Page 44: of Offshore Engineer Magazine (Feb/Mar 2014)

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associated with mineral scaling are materials. And deposition on these spews from the bottle. Result: no change in production. At the reduced. surfaces causes problems. The surface-installed electromagnetic end of the two-week period the choke

The ClearWELL signal creates a time- technology does not alter the thermody- setting was changed to that where the

Scale chemistry varying electromagnetic feld within the namic state of the system or its evolution, maximum CaCO deposition had been 3

The materials that form mineral scales pipe, which acts as both an antenna and as with chemical treatments. Instead, it observed. The well continued to oper-

Pipelines have a fnite solubility in a fuid, and a a transmission line. As charged particles controls where and how that thermody- ate at high effciency and production system is saturated when this balance is respond, they absorb energy and move. namic evolution occurs by transmitting levels indicate no scale deposits after 10 achieved. If more materials can be dis- This movement induces nucleation, but an electromagnetic feld that interacts months of steady operation.

solved, the system is unsaturated. When it does not occur at the surface level. with the ions present in the aqueous ClearWELL was applied to control car- the solubility limit is reached, a chemical solution to generate nucleation sites. bonate scale in wells offshore Africa. In balance is created between the dissolved ClearWELL works as a threshold nucle- this instance well operation was plagued and solid forms of the substance. At the ation device. by scale build-up, which restricted and point material precipitates out of solu- The technology uses a magnetic loop eventually blocked oil production. The tion, the system is supersaturated. Many antenna to induce a radio frequency operator wanted a method to control oilfeld water systems become supersatu- signal in the metallic piping and aqueous scale as determined by bottomhole pres- rated as physical conditions change or conductive path provided by the water sure without acid treatment or installa- dissimilar waters are mixed. system. The conductive medium acts tion of capillary tubing for continuous

The thermodynamics of solubility both as an antenna and as a transmission injection of scale inhibiting chemicals. determine that in an unsaturated system, line for the current. Fig. 1 shows a graph of bottomhole overall energy is lowered when a solid There are several advantages to pressure as determined during a trial dissolves. In a saturated solution, there introducing an interaction that moves period and prior to the trial. BHP steadily is no energy advantage to being in a solid throughout the system. By delocalizing, increased prior to the ClearWELL pro- or dissolved state. In a supersaturated the system can be installed and applied gram and has remained near-constant system, overall energy is lowered when without detailed knowledge of the loca- since its introduction.

the dissolved material precipitates. tion where conditions exist for the forma- The technology can also be applied

When a material precipitates, not only tion of mineral deposits. Because the onshore. In the Ketchum Mountain is a new phase formed, a surface between current moves throughout the system, the area of West Texas, water from several the oil and new phases must be formed. device can be surface-mounted, without sources is sent to a pumping system for

It takes energy to create a surface, and intrusion into the wellbore. reinjection. Mineral content of the waters this energy is not accounted for in the produces signifcant BaSO that reduces 4

Application examples bulk description of solubility.

The energy liberated when forming a Offshore scale control is a complicated

Fig. 4 – Mineral deposits had reduced precipitate is proportional to the amount endeavor. There are logistical issues pump efectiveness and lifetime in a reinjection system. No deposits occurred of the material undergoing transition. associated with timely chemical deliv- after installation of the ClearWELL

The energy demand to make the new ery as well as environmental concerns

ONSHORE. OFFSHORE. system: (A) shows the pump condition phase is proportional to the size of new associated with any chemical residues at startup; and (B) shows it after three surface created: a deposit’s surface area. which may be released into the environ- weeks (SPE 133526).

In a supersaturated metastable state, ment. Environmental concerns have

EVERY SHORE.

the system is waiting for enough energy to Forming a new phase always requires been especially problematic in North Sea begin the phase change. When a particle energy from the environment to start applications. ClearWELL has been tested

Certi? cation | Training | Events | Standards | Statistics | Safety begins to grow, an insuffcient amount of the process. If the only energy source is by an international operator off Denmark

Washington, D.C. | Houston | Beijing | Singapore | Dubai | Rio de Janeiro energy is released by the phase change to from the native environment, energy is in the North Sea, on a platform well 877.562.5187 (Toll-free U.S. & Canada) | +1.202.682.8041 (Local & International) | [email protected] | www.api.org create the surface. The particle’s large sur- limited. The systems normally develop with a dry tree producing from a chalk face area-to-volume ratio means that the according to the principle of least action, reservoir. Treated seawater was used for energy released from its formation may i.e., whatever requires the least amount reservoir pressure support. Historical not be suffcient to form the surface sur- of energy from the environment occurs operation of the well resulted in severe rounding the particle. If the system cannot most rapidly. Thus, deposits form under calcium carbonate deposition through- acquire this energy from fuctuations in natural evolution of the system. out wellbore and surface equipment. the surroundings, the energy remains The ClearWELL system works by chan- Chemical control is impractical and the trapped. While thermodynamics says the neling energy from an external source deposit problem has been historically system must form a precipitate eventually, into the materials that will form the new managed by reducing the choke setting to the system can’t begin the process. phase, providing suffcient energy for minimize pressure drop. This severely

If the new phase develops on an exist- the new phase to form in suspension impacts the rate at which oil can be ing surface, then fewer boundary surfaces rather than on an existing surface. This produced. Even with the reduced choke must be created. Less energy is required channeling of energy to alter the natural setting, acid treatments were required to make a solid crystal at an existing evolution of a metastable system is illus- on a nine-month schedule to maintain surface than in solution, so scale forms trated with a carbonated beverage and an production. Historical data showed that ® at surfaces. Unfortunately, when the new ultrasonic cleaning bath. When ener- at full choke well scale up occurred in

It’s a tough business. Look to API.

phase forms on an existing surface, it gized, the bath generates high-intensity approximately two weeks. adheres strongly to that surface. At the sonic waves that impinge on a partially ClearWELL-R was installed in March

Copyright 2014 – American Petroleum Institute, all rights reserved. API, the API logo, the “Onshore” slogan and the “Tough” slogan are either service marks, trademarks or registered trademarks of API in the United States and/or other countries.

wellsite, this existing surface is pro- emptied soda bottle. The feld induces 2013. Production strategy was to main- vided by pipe, valves, and other internal nucleation of gas bubbles and the fuid tain original choke setting for two weeks.

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