Whether it is wireline or coiled tubing, hydraulic workovers or slickline units, well intervention is a key element in optimizing oil and gas production today.

The last few years have also seen a step-change in well intervention technologies — away from expensive, full size mobile drilling units toward lightweight, subsea well intervention systems where intervention can take place without a riser to the surface.

The Norwegian Continental Shelf is one region where light well intervention is increasing field

Software allows rapid reservoir model updates to match true production to reservoir potential. (Graphic courtesy of Roxar)
recovery, reducing costs and improving safety as it no longer requires transportation of hydrocarbons to the surface. There are also strong potential cost savings, with smaller ships rather than large mobile installations being deployed to carry out interventions.

Yet well intervention — whether it is more traditional or “lighter” — is still not the panacea to all flow assurance problems. Riserless intervention, for example, remains restricted to low depths, and sometimes operators tend to ignore issues such as pulling a subsurface safety valve, for example, just because of the costs involved.

And as subsea production extends into deeper fields in more remote regions and high-pressure/high-temperature (HP/HT) environments, the idea of costly well intervention systems becomes distinctly unappealing to the operator.

The “World Deepwater Market Forecast 2006-2010” from Douglas Westwood estimates expenditures on deepwater operations will reach more than US $20 billion by 2010.
This article will argue that much well intervention can be avoided through proactive, preventative and real-time monitoring of the reservoir and downhole wells. Through this, perhaps a smaller proportion of that $20 billion will be spent on well intervention technologies.

Getting into trouble

One of the key reasons for well intervention projects getting into trouble is when they lack accurate downhole information and the ability to carry out preventative and remedial action based on real-time information.

For example, attempts to replace completion components and free up wellbore access could be prevented if early monitoring systems had highlighted the sand in the well stream. The same goes for pipeline corrosion, which is often the result of unchecked water in the production flow.

Furthermore, many operators today only have a limited understanding of the pressures and temperatures being exerted downhole and the impact this could be having on equipment. The result is that sometimes well intervention, such as logging, perforating, plug setting and pulling, takes place unnecessarily and, at other times, when it is too late.

Two stages that can mitigate requirements for well intervention are at the well planning and field development stage and during the real-time monitoring and production stage.

Well planning, field development

Decisions made during the well planning and field development stage can have a significant effect on future requirements for well intervention and on the future productivity of the wells in question.

Take well planning, for example. Effective well planning ensures that the well is built in direct interaction with the geological model and within a shared earth model — a single model of the reservoir that incorporates all the observed and interpreted data.

Multilateral wells, sequential target wells and wells with geological or technical sidetracks can be planned and a survey program can be specified to evaluate the position uncertainty of the well path, relative to horizons or faults, for example. Safety margins will also need to be respected with neighboring wells.

In addition, a major challenge when planning wells is integrating geological and drilling engineering constraints to reduce uncertainties to minimize drilling risks and reduce planning iterations.

This was demonstrated on a recent North Sea project in Lower Cretaceous turbidite sands where Roxar’s well planning tool, RMSwellplan, was utilized after attempts to build a horizontal well across internal shale barriers had led to the hole collapsing, resulting in the loss of the horizontal section.

Using the company’s modeling software IRAP RMS to assist with the planning of a new horizontal well, a new model was developed which included newly interpreted faults as well as several facies models built to assess the lateral variability barriers.

Several different well strategies were planned to allow for the maximum reservoir sand contact while retaining well stability. And to help reduce the planning cycle time, the well targets and trajectories were designed directly into the model with the planning tool.
The result was a robust, intelligent well design and enhanced wellpath quality, likely to lead to less well intervention requirements in the future.

Field development planning

Although the value of wells tends to be realized during production, the decisions about the use of smart well technology have to be made during the development stage, in particular during field development planning where the maximization of net present value (NPV) needs to be established.

It is at this stage that reservoir engineers, production engineers and well engineers need to sit down together and ensure that everything from the 3-D reservoir modeling to reservoir characterization and uncertainty analysis, reservoir simulation, production engineering and artificial lift analysis are fully integrated and coordinated.

While well and field development planning has an important effect on future well interventions, it is the real-time monitoring of the reservoir and information on the fluids flowing through it that can have the most dramatic effect on well intervention requirements.

Real-time monitoring

The need to monitor well operations more closely has increased with the growing use of extended designer wells with multiple production targets, or multilaterals with several branches.

Real-time monitoring can be achieved through a series of components that collect and analyze completion, production and reservoir data and where the contribution from each producing zone is closely monitored to help optimize production but without the need for physical intervention.

This can be achieved through a new intelligent well interface standardization-compliant intelligent downhole network (IDN) — a complete sensor system for downhole production surveillance.

Operators are able to install up to 32 instruments on a single cable with no interdependence between the measurements. The downhole sensors are then placed between each production/injection zone and are utilized to monitor temperature and pressure.

Well control by permanently installed sensors across each individually perforated zone of a multilayer well provides a cost-efficient alternative to logging operations.

In the future, taking multiphase metering downhole and increasing the operator’s information on not just temperature and pressure but also sand rate, water cut, gas fraction and flow velocity will also be an essential part of real-time monitoring.

In this way threats to production can be detected by the multiphase meter and then pinpointed by the downhole sensors. For example, if unwanted water or gas enters the well bore, the multiphase meter detects the change in multiphase composition at the subsea well head. By examining the real-time information from the downhole pressure and temperature gauges, the operator can locate the problem area for remedial action.

Actions such as injecting water or gas into the reservoir for improved sweep efficiency can also be closely monitored with the injection rate in each individual reservoir layer being closely controlled. In this way, many of the causes for well intervention can be mitigated.

Acting upon the data


Accurate reservoir monitoring can only be successful if the production information is incorporated as quickly as possible into the reservoir model and then acted upon.
To this end, a company should look further than “what-if” analysis and use the right-time data to rapidly update the reservoir model, thereby driving downhole control devices and wells equipped with valves and chokes in real time.

In this way the remotely operated valves placed in the reservoir and actions such as the choking or shutting off of different zones can ensure that the well characteristics change instantaneously, which can then be reversed or repeated as many times as desirable.
This is what the true vision of the smart well should consist of, offering up an alternative vision to well intervention, which can be expensive and not easily reversible.

A last resort

No one can claim that properly targeted well intervention is not a crucial means of optimizing production and enhancing oil and gas recovery.

The benefits of effective well planning and real-time and actionable monitoring are, however, helping to close the reservoir and production data loop and ensure that well
intervention is a last resort rather than an integral part of reservoir management.