BRAMLETT, KENNETH W., and CHRISTOPHER S. LERCH, Shell Deepwater Development, Inc.

Abstract: Reservoir Management of Deepwater Reservoirs: How to Optimize Their Performance

Approaching the next millennium, geoscientists and engineers are faced with developing deepwater oil and gas reservoirs with fewer wells which leads to greater uncertainty. Successful development requires that these few wells obtain high rates and high ultimate recoveries. High capital costs will require rapid depletion of reserves, leaving little chance for phased development.This increases uncertainty and risk in that learnings from one phase cannot be applied to the next phase. In order to achieve the necessary rate and recovery, horizontal wells with long lateral penetrations and multi-lateral wells will become common. Most wells will have large tubulars in order to achieve acceptable rates.The primary impact of fewer wells is the general increase in the uncertainty in which development decisions must be made. This is especially true in relation to estimating reservoir connectivity and reservoir recovery efficiency. Total in-place volumes will be more difficult to discern as we move under salt and into greater depths with no seismic amplitude supported.The main question is therefore,"How are project development teams going to be successful in this difficult technical and price environment?

A combination of technical and decision-making tools exist which can help in this regard! First, reservoir development teams must migrate from a single static reservoir model to multiple scenarios which can capture a realistic range of uncertainty. Scenario planning allows development teams to focus on key uncertainties and plan development in a manner that maximizes the chance of success. Scenario planning also promotes appropriate data acquisition that can help narrow the range of uncertainty. It also helps decision quality since an array of scenarios are considered.

One example of multiple scenario static modeling is the application of several stratigraphic connectivity models for the internal reservoir architecture. These can be derived from outcrop data (connectivity curves), internal boundary scenarios, and analog field architectures. A second static analysis technique is seismic inversion. If the reservoir is amplitude supported on seismic data, this can be particularly successful, especially model-based inversion. This method allows the testing and updating of a predictive impedence model(s) against the actual seismic data.

Once a field is producing, several techniques can be employed in order to model the reservoir dynamically. Many of these techniques have not been widely available in the past. The growing use of permanent downhole pressure gauges provides an abundance of information that can be used to almost instantaneously analyze reservoir and well performance. Analysis of reservoir barriers with their response to production is a significant positive aspect of acquiring these data. Additionally, once multiple wells are available, there is continuous interwell pulse testing which aids in interpretation of architectural connectivity. The abundance of pressure buildup data also allows rapid modifications to the volumetric estimates from material balance.

Seismically, the advent of 4D seismic allows modeling of areal reservoir drainage. Using impedence models (developed for inversion), the development team can first predict the feasibility of 4D seismic as a tool. The drainage predictions from modeling and simulation can be tested and modified as 4D data is acquired. This helps not only identify bypassed oil but also.helps to confirm or refute the accepted reservoir model which leads to better reservoir management. Cross well tomography is a technique that has seen limited application due to equipment limitations. However, cross well work in conjunction with permanent downhole pressure monitoring and 4D seismic is expected to contribute to a significant reduction in uncertainty in many fields.

Geochemistry is another method that has proven valuable and needs to be better utilized, especially in view of the relatively low cost. Oil and gas similarity analysis provides information on reservoir connectivity. Although not a precise indicator of compartmentalization, isotope variance can be a distinctive indicator when combined with other sources of data.

All in all, there are many tools which can be utilized in the task of optimizing reservoir management. The combination of scenario analysis, rapid model updating, and incorporation of production performance information should lead to more effective data acquisition and more efficient reservoir development programs.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England