MECO Core-Breakout Products

Completion-Fluid Filter-Cake and Core Remediation

Product and System Specification - Openhole and Standalone-Screen Completions

MECO-CA-1 · MECO-NF-1 · MECO-HT-1 · MECO-BS-1

1.1 Scope

This specification defines product specifications, system configurations, operating parameters and

acceptance criteria for the four MECO completion-fluid core-breakout product lines in openhole and standalone-screen completions. Polymer scale is outside the scope of this document.

1.2 Pre-job filter-cake solids audit

A filter-cake solids composition analysis is mandatory before every treatment. The audit quantifies the carbonate fraction and the organic fraction of the cake, and establishes whether the polymer is present in intact or degraded form. Product selection and slug sizing are derived from these three results.

1.3 Product lines

Table 1 Product lines

2.1 Openhole versus standalone screen

The two completion modes differ in fluid contact surface and in the volume basis used to size the breakout fluid.

Table 2 Completion-mode comparison

2.2 Volumetric basis and residence time

For an 8-1/2 in. openhole completed with a 5-1/2 in. standalone screen over a 100 m interval, openhole volume is 36.6 L/m while the screen-to-wall annulus holds only 21.3 L/m. The screen path therefore carries 42 % less fluid for the same filter-cake load. Screen treatments must either raise treatment intensity per unit volume or be sized from filter-cake area; the openhole "full volume × multiple" basis cannot be transferred.

Minimum effective residence time is 6 h for all four lines. Design residence time is 8–12 h. The upper bound applies to standalone-screen completions, which require additional time for water-wetting and solids dispersion.

2.3 Screen-slot compatibility and residual solids

Slot width is matched to formation sand at slot ≈ d10–d50. Source measurements: sand median 276 μm, screen precision 275–400 μm, giving slot/d50 = 0.996–1.449. Residual solids after breakout must be finer than one third of the slot width.

Specification limit: at a 275 μm slot, dispersed D90 must be below 92 μm. Passability is verified 3–4 gauge numbers above nominal - a nominal 8.5 gauge screen is tested against an 11.5–12.5 gauge tester. Viscosity and solids reduction must be complete before the washpipe is pulled; flushing the screen on flowback is not an acceptable substitute.

3.1 Composition and injection sequence

MECO-CA-1 combines HCl, HEDP and EDTA in a single chelant-acid package. HCl and EDTA must be injected in stages at a 9:1 ratio; HCl concentration is 2.65 mol/L. Treatment volume is 3× openhole volume, equivalent to 10.98 m³ per 100 m of 8-1/2 in. openhole.

The interval must remain loss-free throughout placement, and the breakout fluid itself must not introduce new solids. Total acid-insoluble solids are held below 1.5 % vol.

3.2 Iron control

Iron precipitation is governed by Fe(OH)3 with Ksp = 2.6 × 10−39. Onset pH is set by Fe3+ concentration; computed values reproduce all three source points to within 0.01 pH.

Table 3 Fe3+ concentration versus precipitation onset pH

Specification limit: residual-acid pH must remain below the tabulated onset value. Tolerating 8000 mg/L Fe3+ requires pH < 1.42; tolerating 1000 mg/L requires pH < 1.72.

Complexation priority follows the stability-constant ratio: Fe3+/Ca2+ = 10^14.4 ≈ 2.5 × 10^14; Fe3+/Ba2+ = 10^17.3 ≈ 2.0 × 10^17; Fe3+ over Ba-DTPA = 2.0 × 10^16. EDTA therefore captures iron preferentially when iron, calcium and barium coexist, which confirms the ratio design.

Because component B is limited to 73.1 g/L, iron control is governed by slug total rather than by concentration: the total volume of component B injected in one job fixes the iron quantity that can be complexated. Volume calculations are carried out in slug units and are not converted from concentration.

3.3 Temperature window and ligand selection

The application range is ambient to 120 °C. Above 120 °C the thermal stability of EDTA becomes marginal and DTPA-type ligands are required; the Ba chelation log K of DTPA is 8.8, one order of magnitude above the 7.8 of EDTA. The EDTA version must not be quoted for wells above 120 °C.

Contact us