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Three dimensional static reservoir modeling is a key aspect of geoscience workflows underpinning development of petroleum reservoirs. It helps accurately characterize reservoirs, plan appraisal and development wells, and achieve high-level Well and Reservoir Management (WRM) over the production life. Facies modeling is a critical step in the static modeling workflow because it allows us model how rock types are distributed in the reservoir and whichis the basis for modeling petrophysical property ranges associated with each facies type. The object-based approach to facies modeling has been well established within the oil and gas industry over the last ten years, however, recent efforts have been made to model reservoir facies using neural networks. This paper reports on the application of the neural network approach to facies modeling as part of the static modeling workflow for several turbidite reservoirs in an offshore Nigeria oil field. The key input data applied to delineate and model the facies were cores, well logs, and seismic. The authors consider this modeling approach to be successful and recommend it for modeling deep water facies with better thin-bed placement, high repeatability, and a shorter turn-around time.

The azimuthal density while drilling tool has been successfully utilized in high angle well drilling and evaluation. The evolution of the imaging technology from this tool has opened new avenues in horizontal well evaluation, and the resultant imaging answer product has successfully been used for detailed structural and sedimentological analysis for characterizing reservoirs beyond the resolution of surface seismic. Conventional well to well correlation techniques have often proven inconclusive in placing laterals in the optimum position within the reservoir. Resulting production from the lateral drain holes has been seen to be greatly influenced by the positioning of the well bore relative to structural and formation dip. Formation dip and structural features have historically been acquired from wire-line logging tools. However, high angle wells present operational difficulties which often result in a decreased use of wireline. Images acquired while drilling by the azimuthal density tool provide a method of resolving the correlation uncertainties, and allow quantification of the structural and sedimentological interpretation and the subsequent production contribution of each zone in the lateral. The fields where this application was utilized are analyzed. From the data analysis an extra opportunity in terms of reserves has been identified. Introduction The results have shown the utility of the azimuthal density tool in producing images that have defined well placement relative to reservoir geometry. The data has also been used in dip computation for re-interpretation of the seismic cross section top structure maps. These results have also assisted in resolving flow profiles, reservoir contributory factors, and have been used to steer the well geologically allowing optimal lateral placement. These applications have been utilized by Shell in Nigeria for horizontal well evaluation. A case study of two horizontal wells is presented in this paper which illustrates the application of azimuthal density images in structural dip computations, facies and depositional environment classification, and for sand count computation used to accurately estimate the Net/Gross ratio. This application has identified opportunities in some old fields, which has resulted in the booking of extra reserves. Recommendation is made that the production philosophy of all horizontal wells be reviewed to identify similar gains. Theory The azimuthal density tool (Figure1) measures neutron porosity, photo electric effect, ultrasonic caliper, and bulk density. The VISION475* system combines surveying with full formation evaluation in slim holes. The PowerPulse* MWD or IMPulse* tools telemetry system can be programmed with a variable list which permit the Up and Bottom quadrant density measurements to be transmitted in real-time for geosteering applications and for accurate reservoir placement. The apparent dip can also be predicted with these two measurements at the wellsite in real-time. When the lateral is placed along the dipline or when the borehole is near parallel to the bedding plane, this will indicate whether the borehole is moving updip or downdip and the apparent dips. Primarily, density contrast is what is required in order to identify a bedding plane.

With the introduction of azimuthal density while drilling tool into the stream of LWD technology in the last decade, a new frontier in understanding and evaluating lateral composition and architectural variability in most reservoirs has been made possible, by the utilisation of this tool in the drilling of high angle wells in the Niger delta. The availability of imaging technology from this tool and the resultant imaging answer product has been used for detailed structural and sedimentological analysis in characterizing reservoirs beyond the resolution of surface seismic. Determination of reservoir properties based on genetic units and identification of flow zones that could potentially contribute to production were derived to enhance the reservoir models for such reservoirs and improve reservoir management. In most cases, the optimal placement of high angle wells using the conventional well to well correlation techniques have often proved unreliable, due to unexpected lateral discontinuity in the reservoir quality. These occurrence in many reservoirs have been associated with varying sedimentary structures, micro-faulting and unexpected changes in environment of deposition, as evident in Niger delta depobelts. Resulting production from high angle drain holes has been seen to be greatly influenced by the positioning of the well bore relative to structural and formation dip, apart from other completion related problems. Formation dip and structural features have historically been acquired from wire-line logging tools. However, electric logging in high angle wells presents operational difficulties which does not encourage the use of wireline logging.. Images acquired while drilling by the azimuthal density tool provide a method of resolving the correlation uncertainties, and allow quantification of the structural and sedimentological interpretation and the subsequent production pattern across the lateral wellbores. Two field examples where azimuthal density data were acquired and utilized are analyzed. From the data analysis an extra opportunity in terms of reserves were identified. Introduction Drilling of horizontal wells has progressed significantly in the past seven years in Shell Nigeria, after the first horizontal well, Sapele 24, was drilled in 1992(1). The concept of drilling pilot holes before the objective horizontal targets have reduced with increasing learning curves associated with understanding of horizontal drilling techniques, proper placement of wells across the objective sands and the use of efficient completion methods. However, shortfall in the actual production performance of most of the horizontal wells against planned had resulted in a comprehensive review of horizontal well's performance(1), including having adequate data in the wells to understand lateral geological properties and the flow behaviour across the well bores. In most of the horizontal wells, GR and resistivitity were acquired using LWD or during wash down trips. However, logging of azimuthal density tools, ADN or equivalent tools was not considered critical then, since most of objective reservoirs were assumed to be homogenous, mainly channel/shoreface deposits. While this may be true in some cases, most reservoirs have shown the tendency for facies variations and quite some geological surprises have been observed. Understanding the environment of deposition in all the axes of the Niger delta depobelt has therefore necessisated the acquisition of porosity data to improve on horizontal well evaluation, thereby explaining the production behavior in such wells. In addition, remedial activities and long term oil recovery in these reservoirs could be addressed using such adequate data.