THE EFFECT OF DENSITY-VELOCITY RELATION PARAMETERS ON DENSITY CURVES IN TAU (τ) FIELD, NIGER DELTA BASIN

Atat, J G,Ekpo, S S,Akankpo, A O,Horsfall, O I,Umoren, E B

doi:10.26480/mjg.02.2020.54.58

Abstract

We considered the constants obtained for tau (𝜏)Field in the Niger Delta basin from well-log data of three wells (A,B,C) to investigate the effect of inclusion of these constants on density-velocity relation using Hampson Russell Software to generate density curve in tau field. The curves were compared to those generated from Gardner and Lindseth constants and in-situ density curves. Many researchers have worked on constants for density-velocity equations for different Fields; their results always differ from Gardner and Lindseth constants including the constants of Atat et al., 2020 which are considered in this investigation as Tau Field local fit constants. Our findings support the results of these researchers. Results indicate over estimation of density curves when using Gardner and Lindseth constants. The challenge is that in-situ density curves are not accurate due to sand-shale overlap of density values. The most improved and accurate result is given by the density curves obtained using the constants for specific sand and shale lithologies (local fits). This verifies the need for the determination of constants for local fit of the oil field under investigation. The pink curves truly indicate the density estimation for the tau field which is very reliable in the characterisation of reservoir.

Highlights

A density-velocity constant depend on geology when result from a good fit using sonic and density well-log information and is very common in the petroleum study (Gardner et al, 1974)
The regression line to make appropriate march with shales and sand with gamma cuff of greater than 75 API for shale was adjusted. This result was considered to obtain different density curves: first, using Gardner and Lindseth default parameters; second, by replacing Gardner and Lindseth constants with the constants of Atat et al, 2020 for specific rock types in the tau field
Density estimated from the well log data is compared to that obtained from local fit constants and Gardner and Lindseth default parameters

Summary

Introduction

A density-velocity constant depend on geology when result from a good fit using sonic and density well-log information and is very common in the petroleum study (Gardner et al, 1974). Gardner’s constants were provided for density-velocity relation to solve the problem of sand-shale overlap. Density is required in the identification of lithologies, pore fluids, porosity and overburden stress estimations and pore pressure prediction; it is one of the major desires in exploration, reservoir characterization and well planning. These constants are nonunique for most datasets from many sedimentary basins across the world as density-velocity data would not obey the original Gardner (Krasovsky, 1981) and Lindseth curves. Overlap in sands and shales could show variation in petrophysical properties (porosity of fluid saturation) making density not a good indicator of lithology (Atat et al, 2020b). Bulk density is an important acoustic indicator of the presence of shale; accuracy in density estimation enables the accurate location of shales in the reservoir

Methods

Discussion

Conclusion