Focused reservoir characterization: analysis of selected sand units using well log and 3-D seismic data in 'Kukih' field, Onshore Niger Delta, Nigeria

Abstract

This study focuses on the comprehensive reservoir characterization of the 'Kukih' Field within the onshore northeastern Niger Delta region, Nigeria. The absence of its detailed description with delineated reservoir properties, lateral continuity, and their use to identify potential reservoir quality and heterogeneity necessitated this study. Integrating well log and 3D seismic data, the investigation aims to elucidate reservoir properties, lithofacies, and depositional environments to unravel hydrocarbon potential. The geological setting, encompassing the Agbada Formation of Early and Middle Miocene age, is scrutinized through detailed geologic analysis. Petrophysical evaluation of four well logs (Kukih-1, Kukih-2, Kukih-3, and Kukih-4) facilitated the determination of key parameters such as shale volume, effective porosity, and water saturation. Seismic interpretation further enriched the structural characterization of the field. Results showcase three predominant reservoir sands (A, B, and C) with distinct lithofacies and thickness variations. Effective porosity ranges from Fair to Excellent, with permeability exhibiting high values for hydrocarbon reservoir potential. Water saturation trends, lithofacies distributions, and structural features were illuminated through iso-parametric maps and seismic analyses. Depositional environments were inferred through facies analysis, revealing the presence of funnel-, cylinder-, and bell-shaped successions that hint at intricate marine sedimentary processes. Challenges owing to limited core data were acknowledged, and the integration of methodologies emerged as a pivotal strategy for enhanced reservoir understanding. This study underscores the 'Kukih' Field's hydrocarbon potential, accentuating the significance of multidisciplinary approaches in deciphering complex reservoir systems. In light of the petrophysical analysis derived from the well logs and the identification of structural highs through the structural maps, this study recommends the drilling of unexplored zones exhibiting promising structural characteristics.

Keywords: Depositional environment; Facies analysis; Hydrocarbon potential; Multidisciplinary approach; Petrophysical evaluation; Reservoir characterization; Structural analysis.

Figure 1

Showing (a) Kukih Field in relation to the Niger Delta, along the West Coast of Africa, with structures of depobelts, after ^,. (b) Location Map of the Kukih Field with the well locations. Self-developed from well log data with Python [v3.8.8] Programming Language from the Jupyter Notebook [v6.3.0], a web-based, interactive computing platform. (c) Diagrammatic dip profile of the Niger Delta, after .

Figure 2

Methodological flowchart arranged from selected images from subsections of the study.

Figure 3

Workflow output of well-to-seismic tie for Kukih-1, with top horizons of prospect zones (A, B and C), True Vertical Depth TVD (ft), Two-way Time (TWT), Density-Sonic Cross plot, Reflectivity series, Power and Phase spectrum, Seismic traces, Synthetic Seismogram (inserted), Acoustic impedance and Drift (ms).

Figure 4

The Crossplot interface for generating water saturation model.

Figure 5

Identified lithologies (denoted as facies) of mainly sand, shale, and silt intercalations on reservoirs sands A and B across the four wells. It also shows the top and bottom of the reservoir sands marked ‘Sand A’ and ‘A Base’ and ‘Sand B and B Base’ Note: OWC is Oil–Water-Contact.

Figure 6

Distribution of shale across Kukih-1, Kukih-2, and Kukih-3 with lithology from Gamma-ray log. NB: D_VSHL is the Density of shale. GR_VSHL is the shale volume. (GR cut-off = 70 API, Vsh cut-off = 0.35 after ). Kukih-4 is not included due to the unavailability of relevant logs.

Figure 7

(a) Net thickness isopach contour map of Kukih Field (sand A). (b) Net thickness isopach contour map of Kukih Field (sand B). (c) Net thickness isopach contour map of Kukih Field (sand C). Self-developed with Python [v3.8.8] Programming Language from the Jupyter Notebook [v6.3.0].

Figure 8

(a) Average porosity contour map at reservoir sand A (1840 m–1851 m) for the Kukih Field. (b) Average porosity contour map at reservoir sand B (1910 m–1937 m) for the Kukih Field. (c) Average porosity contour map at reservoir sand C (2046 m–2055 m) for the Kukih Field. Self-developed with Python [v3.8.8] Programming Language from the Jupyter Notebook [v6.3.0].

Figure 9

Estimation of Formation Water Resistivity ($R_w$) for Kukih 1–3 using Pickett (linear) plot. Note The red dot on the black line represents the value of $R_w$.

Figure 10

(a) Average water saturation contour map at reservoir sand A (1840 m – 1851 m) for the Kukih Field. (b) Average water saturation contour map at reservoir sand B (1910 m – 1937 m) for the Kukih Field. (c) Average water saturation contour map at reservoir sand C (2046 m – 2055 m) for the Kukih Field. Self-developed with Python [v3.8.8] Programming Language from the Jupyter Notebook [v6.3.0]

Figure 11

(a) Horizon and Fault Interpretation on Inline 1001. A and C are mapped horizons. F2, F3 and F4 are sequential-down-to-basin Growth faults in the time domain, with the direction (N-S) indicated on the location mapped. Dip directions are indicated with white arrows. Sequential-down-to-basin faults are indicated with black arrows. (b) Interpreted horizon interval across Growth Fault on Strike Line (shown as yellow line on location map). F1 and F3 are faults. K2 and K4 are vertical wells. K3 is a deviated well. Sand A and C are mapped horizons.

Figure 12

Synthetic and antithetic faults with inserted well logs from the Kukih field in the depth domain. This diagram was generated using Petrel [v2019.1].

Figure 13

(a) Three dimension time structure map of horizon A. (with wells Kukih-1, Kukih-2, Kukih-3, and Kukih-4 denoted as 01, 02, 03 and 04). (b) Structural top depth map of the velocity model conversion of horizons A and C (with wells Kukih-1, Kukih-2, Kukih-3, and Kukih-4 denoted as Well 1, Well 2, Well 3 and Well 4) It highlights the fault with the dip direction (black arrows) in a 2D section map.

Figure 14

Channelized complex with rollover anticline and the faults acting as hydrocarbon traps. (a) Horizon slice map with channelized sand complex. (b) Seismic section with growth faults (c) Depth map with major faults.

Figure 15

(a, b) effective porosity model (3D and 2D views), (c, d) permeability model (3D and 2D views), (e, f) water saturation model (3D and 2D views generated from the permeability model).

Figure 16

Depositional environment for Sands A, B, and C.