Over the past few decades, oil and gas operators have been able to increase production while lowering costs. Their greatest interest and investment has been focused on the early life of a reservoir – its productive heyday; however, times are changing. Global oil demand continues to grow and, while there are ample reserves, the geology of recently-discovered reservoirs is becoming more complex, while physical access to these reservoirs is more challenging than ever.
Technology developments and improvements in process efficiency are making such fields increasingly viable, but exploitation of these new reserves is not a short-term response. As a result there is a renewed focus on older plateau fields and sustaining their production for as long as possible. Brownfields – defined as mature fields in a state of declining production or reaching the end of their productive life – form a significant part of exploration and production (E&P) companies’ portfolios. The majority of world oil production now comes from fields more than 30 years old, whose recovery factor currently averages only approximately 35% to 37%.
To enjoy profitability while meeting increasingly complex production challenges, E&P companies are leveraging new technologies, exploring process changes and partnering with service providers in innovative ways.
Schlumberger made a commitment 25 years ago to actively address these brownfield challenges, particularly in the area of risk and cost reduction. Our experience has shown that improving recovery from mature fields requires an application of practical and focused engineering coupled with the introduction of new technology. Most importantly, it requires specialisation.
Managing Production Decline
The maturing fields in North America have taught us that unlimited capital expense cannot reverse decline. While technology without expert direction and careful selection should not be considered a panacea, the technologies needed to slow, halt or reverse production decline fall into these categories:
- re-evaluation of reservoir;
- remediation of wellbores and facilities;
- efficiently targeting bypassed or undeveloped reserves;
- production optimisation, particularly completion and lift strategies; and
- fluid management in general, including water management.
Re-evaluation – Understanding the Big Picture
A key part of field re-evaluation is to understand the current state of production. Advances in resistivity logging technology have improved cased hole formation evaluation and have also demonstrated remarkable results in detecting fluid behaviour in declining reservoirs.
A cased-hole formation test tool with success rates in excess of 95% is being used to obtain multiple samples in a single descent and to identify bypassed resources, such as oil swept to another part of the reservoir as a result of waterflood.
Production logging technology is used to analyse current well and reservoir production and identify opportunities for improvement.
Real-time information can make a significant impact on all technical areas and is helping to extend the peak of production. Technology enhancements enable correct on-the-spot decisions and solutions involving integrated cross-disciplinary services. Remote monitoring devices and information systems offer the option of understanding what is taking place in the reservoir and the ability to take corrective action in real-time.
Remediation – Infill Drilling and Recompletion
Reservoir management provides a better knowledge of fluid distribution in the reservoir. This in turn means that highly effective well profiles can be planned for infill drilling. Advanced imaging techniques allow the operator to select the best locations for infill drilling to optimise well placement and to apply new cost-effective drilling methods.
Better steerability, dogleg capability and slimmer tools have been developed to drill technically difficult wells, e.g. complex trajectories to intersect as many target zones as possible or to reach one ‘sweet’ spot.
Specially designed seismic apparatus are being incorporated into new drilling technology to allow better formation imaging while drilling. The logging suite delivers crucial real-time data for evaluating the positioning of drilling strings and modifying the well path as needed.
Particularly useful in mature reservoirs where pressure has been a long-standing challenge is a new perforating system that controls an optimum dynamic underbalance reservoir pressure. New techniques minimise disruption of the cementsandface hydraulic bond and create optimum perforation shape and length.
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