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.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWith 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 wireline 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.