Delving into dynamic modelling

Patrick Calvert and Peter Griffiths, BP, UK, explain how dynamic flow modelling has created a powerful insight into operations, leading to higher production rates and reduced operational risk.

Sustaining production from wells that are reaching maturity has traditionally been a significant challenge for operators looking to maximise the recovery from a field. In response, there is a growing need to improve the understanding and management of dynamic transients that strongly influence process operability and the overall recovery factor from the field. For example, optimising the dynamic transients can mark the difference between a successful and an unsuccessful well start-up and, when in production, optimising flow stability will reduce the need for excessive choking, thereby providing a stable platform to push production closer to capacity.

Fluid conditions experienced during well start-up, liquid loading and slugging are sufficiently removed from the steady state to render steady-state-modelling tools ineffective at simulating the associated behaviour. As dynamic transients have become more challenging to manage, dynamic modelling has received more recognition amongst petroleum engineers. Software, which has historically been confined to the flow assurance community, has been rapidly extended to address this growing demand.

Starting with a single project on a platform in the North Sea, BP’s dynamic modelling programme has grown to encompass six separate regions. In 2011 dynamic modelling and control accounted for 17 500 bpd of the company’s annualised incremental production.

Dynamic modelling

Initially, BP modelling activities were limited to low rate wells and flowlines that experienced stability or start-up problems. However, the scope was extended to include high rate wells where rapid transients can have significant safety implications. Figure 1 highlights a series of operating problems that dynamic modelling has proved effective at addressing.

Figure 1. The flow conditions that give rise to a range of transient operating problems.

Within Figure 1, each challenge has been framed in terms of the superficial liquid and gas velocities, which represent the flow conditions that give rise to the problem. Two areas where BP has seen significant demand for dynamic modelling are well start-up and well clean-out.

Start-up can be problematic in wells with poor pressure support and no artificial lift. If the pressure driving force across the well is insufficient to overcome the maximum hydrostatic head experienced during start-up, any attempt to bean-up the well will fail. The amount of water or dead-oil present within the well will increase for each failed attempt, impacting subsequent start-up attempts. The operating strategy for such wells is critical, as the manifold pressure needs to be sufficiently low to ensure a successful start-up. Dynamic modelling has assisted in providing an understanding of the shut-in pressures required for a successful start-up. By combining commercial modelling software with simple data analytics, an optimum bean-up rate can be determined for each well along with an estimation of the time it takes for the well to unload. To date, the use of well start-up guidelines derived from dynamic modelling has proved critical in the continued production from a number of fields in the North Sea, the Gulf of Mexico and Trinidad.

The ever-increasing rigour required for operational decision-making meant that it was a natural progression to apply dynamic modelling to support drilling activities. Dynamic simulation has helped in the understanding and fine tuning of the steps required to ensure the complete removal of mud in an environment that is constrained by the rate of produced fluid and the total volume of fluids that can be handled during well clean-out operations. Having the in-house capability to model clean-out operations has led to a much stronger collaboration between design teams and the technical contributors. The HAZOP review has been particularly strengthened, and simulated flowing temperatures and pressures have formed a vital feed to this process. Questions and scenarios raised during the HAZOP can be appropriately simulated to provide the information required to complete any remaining actions.

Building a sustained offering

Over the past six years, the company has adopted a three-tiered approach for developing and sustaining dynamic modelling through a process of demonstrating value, crystallising interest and building regional capability.

The creation of an internal dynamic modelling programme was followed by the establishment of pilots in three North Sea fields through collaboration between the central subsurface technology organisation and key staff in the region. The combination of third party applications and in house software enabled the company to create an improved operating strategy for each field, bringing enhanced flow stability and increased production by 3500 bpd. With few practitioners it was also necessary to express the output of the modelling in a manner that could easily be interpreted by those with no previous experience of dynamic modelling. Visualisation was used to convey the key findings derived from the dynamic studies. Particular emphasis was placed on presenting the findings in a format that preserved the ‘shelf-life’ and recognised the synergy between steady state and dynamic modelling. The latter ensured that dynamic modelling could be tied in with an extensive group of steady state modelling practitioners.

Other influential factors in the success of the pilot included buy-in from the assets involved and the company as a whole, continuous remote support, easy access to real time operating data, the ability to refine and hone the modelling techniques and a clear understanding of the value that the modelling added.

The success of the three pilot schemes in the North Sea encouraged the company to appoint a full time modelling specialist for the region. A single modelling programme was developed from the pilots, which could then be coordinated entirely from within the company’s North Sea business unit. This initial development in the North Sea, whilst demonstrating success, was also designed to ensure the concept could be replicated in many other regions. An active dynamic modelling programme is now present within Angola, Azerbaijan, Trinidad and the Gulf of Mexico.

Over a three-year period, the resource level has grown in line with the value delivered. Modelling teams have been established within the North Sea, Azerbaijan, Gulf of Mexico and Trinidad to support the modelling activities regionally. The success of each team has led to significant internal buy-in and growth in the modelling work and the value delivered. Each team has a clear remit. The modelling knowledge is shared amongst the individuals and the modelling software and workflows have been standardised.

Conclusion

What was initially a relatively small, regional pilot project for BP has matured into a global initiative across the company. The number of fields involved in the programme has increased leading to a significant gain in incremental production. Dynamic modelling has enabled BP to increase incremental production tenfold in the past six years. In 2011, dynamic modelling initiatives led to 17 500 bpd of annualised incremental production.

The company’s focus on demonstrating value and building regional capability, through effective application of technology and seeking to develop and standardise best practice, has enabled it to build a permanent capability for sustaining the use of dynamic modelling to support its daily operations.

Adapted by David Bizley

Read the article online at: https://www.oilfieldtechnology.com/drilling-and-production/24022014/delving_into_dynamic_modelling/