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.

Clearly delineating contacts are usually aimed at before development, but what happens when later data indicates contacts different from what have been interpreted? How do we ‘work back in time’ to re-estimate the original contacts? Our case study documents a reservoir which due to the poor well coverage, paucity of log data, side wall sample and pressure data, was initially interpreted as an oil bearing reservoir, however, a new well drilled post production of over 20 years indicated the presence of a huge gas cap, the size of which could not have been due to the formation of a secondary gas cap. This necessitated the determination of the original contacts in order to properly define the reservoir volumes which will impact on its future development. This paper presents the use of an integrated thinking approach which makes use of all the available geological, petrophysical and dynamic data in determining the original fluid contacts in a post production scenario. Reservoir simulation using simple tools as material balance combined with petrophysical and geological concepts were applied in this paper. The results obtained shows that the use of static data alone such as petrophysical logs in determining the original contacts for post production reservoirs can be greatly misleading as the results obtained may conflict with dynamic data available for the reservoir and therefore not fully representative of the reservoir and its history.

The significance of pressure transient analysis has grown over the years, as it has become a key source of subsurface information needed both for surveillance and effective reservoir management. However, it could be quite challenging especially in complex analysis and having an interpretation representative of the reservoir system could be daunting amidst widely varying uncertainties, data quality, limited geological and engineering data. It is therefore quite imperative that the analysis and interpretation approach be robust enough in order to give information that is representative of the reservoir in consideration. While the objectives for acquiring well test data in the first place varies over the life of a field, the interpretation methodology remains practically the same and it is the focus of this paper to give a more practical approach to PTA interpretation for a field at its developmental stage and help resolve one of the problems associated with PTA interpretation which is having a well defined, logical and consistent interpretation approach across different interpreters. This paper presents the application of a divergent thinking approach in well test analysis using multi scenario modeling and then following logical steps using all available geological and engineering data to converge to the most likely interpretation. The application of this approach is discussed using three different fields in the Niger Delta region of Nigeria as case studies which have been carefully selected from a field with little less than 2 years of consistent production (relatively new) to fields with an average production of about 25 years to reflect different level of understanding of the reservoir system based on available data. Analysis was carried out on well test data acquired from these fields using SAPHIR software by KAPPA. The results obtained show that regardless of what model were chosen, a relatively good model match can be obtained for the available data and except all available geological and engineering data are applied in an integrated manner, a non-representative model can be chosen for the said reservoir further leading to more uncertainties.