A quick evaluation of reserves for new opportunities (e.g. perforation extension and other work over types) in reservoirs with distinct geological units and features is possible using a multi tank MBAL option. This saves time while still having results closely matching more detailed simulation models besides reservoir management due to subsurface uncertainties. In cases where a reservoir is naturally separated into units with the aquifer as the only common communication base or where there are constricting saddles which in production time allows preferential sweeping of the reservoir posits the possibility of separate tanks. Multi-tank MBAL has been used in this scenario to generate a production forecast for a work over opportunity in Reservoirs A, B & C. This methodology transmits the segregated accumulations of the reservoirs into tank sectors and connects them using transmissibility value to a common aquifer leg in a multidisciplinary approach. Resultant model is history matched and contacts calibrated prior to prediction especially when present contact information exists. The methodology as opposed to a single tank MBAL model gives better calibration of contact movement and forecast of the future and existing opportunities, thus giving credence to more robust reservoir management plan and resource volume estimation for the work over project. The MBAL multi tank methodology is a handy improvement tool for brownfield production forecast within the Wells, Reservoir & Facility Management domain especially where no 3D dynamic models exist.

A multi-tank model is presented that was used to evaluate the volume of gas produced from an undeveloped gas reservoir as a result of sand-to-sand juxtaposition with a developed oil rim reservoir. An innovative approach of using Microsoft Excel via OpenServer to link MBAL model to history match reservoir pressures in a multi-tank model, while considering all the reservoir uncertainties was adopted. The process helps to save time in Reservoir Management. An oil rim reservoir with future gas development seemed to be communicating with an undeveloped gas reservoir via sand to sand juxtaposition based on the pressure data taken during the drilling of one of the wells and fault seal analysis. This clearly showed depletion in the undeveloped gas reservoir. Through a multidisciplinary approach, the two reservoirs were built into tank models and connected using a transmissibility model. The resultant model was history matched using an experimental design approach and contacts calibrated prior to running simulation and prediction. The result showed the quantity of Gas Initially in Place (GIIP) in the undeveloped reservoir that has flowed into the developed reservoir and has possibly been produced already. This insight provides a quick analytical understanding on the resource volume impact of this phenomenon on both reservoirs with respect to their future gas development. This has led to the need for a revised development plan for both reservoirs with respect to future gas production. The novelty of the use of experimental design with MBAL multi-tank model in this scenario is in the ability to history match the model in reasonable time. This is achieved while effectively managing reservoir uncertainties. This is critical for key business decisions on reserves booking, business planning, general reservoir management and production.

Reservoir connectivity remains a critical and growing area of research and application in the petroleum industry, as most discoveries go through development to maturity. This becomes highly imperative for reservoir management decisions in highly fractured compartments or stacked reservoirs with faults across them. In most field cases and especially for a highly faulted region like the Niger Delta, there are some uncertainties around connectivity primarily due to seismic data and resolutions as regards the technology available at acquisition. The primary aim of this work is to use dynamic modelling to ascertain connectivity in mature reservoirs. This work applied the standard workflow for Reservoir Connectivity Analysis (RCA) in evaluating four (4) stacked reservoirs in the RAINBOW field, onshore Niger-Delta using dynamic modelling of the MBAL multi-tank option. Various scenarios were analyzed with the integrated data – geology, production and reservoir pressure history, fluid and rock properties to select the most likely scenario. For this analysis, a new diagnostic plot was introduced for evaluating transmissibility, which improved the clarity in decision making. Using the prevalent economic parameters, a quick evaluation was done to understand the impacts of the reservoir management decisions on the viability of this approach. From the results, two of the four reservoirs are observed to be dynamically connected. The analysis shows that a new perforation extension opportunity is a quick return decision that can yield considerable returns, while new infill opportunities as the optimal decision. Also, the effects of transmissibility on the reservoirs affect the Net Present Values of the decisions. Therefore, this improved workflow approach can be recommended as a quick win when sufficient time and resources are not available for opportunity maturation. Further work is also required to integrate this understanding to build a simulation model for robust benchmarking.

Uncertainty management for resource volume of a brown field is relevant. An analytical approach via dynamic model was used to evaluate this impact on a developed gas reservoir (brown) by two other reservoirs. One of them is a green oil-rim reservoir, while the other is a developed oil reservoir. This is due to sand-to-sand juxtaposition with the two reservoirs. Integration of available data over time, while considering all the reservoir uncertainties was adopted. This was buttressed by the continuous production from the gas reservoir, that had already gone past the initially evaluated Gas Initially in Place (GIIP). The brown reservoir is a highly faulted gas reservoir with twenty-seven (27) years production history, by seven wells. The reservoir's GIIP re-evaluation had been done twice over the years. This was because it had fully developed its ultimate recovery, with three wells still producing. This GIIP re-evaluation approach could no longer be utilized, as it had very good well coverage. Fault seal analysis, pressure, PVT sample and log data taken over time reveal the likelihood of communication across the stacked reservoirs. A multi-tank material balance model (MBAL) was built via a multidisciplinary approach. The model was history matched using an experimental design approach that saved time and contacts were calibrated. The result showed the quantity of hydrocarbon in both reservoirs that have flowed into the developed gas reservoir. This provides a snapshot on the resource volume impact of the reservoirs with respect to their development and uncertainty management. Revised development plans and resource booking for the reservoirs are also study outcomes. This is relevant for business decisions on resource volume booking and reservoir management. This approach is a quick win within the Well, Reservoir and Facility Management (WRFM) workspace. Further work by building a 3D simulation model and pressure data acquisition is required for robust benchmarking.

The primary focus of a wells, reservoir and facilities management team is to guaranty shareholders value by improving production and optimize recovery. Several best practices abound in the industry to achieve this goal. Some screening criteria are used during integrated field reviews to benchmark identified opportunities and rank/select viable candidates for execution. This screening criteria includes: economic ranking, reserves, doability and regulatory policies. The resulting unconventional study allows for a better reservoir management plan. This paper presents an integrated methodology utilized to restore oil production for a brown field via gaslift project. This was applied in the NAMUB Field case and the information obtained can be applied on other fields with similar scenarios. In the case of NAMUB field, the estimation of the incremental oil resource volume was estimated using Material Balance models that are calibrated with pressure data and history matched. The field did not meet up with conventional screening criteria for Gaslift Project. This is due to technical, non-technical and economic reasons. The field studied is composed of stacked reservoirs that have not had oil production for about ten years. Therefore, it was pertinent that a project had to be executed to restore/ carry out oil rim development. This was further made expedient due to the gas cap blowdown of the reservoirs. The continuous gas development impacted on the recovery of oil and further eroded oil resource volume. This integrated study comprised of Surface Engineering disciplines, Petroleum Engineering/ Geoscience disciplines, Economists and Business Planners. The outcome of inter-reservoir communication studies and sensitivity analyses was integrated to manage uncertainties leading to robust outcomes. The results obtained were not benchmarked against any previous one, as this was a unique step out scenario the company had to deal with. The performance of the 5 wells will be monitored against actual production to validate the methods and processes adopted in this study. The integrated approach used in the study across the diverse disciplines allowed for seamless delivery of the project.