbulent friction scaling (production impact): \Delta p_f \propto \dfrac{L \, q^2}{D^5} (larger ID strongly reduces friction loss)

III. Step-by-Step Procedure / Workflow

1. III.1 Pre-job engineering
   • 3D geomechanics: refine PP–FG and depletion/thermal loads to set landing depths and contingency points.
   • Well architecture: plan hybrid stack (conventional + SET) to preserve final completion ID; include at least one contingency SET string.
   • Load cases: burst/collapse/tension, thermal and APB; apply post-expansion derating and safety factors.
   • Hydraulics: confirm rig pump capacity for required Q and ?p at depth; verify surface iron and BOP bore clearance.
   • Completion interface: validate pass-through OD for liner hangers, packers, perforating, and artificial lift strings.
2. III.2 QA/QC and system readiness
   • Full-length drift, thread inspection, and hardness checks on all expandable joints; ensure cleanliness and dope compatibility for expansion.
   • Surface integration test: function-test expansion tool, pressure-compensated seals, and datalogger; calibrate cone friction.
   • Contingency kit staged: spare cones, seals, pull/overpull subs, fishing necks, and cleanout BHA.
3. III.3 Running the expandable string
   • Circulate hole clean; condition mud to target rheology and density to minimize ECD during expansion.
   • Run at controlled speed; monitor drag and standpipe pressure for early indication of tight spots.
   • Position shoe/top of liner per plan with overlap as required for tieback or clad operations.
4. III.4 Cement program (as applicable)
   • Stage cement if necessary to stay within FG; use low-ECD placement (spacers, foamed or ultralight blends if permitted).
   • Account for post-expansion sheath integrity; utilize flexible systems where thermal/pressure cycling expected.
5. III.5 Expansion execution
   • Initiate expansion with pressure ramping to the calibrated ?p; maintain rate within planned ft/min to control heat and uniformity.
   • Real-time monitoring: cone position (strokes), ?p across cone, Q, temperature; halt on abnormal trends (stall or sudden ?p drop).
   • Set anchors/hangers as designed; confirm via weight/pressure signatures.
6. III.6 Post-expansion verification
   • Pressure test to planned limit; run drift and multi-finger caliper (MFC) or ultrasonic imaging for ID and ovality.
   • CBL/VDL/USIT (if cemented) to verify isolation; remediate with sealant squeeze if required.
   • Update as-built loads and finalize completion pass-through plan.
7. III.7 Use-case workflows
   • Contingency liner to TD: Install SET to isolate losses/instability, keeping larger ID to run target production string.
   • Openhole clad (loss cure): Expand across thief zones without cement first; seal with elastomer/metal-to-formation contact; follow with cement if needed.
   • Casing patch/repair: Mill localized damage; run SET patch; expand and pressure test to restore integrity with minimal ID loss.

IV. Risk & Mitigation (HSE, Reliability, Integrity)

• IV.1 Collapse/burst margins reduced after expansion
  • Mitigation: derate in design; validate with full load-case matrix including APB; consider thermal relief subs or annulus management.
• IV.2 Cone stall or tool failure
  • Mitigation: clean hole, control doglegs, stage pump rates, maintain contingency cone/seal kits; define maximum allowable stall attempts and pull procedure.
• IV.3 Excess ECD and induced losses during expansion
  • Mitigation: MPD or constant bottomhole pressure methods; rheology tuning; rate ramping; track ECD vs. FG in real time.
• IV.4 Sour service cracking/corrosion
  • Mitigation: select sour-rated metallurgies; post-expansion stress relief via controlled schedules; compatible inhibitors.
• IV.5 Cement sheath debonding/microannulus
  • Mitigation: flexible cement systems; scratchers/centralization plan; expand-then-cement or cement-then-expand per zone requirements.
• IV.6 Thermal and APB loads in deep sections
  • Mitigation: engineered trapped-annulus volumes, relief valves, or flow paths; temperature cycling simulations and monitoring.
• IV.7 HSE
  • High-pressure pumping and hot surfaces; implement red zones, pressure testing barriers, and lockout/tagout on surface iron.

V. Optimization Levers (Performance & Cost)

• V.1 Architecture optimization
  • Design for one fewer conventional casing string by inserting a planned SET contingency; preserves final production ID and reduces casing/times.
• V.2 Real-time analytics
  • Stream ?p, Q, strokes, temperature; apply limits-logic to detect ovality or non-uniform expansion early; auto-ramp rates to hold ECD target.
• V.3 Fluid engineering
  • Low-gel, flat-rheology systems to minimize surge/swab and ECD; lost-circulation material (LCM) compatibility verified for expansion clearances.
• V.4 MPD synergy
  • Use MPD to keep bottomhole pressure within PP–FG during expansion and cement placement; tighten operating window and prevent losses.
• V.5 Surface system readiness
  • Ensure pump HHP, clean tanks, and high-resolution flow-out measurement; reduce flat time between runs and expansion initiation.
• V.6 Reliability-centered maintenance
  • Pre-job NDE on cones and mandrels; replace wear components proactively based on cycle counts; maintain spare kits at rig site.
• V.7 Economics focus
  • Track days saved and ID preserved to quantify value: larger ID reduces completion friction losses and equipment constraints, boosting drawdown capacity.

VI. Verification & Monitoring Plan

• VI.1 Before operation
  • Acceptance criteria: full drift, pressure test of tool string, baseline hydraulics and ECD model validated against last circulation data.
• VI.2 During expansion
  • Record: ?p across cone, Q, strokes (position), temp, standpipe pressure, ECD at depth; trigger alarms at ±10% deviation from plan.
  • Witness: weight set/anchor events; log time–depth–pressure for each joint.
• VI.3 After expansion
  • Pressure test (hold per spec), mechanical drift, MFC/ultrasonic log; cement bond evaluation where applicable.
  • Integrity sign-off: confirm burst/collapse margins vs. updated loads; verify completion pass-through with a gauge ring.
  • KPI capture: rig time used, NPT avoided, ID retained, number of remedial events avoided, emissions reduction from saved days.

How SETs Enhance Deep-Well Value—Operational Summary

• Reach TD without sacrificing completion size: Maintain larger IDs across contingency strings, preserving production capacity and intervention access.
• Control PP–FG risk in deep sections: Isolate losses/unstable intervals with minimal added restriction, enabling continued drilling and safe cementing.
• Reduce sidetracks and NPT: Rapidly deploy openhole clads or patches to cure losses and casing damage, converting high-risk time to progress time.
• Lower well construction cost and emissions: Fewer casing strings and fewer rig days directly reduce OPEX and GHG footprint.
• Improve long-term integrity: Customized metallurgy and cement strategies handle HP/HT and sour environments while managing APB.