Reservoir characterization and volumetric estimation of reservoir fluids using simulation and analytical methods: a case study of the coastal swamp depobelt, Niger Delta Basin, Nigeria

Abstract

Suites of wireline well logs and three-dimensional (3D) seismic data were integrated to characterise the reservoir and estimate the hydrocarbon in Otigwe field, coastal swamp depositional belt, Niger Delta. The 3D seismic data were used to generate seismic sections through which fourteen faults and two horizons of interest were mapped across four wells. Depth structural map generated from the mapped faults and horizons of interest shows that the trapping mechanism within the field is fault-supported anticlinal structural trap. The four available wells were correlated using lithostratigraphic correlation to establish two reservoir continuities (Reservoir A and B). The estimated reservoir fluid volume at surface condition using reservoir simulation and modelling software is 59 MMstb for reservoir A and 25.70 MMstb for reservoir B. On the other hand, the estimated reservoir fluid volume at surface condition using analytical method is 52.58 MMstb for reservoir A and 18.85 MMstb for reservoir B. Using reservoir simulation and modelling software, the average net-to-gross ratio and shale volume for reservoir A range from 0.86 to 0.89 and 0.11 to 0.14, respectively, while for reservoir B the range is between 0.69 to 0.82 and 0.18 to 0.31, respectively. On the flipside using the analytical method, the average net-to-gross ratio and shale volume for reservoir A is 0.78 and 0.22, respectively. The results from the volumetric estimation of reservoir fluids showed close values using both methods and reservoir A is more prolific compare to B.

Reservoir Static Modelling towards Safe CO2 Storage in Depleted Oil Reservoirs of ‘CRK’ Field, Niger Delta, Nigeria

“…1 describes the approximate location of the study area; its actual name and further details about its location were withheld due to certain confidentiality agreement. The Niger Delta, situated in the Gulf of Guinea along the West Africa Margin, lies between longitude 5 °E to 8 °E and latitude 4 °N to 6 °N [16]. It is deemed one of the most prolific deltaic provinces in the world in terms of hydrocarbon accumulation and has a clastic wedge sedimentary thickness of up to 12km [22].…”

“…A combination of the wireline logs such as the gamma ray, sonic, density and resistivity logs were used for the lithology discrimination and in estimating the reservoir properties. Petrophysical properties such as porosity (ϕ), Permeability (K), water saturation (Sw), Volume of Shale (VSH), Net-to-Gross (N/G), reservoir thicknesses and caprock thicknesses were estimated from the available wireline logs following the methodology and standard formulae documented in [13,16,18].…”

“…For instance, the total porosity (𝜙) was estimated using Tixier formula with density log being the key input [16,18];…”

“…In order to access a good fit for resource estimation, optimize production efficiency, enhance cost-effectiveness and economic feasibility of subsurface resources, the technique of 3D modelling of rock properties and fluid characteristics has been adopted and used for decades [13,14,15]. This involves incorporating seismic data, core samples, well logs and other geological information to create a comprehensive representation of rock properties in threedimensional space [16]. In its very adequacy, 3D modelling allows for revealing the distribution of reservoir properties even in multiplex reservoirs with lateral and vertical lithologic variations, leading to enhanced volumetric estimation, risk and uncertainty analysis, predictions of fluid flow and field development plans.…”

“…Although there has been several 3D static modelling attempt at some reservoir units of the Niger Delta basin, notably the works of Adeoti et al [13], Hammed et al [17] and Kura et al [16], all of which were targeted mainly at hydrocarbon prospectivity and reserves estimation without commenting on the implications for carbon sequestration. Also, recent studies on carbon capture and storage in the region have focused primarily on general review of the technology [5,7], capacity estimations [18,19] and assessment of the structural and stratigraphic competence of some reservoir units of the basin [20,21].…”