Planning and Execution of a Field Trial Utilising New Invert Emulsion Squeeze Technology

Abstract

A chemically advanced, safe, controlled delivery system, utilising invert emulsion technology, with the aqueous phase containing scale inhibitor in solution, has been developed and manufactured for evaluation in a North Sea field trial. Benefits arising from the implementation of this new technology include rapid oil returns in an immediate post-squeeze era, reduction of deferred or lost oil costs, the potential to improve contact between inhibitor and in-situ adsorption sites and the ability to formulate packages for sensitive formations and low water cut wells. It is important for squeeze operations, that the emulsion can be injected safely downhole and encouraged to "break" during shut-in, allowing the aqueous inhibitor to be released and contact the pore structure, promoting effective retention. The "broken" oil phase maintains continuity between pore spaces and promotes rapid oil productivity to return, post-squeeze, as a result of relative permeability effects. The product will provide a safe application route for scale control in wells with pressure support limitations, drawdown restrictions and water sensitive formations. This paper reviews the team approach undertaken by chemical process plant, service company, oil company consortia and research and technology service providers to facilitate the first field trial of this novel, scale squeeze process. Extensive experimental evaluations and plant scale-up trials have been undertaken to develop a suitable chemical for field use. Emulsion manufacture requirements, phase volume considerations, destabilisation routes and rheological characteristics are discussed. Laboratory and offshore compatibility trials with appropriate field fluids are reported, together with core-flood investigations, these experiments reveal equivalent inhibitor returns to normal squeeze treatments, but post-squeeze oil production for the emulsion system shows inherent benefits. A well with a sulphate scaling problem and history of deferred oil production post-squeeze has been selected for a field trial of this new technology. The field treatment is discussed and preliminary post-squeeze results evaluated. Introduction & Concept Conventional squeeze injection strategies employ inhibitor based formulations and brine overflushes to penetrate radial distances of ~12 feet, yet relative permeability effects dictate that following shut-in, water production will be favoured, whilst oil will have to overcome physical barriers, before oil continuity between the pore spaces to the well bore can be achieved. The major costs associated with inhibitor squeeze practices therefore are those incurred as a direct result of deferred oil production, arising from failure to return to pre-squeeze oil productivity for prolonged periods. Formation damage and sand production may also be encountered in sensitive formations owing to the large volumes of active chemical being injected into the near well-bore region. An alternative to conventional squeeze treatments is presented and involves the use of invert emulsion technology, with the aqueous phase containing the scale inhibitor in solution. The use of invert emulsion technology in the oil industry is not new and has been successfully used in applications ranging from muds to retarded acids1,2. Controlled destabilisation downhole is necessary to facilitate in-situ "breakage" and release of separate oleic and brine phases. The oleic phase ensures oil continuity between pore spaces and provides desirable relative permeability characteristics, whilst the segregated brine phase now enables effective deposition of chemical inhibitor to the rock structure.

Mechanistic Understanding of Rock/Phosphonate Interactions and the Effect of Metal Ions on Inhibitor Retention

“…23,24 Using the solution speciation model for DTPMP, 25 and assuming a stoichiometry of Ca 3 H 4 DTPMP, the solubility products, estimated from phase II and phase III of DTPMP return concentrations, are 10 -52.3 and 10 -53. 8 . Similarly, the solubility product, estimated from phase III BHPMP return concentrations, is 10 -39.9 by assuming a stoichiometry of Ca 4 H 2 BHPMP and the published speciation model.…”

“…1,2 More recent papers have advanced the knowledge of inhibitor reactions under various production conditions. [3][4][5][6][7][8][9][10][11][12] The primary conclusions from several previous studies of NTMP(aminotri(methylene phosphonic acid))calcite reaction are [13][14][15][16] : (1) The extent of NTMP retention by carbonate-rich formation rock is limited by the amount of calcite that can dissolve prior to inhibitor-induced surface poisoning; (2) Calcite-surface poisoning effect is observed after approximately 20 molecular layers of phosphonate surface coverage that retards further calcite dissolution; (3) The consequence of retarded calcite dissolution is that less basic ion, − 2 3 CO , is released into solution, leaving the solution more acidic; therefore, more soluble calcium phosphonate solid phases form.…”

Field Experiences Using ‘Oil Soluble’ Non-Aqueous Scale Inhibitor Delivery Systems

“…The work by Kaufman and Dexter was followed by that of Bourne, Lawless, Smith, Collins and others [7][8][9][10][11][12][13]. These workers attempted to extend the technology of emulsion delivery systems to ensure, as far as practicable, that the emulsion breaks down after injection into the producing formation.…”

Field Application of Emulsified Scale Inhibitor Treatment to Mitigate Calcium Carbonate Scale in Horizontal Wells

“…The third method includes injection of the inhibitor in a micro-emulsion form. [16][17][18] Still a fourth method that was developed by Nasr-El-Din et al 19,22 included preparing the scale inhibitor in a macroemulsion form. The emulsion consists of 30 vol% diesel and 70 vol% aqueous phase, which contained the scale inhibitor.…”