Effect of hydrocarbon gas on the seismic frequency attributes was studied and considered for applicability as Direct Hydrocarbon indicator (DHI) in the AN reservoir in the Niger Delta basin. Matching Pursuit algorithm for the spectral decomposition was adopted for frequency attributes analysis at 10Hz to 35Hz, along the interpreted reservoir top. Three frequency surface attributes were co-rendering and color blending to highlight the effect of gas in the reservoir. Gas filled sand exhibits distinctly higher frequency amplitudes at low frequency bands of 15Hz to 25Hz despite a subtle hardness of the sand relative to the overburden thick shale. High frequency amplitude expression in the low frequency (15Hz-25Hz) band observed in the gas reservoir is found to be a consistent character of overpressured gas reservoirs within the Niger Delta basin. It was concluded, therefore based on time-frequency seismic character of the gas sand, that frequency attribute can be used as a direct hydrocarbon indicator for the sandstone gas reservoir in the Niger Delta.

The presence of oil rim in gas reservoirs could potentially have an impact on the timing and philosophy of gas development in the field. Sound reservoir management strategy requires investigation of the development feasibility of the oil rim as part of the field development planning study. This is also a prerequisite to securing regulatory approval for the resulting field development plan. Eleju C1000 reservoir contains a proven 10ft oil rim with a huge gascap supported by clearly logged fluid contacts. The field is located onshore Niger Delta, with six well penetrations, leading to the discovery of nine hydrocarbon-bearing sands. The field development concept is based on the gas resource in C1000 reservoir, which holds over 80% of the estimated field gas in-place volume. Based on the available geoscience and engineering data, analytical and simulation methods were employed to evaluate the feasibility of developing the 10ft oil rim in C1000 reservoir. The operator's Oil Rim Development Guidelines and Wyne et al Matrix (for evaluating oil reservoir feasible concept) were employed in selecting an optimum development concept for the C1000 reservoir. Analytical and simulation methods resulted in C1000 estimated EUR per well range of 0.3 – 0.4 MMstb with a unit development cost (UDC) of about $100/bbl excluding flowlines and facility. This is not economically favourable to the project which has a UDC of $3.4 per boe for gas development only. Therefore, the optimum development option for reservoir C1000 is gas development only.

Multirate welltests are conducted to determine well deliverability, skin and distance to major fault boundary; as well as reservoir data like permeability and pressure. A reservoir was planned for development with four wells to supply about 500 MMscf/d of gas to a primary treatment facility. The proposed wells were designed for multirate welltests to boost confidence on meeting the gas supply obligation. The multirate welltest program includes (1) Initial Build Up, (2) Flowing, (3) Final Build Up and (4) Static Survey periods. The test design determines optimal duration for each activity in the program; to ensure the test objectives are achieved. This paper shares results of the test designs for the wells and insights gained from the exercise. The results show that wells close to boundary fault (less than 250 m gap) were not good candidates for final build up survey as the fault signal appears early (within 0.1 hr survey time) as boundary effect; thereby overlapping with wellbore storage effect phase and masking infinite acting radial flow period (used for estimating well and reservoir parameters). Hence, final build up was not proposed in such wells. Those parameters can be estimated from other wells in the same reservoir. Sensitivities were done by varying the reservoir structure, permeability, well skin and wellbore storage effect. Test design results also show that infinite acting radial flow period signal was observed within 0.1 to 2 hrs of final build up; followed by fault boundary response visible from 2 to 24 hrs. It can be concluded that final build up survey period of 10 hours is optimal to meet the test objectives.

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The management of uncertainties associated with ‘green fields' remains a challenge due to data paucity. In the context of rising development costs for oil and gas projects, integration of data from all available sources becomes imperative. This integration has been demonstrated to reduce identified subsurface uncertainties and risks. Biostratigraphic data which comprises use of forams and fauna from ditch cuttings picked in several reservoirs in the field has been evaluated and is used to delineate the sequence stratigraphic boundaries which have been shown to be useful for building the framework for field correlation, thus the building of realistic static models. The CAMOY Gas field located onshore Niger Delta basin was discovered in 1961 by CAMO-1 well. To date, a total of six wells have been drilled in the field. The field is split into two fault blocks by CAMO fault (an East-west trending fault) in the south. The minor block is penetrated by just one well, with the remaining five wells in the main block. A total of nine hydrocarbon-bearing reservoirs have been penetrated occurring between the depths of 6500 ftss and 11000 ftss. Key subsurface uncertainties that impact on the development plan of the B4 gas reservoir have been identified, and they are associated with structure and stratigraphy. A range of static volumes were computed initially based on the original understanding of the underlying structural and stratigraphic uncertainties. However, by integrating biostratigraphic data in the reservoir correlation, the uncertainty associated with stratigraphy is reduced, leading to a more realistic range of volumes. Following the building of a realistic 3D model and volume ranges, two wells have been proposed to be drilled to develop the reservoir. The placement of one of the wells closer to the CAMO fault has been optimized post application of biostratigraphic data in B4 gas reservoir correlation.