Geosciences-Scholarly Publications

Permanent URI for this collection

https://ir.unilag.edu.ng/handle/123456789/3958

Browse

Browsing Geosciences-Scholarly Publications by Author "Adesanya, O.Y"

Now showing 1 - 3 of 3
  • Item
    Open Access
    Geoelectrical Investigation of Groundwater Potential At Riol Farm, Owode, Abeokuta, Ogun State
    (Journal of the Nigerian Association of Mathematical Physics, 2016) Adeoti, Lukumon; Ijezie, N.T; Adegbola, R.B; Ojo, A.O; Afolabi, S.O; Adesanya, O.Y
    Geoelectrical investigation was carried out in order to solve the problem of drilling unproductive boreholes in RIOL Farm situated at Owode, Abeokuta in Ogun State. Fifteen (15) Schlumberger Vertical Electrical Sounding (VES) with current electrode spacing (AB) ranging from 2 m to 1000 m were acquired using PASI resistivity meter. The VES data were processed and interpreted using partial curve matching and computer iteration technique using WinRESIST software. The qualitative analysis reveals that the rising curves are dry sand devoid of groundwater while the descending parts of the VES curves are indicative of wet sands which could serve as potential aquifer. Four geoelectric sections generated from the interpreted VES results show four to six geo-electrical layers which correspond to topsoil with resistivity ranging between 45.0-993.9 ohm-m and thickness range between 0.5-1.0 m, lateritic clayey sand with resistivity ranging between 61.8-2328.0 ohm-m and thickness range between 1.2-5.5 m, sand/sandstone having resistivity range of between 1003.4-9575.9 ohm-m and thickness range between 4.2-114.8 m, sand with resistivity value ranging from 318.9-1581.2 ohm-m and thickness range between 5.1-78.9 m and consolidated sandstone / ironstone with resistivity value between 23245.5-4388.7 ohm-m. The quantitative analysis reveals that sands at the upper layer are dry within the depth of 2.2 – 69.8 m and appear to be unsaturated while sands at the depth not less than 80 m in VES 2, VES 9 and VES 15 are wet (saturated) and recommended for drilling. Thus, the wet sands denote aquifer units in the study area. Based on our recommendation, the location of VES 15 was drilled and yielded a productive borehole within a depth of 110m.
  • Item
    Open Access
    Lithology and fluid prediction from simultaneous seismic inversion over Sandfish field, Niger Delta, Nigeria
    (Geosciences Journal, 2017) Adeoti, L; Adesanya, O.Y; Oyedele, K.F; Afinotan, I.P; Adekanle, A
    Seismic inversion has been widely practiced in the oil and gas industry because it generates broad bandwidth of impedance data which maximizes vertical resolution and minimizes tuning effects. The lack of accurate prediction of lithology and fluid content of subtle features identified in seismic data acquired over the Sandfish field, Niger Delta, Nigeria necessitated the use of seismic inversion. In this paper, simultaneous seismic inversion is adopted to integrate seismic and well data for quantitative interpretation and uncertainty assessment of the subsurface reservoirs in the Sandfish field. Three Sandfish (Sfn) wells with the required petrophysical logs, check-shot data, high quality 3D seismic data of five angle stacks (6–12°, 12–18°, 18–26°, 26–32°, and 32– 42°) were used for the analysis. A feasibility study including cross-plots of petrophysical and elastic properties from well data was first carried out to establish rock property relationships in the interval of interest. Biot-Gassmann fluid substitution analysis was also used to reveal sensitivity of rock properties to pore-fill type. Low frequency (0–2 Hz) models were generated from interpolation of highcut-filtered P-sonic, S-sonic, and density logs guided by interpreted seismic horizons. The low frequency models were used to broaden the spectrum to estimate elastic volumes. The five partial angle stacks were simultaneously inverted using Jason’s Rock-Trace® inversion software which iterated trial inversions until the model sufficiently matched the seismic data. The inverted P-impedance (ZP), Simpedance (ZS), and density (ρ) were used to derive Poisson’s ratio (σ), volume of sand (Vsand), lambda-rho (λρ), and mu-rho (μρ). The cross-plot of λρ with μρ from well data looks similar to that from inverted results. Sands and shales are discriminated on the basis of sands having low values of μρ. Hydrocarbon-bearing sands are differentiated from water-bearing sands and shales on the basis of having lowest values of λρ. The Biot-Gassmann fluid substitution analysis at reservoir N-01 reveals typical class III amplitude variation with angle (AVA) responses for low-impedance hydrocarbon sands. The lithology and fluid prediction maps extracted from Vsand and σ at the N-01 seismic horizon show variation in lithology and fluid types for the entire volume. The inversion products reveal heterogeneities in the reservoirs away from well control validated by a blind well test. Hence, the study shows that rock-property model from a simultaneous inversion is an effective predictive tool for lithology and fluid types which in turn can guide well placement and predict reservoir development in the field of study.
  • Item
    Open Access
    ON THE EFFECTIVENESS OF USING QUANTITATIVE AVO ANALYSIS IN FLUID AND LITHOLOGY DISCRIMINATION IN AN OFFSHORE NIGER
    (Ife Journal of Science, 2019) Adeoti, L; Ikoro, C.O; Adesanya, O.Y; Ayuk, M.A; Oyeniran, T.A; Allo, O.J
    Quantitative Amplitude Variation with Offset (AVO) analysis of “Jay” Field, offshore Niger Delta, was carried out with a view to properly discriminating fluid and lithology using near, mid and far offset seismic and well data. Seismic and well data were interpreted and analyzed. Synthetic seismogram was generated using density (r) and sonic logs. AVO modeling, seismic AVO attribute analysis and AVO inversion were carried out and the results from well log interpretation using 70-API gamma-ray cut-off, neutron-density over lay and resistivity logs revealed that the field consists of intercalation of sand and shale with typical deltaic depositional environment log signatures. Four identified sand reservoirs (a, b, c and d) with high resistivity values and negative separation in the neutron-density overlay suggested that the field was hydrocarbon bearing probably containing gas or condensate. Two sand reservoirs showed good rock physics results, 'Sand a' at 11,632 ft TVD with 18% porosity (ϕ), 0.25 water saturation (S ), decreasing ratio of compressional wave velocity to shear wave velocity (V /V ) w p Sand Poisson's ratio () relative to the background shale signified AVO response typical of a hydrocarbon bearing sand. 'Sand e' at 5,925 ft TVD, with 30% ϕ, Sw of 1, no change in V /V and relative to the background shale p Simplied that an AVO response was unlikely. Gradient analysis result for the synthetic seismic at the top and base of the two sands agreed with Rutherford's classification scheme for class IV AVO for 'Sand a' and no AVO response for 'Sand e'. AVO attribute analysis and impedance inversion of the seismic volumes confirmed AVO result for the two sands. The study established that AVO technique could be effectively used for fluid and lithology discrimination in the “Jay” Field, Niger Delta.