This paper addresses the 4D seismic monitoring aspects of AKPO, a complex deepwater field operated by Total Upstream Nigeria Ltd (TUPNI). AKPO development is driven by seismic in many ways. Seismic reservoir characterization is critical for well placement, optimization and monitoring while drilling, as well as to delineate reservoir sedimentology, capture heterogeneities and pop ulate the geological model with rock properties. In addition, time-lapse seismic monitoring plays a key role in the understanding of the field dynamics, the update of the reservoir model and the field management as wells as the planning of the infill campaign. The first results of AKPO 4D monitoring program yield highly valuable information with great impact on reservoir management.

Adequate representation of reservoir heterogeneities in deep-water turbiditic systems presents a significant challenge in reservoir model building. Reservoir models are often too homogeneous, thus, making history matching not only difficult but sometimes less predictive and unreliable for long term production planning. In this paper we present a methodology to adequately capture and preserve variability in reservoir quality seen on well logs and seismic-derived reservoir properties inferred from 3D and 4D seismic. We demonstrate this technique in a deep-water field, offshore Niger delta.In the first segment of the paper, we show the use of time-lapse seismic (4D) to update seismic-derived facies proportion cubes. Such update ensures consistency between the predicted facies proportions and 4D results. We further present a workflow to combine well results and the updated seismic facies probabilities to produce a geologic facies proportion cube that preserves heterogeneities and respects all available data (well results, 3D/4D seismic). The methodology involves the use of weighting factors on 3D-propagated well data (reference cube) and the 4D-updated seismic facies proportion cubes (auxiliary cubes). We conclude the study with the use of seismic loop-back as a quality control tool to check the overall consistency of the static model petrophysical infilling with seismic-derived reservoir properties.We observed that most of the 4D-updated grid cells in the reservoir model are within the channel levees and lobe fringes, where seismic characterization might be less reliable but sometimes contributes significantly to oil in place (and reserve) in the field. The result highlights a useful application of 4D seismic for facies characterization in addition to reservoir monitoring. Also, the integrated facies proportion cube (well facies & seismic facies) not only retains known heterogeneities, it is consistent with 4D seismic. In conclusion, the seismic loop-back procedure, which involves the use of a calibrated petro-elastic model to generate reservoir elastic properties from model properties, shows that in most reservoir units in the field an overall good match was achieved between the reservoir model infilling and well data/seismic-inferred properties. In the field example, we observe that while a good match exists between the model and inverted parameters, nonetheless, important discrepancies have been found in areas lying mostly in wet channel levees. Careful analysis of such areas provides some insights about ways of improving the initial reservoir model infilling.The paper presents a unique technique to account for heterogeneities (in 3D sense) in reservoir models. It showcases a pathway to integrate and maintain consistency among well data, 3D and 4D seismic towards building a consistent, reliable and robust reservoir model.

This paper presents the innovative use of interference tests in the assessment of reservoir connectivity and the field oil production rate during the development phase and prior to the first oil of the EGINA field, which is located in a water depth of 1600 m, deep offshore Niger Delta. The interference test campaign involved 26 pre-first oil wells (13 oil producers and 13 water injectors) to assess and subsequently mitigate reservoir connectivity uncertainties arising from the numerous faults and between the different channels within the complexes. The results proved valuable in confirming or otherwise reservoir connectivity, field oil production rate and the number of wells required at first oil to achieve the production plateau. The tests were designed using the analytical method (PIE software) and the reservoir simulation models enabling to establish the cumulative water injection required, the injection duration and the time a response is expected at the observers. These all had impacts on the planning, OIMR vessel requirements and selection of permanent downhole gauges for the wells. In addition, the tests were performed with the water injectors as pulsers and the oil producers as observers allowing to avoid and the associated environmental impact. Ten interference tests were realized compared to four planned in the FDP partly due to the use of the more cost effective OIMR vessel in addition to the rig.