Thermal Applications

 

Modelling Wells With Thermal Challenges

What Thermal Challenges Are Encountered in Wells?

In every producing area of the world, thermal challenges are encountered in the downhole environment.  Examples of these challenges include:

• wax formation
• hydrate formation
• freezing of water across downhole chokes
• high oil viscosity limiting well productivity

One of the best methods of understanding these challenges and developing viable solutions to the problems they present is to accurately model the thermo-hydraulic performance of the well.  WELLFLO, Neotec's well flow modelling software, is recognized as one of the most reliable tools available for such efforts, particularly when understanding flowing temperature profiles is important.

Electrical Heating

In addition to heat transfer calculations for production and injection wells (including steam injection applications), WELLFLO incorporates several specialized calculations that can be used to evaluate advanced applications for the mitigation of thermal challenges such as those noted above.  Once such calculation is the inclusion, in the overall energy balance for the production (or injection) system, of an external source of heat (i.e. energy).  Since 2004, Neotec has used this capability on numerous projects through a close working relationship with Tyco Thermal Controls, the world's leading provider of complete heat management solutions.  Through this relationship, Neotec has conducted modelling studies of more than 40 applications of Tyco Thermal Controls' electro-thermal heating systems for downhole and bottom-hole applications.  These projects have addressed a wide range of thermal challenges (including all of those noted above) and encompass all of the world's producing regions (i.e. North and South America, Europe, MENA, Asia Pacific, West Africa, etc.) in both onshore and offshore environments.  Common applications would involve the direct application of electrical heat to increase the mobility of oil or mitigate the risk of wax or hydrate formation.  More complex systems have involved combinations of downhole heating and artificial lift (downhole pumps and/or gas lift).  One case in Western Canada even investigated the potential for the combination of downhole heating and cyclic steam stimulation in order to extend the duration of the production cycle.

The figure below illustrates the influence that even moderate amounts of electrical heating can have depending on the specifics of the well involved.

Details of one remarkable example of the application of this technology were released by Tyco Thermal Controls in March of 2009.  At this time, production had commenced from two wells in the Maari field that were completed utilizing PetroTrace® STSi electric downhole heaters.  The following is an excerpt from the Tyco press release posted on their website: 

"Located in the Taranaki Basin, the Maari field is approximately 80km south east of New Zealand's north island, in ca. 100 meters water depth.  Field development consists of a wellhead platform tied back to a floating production, storage and offloading vessel moored nearby.  It is anticipated that the 5 heated production wells will average 35,000 barrels of oil per day once full production has commenced."

Neotec has worked with Tyco Thermal Controls and OMV New Zealand, operator of the Maari field, over a period of years to support their efforts to design an optimal downhole heating system to be used for flow assurance in the Maari field.  The principal objective in this case was to mitigate the risk of wax build-up in the wells' production tubing.  The resulting system "consists of 2100-meter skin-effect coiled tube heaters installed within the well's production tube for maximum heat transfer."

Julie Ahner of Tyco Thermal Controls refers to this as "an exciting time when technological advancements allow development and [improved] production in challenging oilfields that would have been considered non-viable in the past."

Neotec is pleased to have played a role in the advancement of the Maari field development and is proud of our continued cooperation with Tyco Thermal Controls in providing clients with the best possible solutions to complex thermal challenges that benefit from the application of downhole heating systems.

Circulating Fluid Heat Transfer

Another unique capability of WELLFLO is the ability to model circulating fluid heat transfer.  This is another technique that allows the operator to add energy (i.e. heat) to the fluids in the downhole environment.  To do this, a second tubing, the circulating string, is run into the annular space between the production casing and production tubing.  This is shown in the simple well diagram at the right; the circulation string is marked in red and the annulus is marked in blue.  The heat source will be a fluid, commonly water, glycol, or diesel oil that is heated at surface and then circulated through the system.  Most commonly, the hot fluid is injected down the circulation string and returns to surface in the annulus, but it is also possible to circulate the fluids in the reverse direction.  The hot fluid circulated in the well thus forms a temperature bath for the produced fluids which may, at different depths in the well, draw heat from the produced fluid or add heat to the produced fluid.  The complex interaction of the injected hot fluid, the circulating fluid returning to surface, the produced fluid, and the surroundings can lead to some very interesting temperature profiles.

An example is shown in the plot below.  In this case, the hot fluid enters the circulating string at 60°C, cools to about 31°C, and then reheats slightly near the bottom of the circulating string.  In the return annulus, the circulating fluid continues warming to approximately 32°C, before cooling about 24°C and then being re-heated to approximately 28°C.

Heat Transfer Validation

In one recent study of a complex heat transfer application, the client required the validation of WELLFLO's thermal calculations before they would consider its application to their field issues. The client provided detailed well data for three wells in the field and requested that models be constructed and compared with data measured during initial production test of the three wells.  The average difference between the measured and calculated temperature profiles for the range of data evaluated for the three wells was less than 4%.  This accuracy was more than sufficient to convince the client that results from WELLFLO could be relied on in determining the best available solution for the thermal challenges they were facing in their field.

Once again, Neotec is proud to have proven the accuracy and performance of our WELLFLO software.  WELLFLO has been in uninterrupted commercial use since 1976 and continues to provide proven, accurate results for both standard wellbore applications and more exotic, leading-edge advancements.

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