In petroleum industry, the development of oil resources is performed under strong uncertainty conditions, not only related to the geological and reservoir characterization, but also concerning the economic parameters. Depending on the number of appraisal wells drilled at the time of the decision, we may choose to start the execution of the development plan, or to pay for more information. This includes the realization of a new seismic acquisition, the drilling of anew well, or the execution of pressure tests.
In the present work, we applied a value of information analysis, under uncertainties conditions, to optimize the exploitation of a new block in a deepwater field, located in Campos Basin, Brazil. The reservoir rock consists on high permeability sandstone, with good lateral continuity, without internal sealing faults. The most important properties that impact the volumetric uncertainty are the net to gross relation, and the position of the oil-water contact. Equally, the dynamic parameter that strongest affect the recovery factor are the absolute permeability and the well productivity. In order to simultaneously study the geometric and dynamic uncertainties and minimize the number of simulation runs, we performed an experimental design process.
The calculated economic value of the information from the new well, which results essentially from the optimization of the exploitation project, was much higher than its cost, recommending for its application. In contrast, the anticipated production did not show to be advantageous, and was discarded. Based on these results, the new well was drilled, and the reduction of the volumetric uncertainty permitted to implement a sharper design to the exploitation project.
Introduction
Offshore development projects require a great amount of investment. Another characteristic inherent to all E&P projects is the high uncertainty associated to these projects. Thus, there is a high risk associated to offshore production development projects. It is always a hard decision whether to gather more data and consequently postpone the production or start the development of the field with the information existent at the moment.
Recently, a wildcat discovered a new area in the ring fence of an already developed field. The data available in the area consisted in the well data(test data, logs, RFT, fluid samples) and a 3-D seismic survey. Although a reasonable amount of data existed, a lot of uncertainty remained, especially regarding the position of the water-oil contact (WOC) and the total pore volume of the reservoir. It was decided to do an analysis of the value of information of drilling a new well before taking any decision about this area.
A 3-D flow simulation model was generated and an uncertainty analysis was made using experimental design techniques1. Experimental design is avery well established statistical methodology to assess the space of variation of a given process due to variations in the input parameters of this process. The initial applications of this technique were laboratory experiments that took a long time to complete. In petroleum industry, the first use of experimental designs was also toward lab applications, but in the last 10 year sit is being used with great success in reservoir simulation to deal with uncertainty analysis and optimization cases2,3. The experimental design is followed by a linear regression of the results that is usually called response surface methodology (RSM). The RSM aims to substitute the original process by a faster function that will be used to generate the space of variation of this process.
With the results of the experimental design analysis and the RSM, the next step was to calculate the value of information (VOI)4. Only the drilling of a new appraisal well was considered in the VOI analysis. The VOI analysis was made with the help of tool called DSS5. This software combines decision tree and Monte Carlo simulation in a single package specialized in production development projects.
