Independent industry analysts have assessed the economic impact of 4D seismic in the North Sea and concluded that since 1996 4D surveys have resulted in:
- added value of more than $4 billion
- greater than 6% reduction in drilling costs
- significant improvements production forecasting
- additional reserves averaging 5 percent per field
In general, field economics can be improved by accelerating production, increasing or extending plateau production rates, reducing the rate of decline after plateau, or extending field life to delay abandonment. A new well, properly placed, can achieve all of these benefits, although the plateau production rate is often limited by external constraints and is thus not changeable. If poorly placed, the well may encounter high water saturation immediately, or it may water out rapidly, for example. Given the resulting range of possible economic outcomes, information such as 4D measurements that help to guide well placement can have a significant, and quantifiable value.
Avoiding poor well placement4D results can prevent poor well placement by assessing the state of the reservoir at a planned well location. If oil has been produced from the location, or soon will be, it would not be an economic location for the well. The value of this 4D information is saving the cost of an unnecessary well. In areas in which the cost of drilling wells is greater than the cost of a 4D project, this alone can be a significant impact.
Optimizing placement of new wellsWhen 4D results are used to plan a new well location, it is possible to optimize the placement of that well. When undrained compartments are identified by 4D technology, one can locate a well within the compartment to access the additional reserves. Alternatively, wells can be located away from advancing fluid fronts and/or protected from fronts by natural flow barriers within the field. By doing so, it may be possible to extend plateau production or decrease the decline rate after plateau. View
case study.
Locating undrained reservoir compartments When 4D results indicate no reservoir change in areas expected to be in production, it is likely that those areas are isolated reservoir compartments. This represents oil that may have been booked as recoverable, but will not be recovered with the current well pattern, resulting in a shortening of plateau production and lower ultimate recovery. By locating the compartment, 4D surveys quantify the lost reserves and allow placement of a well to access it.
Identifying drained areas/fluid frontsLocating drained areas and fluid fronts with 4D methods gives a direct indication of the flow units in the reservoir. With this information, it is possible to anticipate early breakthrough, potentially in time to adjust field production rates to prevent breakthrough from occurring. This information is also important for locating new wells away from fluid fronts to extend the plateau and accelerate production.
Reducing uncertainty in reservoir modelsReservoir models always contain a degree of uncertainty, but 4D results can reduce some of that uncertainty. As a spatial measure of fluid movement, 4D provides unique information that can be used to constrain the generation and selection of reservoir flow properties. With less uncertainty, there is less risk in many reservoir development and production decisions, which could result in accepting rather than rejecting an economically viable project.
In practice, most reservoirs will benefit from 4D projects in more than just one way. When predicting the value of 4D projects for the purpose of deciding whether to do a 4D project, only the largest anticipated benefit would be considered, even if it is recognized that 4D results could, say, both aid the selection of well locations and identify compartments containing additional reserves. This is a conservative approach to valuing 4D information, but one that almost guarantees that the benefit from 4D technology will be greater than originally predicted.
Quantifying economic impactInformation has economic value if it can be used to increase the monetary return to the company, reduce the risk in making a decision, or both. While it is usually straightforward to quantify the value of expected increased production, for example, it can be difficult to quantify the economic value of reduced risk. A decision tree (see top figure to right) is a tool with which both aspects can be evaluated at the same time. Broadly termed the value of information (VOI), the VOI of 4D (V4D) technology is a risk-weighted estimate of the business value (difference in expected monetary value) that could result if a 4D project were undertaken.