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WellModel - ftype

Hi everyone, has anyone coupled the Wellsim  wellbore simulator to tough2? as a f-type generator for example?

3 replies

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    • Reservoir Engineer
    • Alfredo_b
    • 5 yrs ago
    • Reported - view

    Marco,

    I used the f-type GENER option, but the BHP values in the rate-enthalpy table were not computed using Wellsim. I was using another numerical wellbore simulator called PROFILI. And it worked.

    The f-type option to simulate a well production at fixed WHP has two main limitations:

    i) it works only for a well producing from a single feedzone;

    ii) the BHP is computed with the wellbore simulator with a fixed fluid composition. 

    For geothermal applications the above limitations often cannot be accepted. For instance, most of wells produce from multiple feeds over quite long sections.

    To overcome the first limitation, I modified TOUGH2 by coupling the f-type option with a well on deliverability completed over multiple feedzones. The f-type option gives the BHP at the top of the producing interval, while the TOUGH2 standard well model computes the pressure gradient in order to evaluate the BHP in front of any feedzone. The code modification was working, but the results were acceptable only for wells with single-liquid flow in the  producing section.

    In fact, the standard TOUGH2 well model is built with heavy assumptions not allowing a proper solution of two-phase flow and dry steam flow (conservation of volumetric rates rather than mass rate; no flash calculations, but properties taken equal to that of fluids in the reservoir block; friction and acceleration pressure drops neglected, ecc.).

    Regards,

    Alfredo  

    • Marco_Cecioni
    • 5 yrs ago
    • Reported - view

    Hi Alfredo

    Thanks for your reply. I'm aware of the limitations and I agree with you. I was thinking, even if it not correct, to run a wellbore simulation with multiple fractures and then create one f-type table for each feedzone and treat them as separate source/sinks in tough2.

    The main asumption is that incoming enthalpy and mass flow rate aportioning (for each feed zone out of the WH flow rate) will be the same for every escenario. This is clearly is not correct since enthalpy will not be the same in each fracture and flowrateswill change the accordingly with with the mass that is coming from below and it respectively BHP. Do you think it will a good aproach? 

      • Reservoir Engineer
      • Alfredo_b
      • 5 yrs ago
      • Reported - view

      Marco Cecioni 

      Marco,

      your problem is a classical one in which a coupled solution of reservoir and wellbore flow seems to be mandatory. Have you considered to use T2Well ? It could provide a coupled transient solution accounting for the actual discharge rate and enthalpy of each feed.

      The F-type options requires the simulation of wellbore flow at constant WHP, from the wellhead and for different rates and enthalpies. This is rather simple when you have a single main feed which is controlling the flowing P&T conditions.

      In your case you have multiple feeds, I imagine each one with its own PI, static pressure and fluid enthalpy  (or kh, Pres, fluid enthalpy, depending on the way the feed flow is simulated). When you simulates the wellbore flow at constant WHP and for different rate-enthalpy values, the discharge of each feed can change ramarkably depending on the conditions involved. Feeds can even reverse from production to injection at some extreme rate-enthalpy values. You could probably be able to derive the BHP table for each feed, but I think it will be almost impossible to understand which are the actual effects of the approximations involved.

      Then, when you run with each feed having its own BHP table, each feed will evolve independently from the others. Difficult to say about the reliability of results. I believe it will be very dependent on the specific case simulated.

      In the TOUGH2 version used in Petrasim (by Thunderhead Eng., see Battistelli et al., 2017, Stanford Workshop) an additional option has been included when simulating wells on deliverability completed on multiple feeds. The flowing wellbore pressure in front of each grid layer on which the wellbore is completed (the feeds) can be assigned as input parameter. These flowing pressures are computed externally using a wellbore simulator for the desired WHP and for total mass and mixture enthalpy that match those obtained with TOUGH2 following a trial-and-errore approach. The assigned flowing P are used instead of the standard well model available in TOUGH2.

      During the simulation the total rate and discharge enthalpy for each well are controlled. When they depart significantly from the original values, the simulation is stopped. A new wellbore flow simulation is performed with the new rates and enthalpies computed by TOUGH2 and the computed flowing P are used to restart TOUGH2. It is a cumbersome approach, but if a fully coupled approach is not available it is any way an improvement with respect to the original DELV option.

      I worked in the past on an improved DELV option to simulate the well discharge at constant WHP and with a rigorous simulation of wellbore flow (Marcolini and Battistelli, TOUGH Symposium 2012). The code was working, but its testing at the level required for a reliable use was not completed. This in particular for EOS2 and EWASG modules.

      Regards,

      Alfredo

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