Nearly 70% of the oil production today comes from the mature fields. However, the development of mature fields is faced with tremendous financial and technical challenges. Nevertheless, 80% of oil comes from 20% of highly productive wells – which means pinpoint drilling of sweet spots, together with customised reservoir development strategy, can achieve the commercially competitive production at a fraction of the initial cost. To achieve so, accurately locating the remaining oil has become the key target for the asset subsurface teams.
Locating remaining oil: a different mindset at mature fields
At mature fields, asset teams usually have gained adequate knowledge about the reservoir stratigraphic structure, geologic background with reasonable development plans. The business and technical goals are different at this stage of field life compared to the work in prospects and green fields.
Table. Different business and technical focus in green and mature fields.
Directly monitoring the changes in the subsurface requires confident acquisition of field data, such as 4D seismic, tracer data, with systematic interpretation skills. Practically, this involves the strategic value of the advanced technology from the organizational level with a large amount of R&D investment and exercises. The mature skillsets are currently owned by major players only with limited access and acceptance for the smaller players.
Accurate modelling and prediction of remaining oil distribution rely on a solid understanding of the reservoir statics and dynamics in reservoir models. Achieving so means a good master of the reservoir mechanism based on the accurate depiction of static reservoir property distribution and dynamic production schemes. However, the static reservoir is usually modelled at the early stage of field life, with workflows that are usually built for different purposes (stay tuned for the coming article on fit-for-purpose modelling). Nevertheless, modelling of the dynamics is only achievable when the static reservoir model is detailed enough, with workflows that are open to frequent updates to cooperate the daily increasing amount of field data.
Optimum well locations. New wells are primarily determined manually in the industry. Computer-based optimization is very computationally expensive. It takes months to test over all the drilling target candidates which cannot meet the business decision timely.
Three solutions to locate the remaining oil
1. 4D monitoring and interpretation.
Interpretation of the 4D seismic data requires systematic planning and implementation. Practically, a hierarchical approach is proven very useful to utilize the 4D data. Prior to the acquisition, a feasibility study is essential to validate the value creation. To make sense of the data, firstly, 4D seismic should be tied to the production data by screening through the production history and selection of appropriate 4D attributes.
Dedicated 4D rock-physics calibration is essential to bridge between the reservoir and seismic data. Depending on the frequency monitoring surveys and quality of the seismic data, well-to-seis and 4D oriented Inversion technologies can be applied to strengthen the noise ratio and back out reservoir engineering consistent solutions. In addition, more quantitative studies can delineate the effect of pressure and saturation based on the seismic and engineering data.
2. Model re-conditioning
At this stage, you should move one step further than the conventional reservoir modelling workflows to introduce the subsurface realisticity to the reservoir models by “closing the loop” between reservoir model, 3D seismic data, 4D seismic data, well logs and production histories. 3D&4D Closed-loop reservoir modelling workflow is a dedicated way to
- Directly extract the static reservoir properties from 3D seismic
- Improve the static seismic match of the reservoir model to 3D seismic data
- Quantify the 4D changes of the reservoir using unique coupled 4D inversion
- Matching the dynamic behavior of the reservoir model to the 4D seismic
3. Comprehensive well placement/production optimization
With reinforced accuracy and predictability in your reservoir model, it’s time to answer the engineering question by realizing the drilling potential. A qualified solution should be able to answer you the following questions:
- How do your wells look like? Vertical wells? horizontal wells? Sidetracks? Geometry? Perforations?
- How many more you should drill? More wells DO NOT guarantee better economic returns. Your solutions should be smart to answer this given your budget, financial expectation, and engineering tasks.
- Will you have your answer in time? This is critical based on our hands-on experience. Most of the R&D algorithms do not help in practice because they don’t deliver timely, regardless how mighty your computer is.
In a nutshell
The mature field is the key to industry and locating the remaining oil is winning. Dedicated solutions are necessary and it is different from conventional tasks.
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Author: Dr. Sean Tian,
EVP of iRes-Geo, Formerly Reservoir Geophysicist, Chevron Global Technology Centre, Aberdeen
Ph.D. in Reservoir Geophysics from Heriot-Watt University.