Dorcas Eyinla | University of Ibadan Nigeria (original) (raw)

Papers by Dorcas Eyinla

$Research paper thumbnail of Empirical analysis for the characterization of geo-mechanical strength and pressure regime: Implications on hydraulic fracturing stimulation$

Please cite this article as: D.S. Eyinla, M.A. Oladunjoye, Empirical analysis for the characteriz... more Please cite this article as: D.S. Eyinla, M.A. Oladunjoye, Empirical analysis for the characterization of geo-mechanical strength and pressure regime: Implications on hydraulic fracturing stimulation, Petroleum (2018),

Nine different wells were carefully studied on " PAU " field and their results were integrated fo... more Nine different wells were carefully studied on " PAU " field and their results were integrated for thorough understanding of the reservoir sand bodies within the field. These studies include; stratigraphic well correlation, rock physics analysis, sequence stratigraphy, petrophysical evaluation of wells and reservoir volumetric evaluation in order to understand the prospectivity of the field. Depositional environment and facies change analysis suggest that the field has multiple reservoirs, with shale intercalations. Well logs, Rock physics and sequence stratigraphic methods was employed for reservoir mapping and evaluation of PAU field and The lithologic attributes were integrated with wireline log motifs (gamma ray and resistivity) for paleoenvironmental deductions.

So far, Bulk modulus, Shear modulus, combined modulus of strength and shear modulus to compressib... more So far, Bulk modulus, Shear modulus, combined modulus of strength and shear modulus to compressibility ratio have been actively employed as geo-mechanical parameters that have been used in characterizing subsurface reservoir in Niger delta wells in Nigeria. These can be further utilized to enhance understanding of the pressure in the formation with depth. To successfully maximize hydrocarbon recovery, to minimize sanding rate, and to ensure safety of personnel during and after drilling, pore pressure gradient and its associated fracture pressure has been predicted for each of the abnormally pressured intervals discovered in one of the Niger Delta oil fields by applying Eaton's method. This is aimed at identifying fragile sections. However, empirical relations have been established using geo-mechanical principles. From the two wells studied, geo-mechanical strength increases with depth and tends toward the acceptable range for a competent formation. In the second well, the fracture pressure increases with increasing pore pressure and decreasing Bulk modulus at various depths, while abnormal formation pressure occurred throughout the formation especially at greater depths. The relationship established between geo-mechanical factors and fracture pressure is such that as one decreases, the other increases vice versa.

An integrated approach using, seismic and geological information was employed for the mapping and... more An integrated approach using, seismic and geological information was employed for the mapping and evaluation of the S30, T40, U50 and V60 reservoirs of the Enena field for estimation of the reservoir properties, fluid distribution, and 3D modeling. This research focuses on the integration of petrophysical and structural data to develop an algorithm through Guassian random function simulation for static modeling. The resultant static model was then used for volumetric distribution of the field. The resultant 3D static model shows that S30, T40 and V60 reservoir have a STOOIP of 51.3, 15.1 and 17.1MBO respectively with recoverable reserves of 18, 5.3 and 6 MBO assuming a primary recovery factor of 0.35 and 33.5, 9.8 and 11.1 MBO using a 2P recoverable reserve of 0.65. The GIIP was estimated to be 28, 8 and 9 BCF of gas and the recoverable reserves shows a P1 of 18.2, 5.2 and 5.85 MBO at a recoverable reserve of 0.65 and a 2P of 22.4, 6.4 and 7.2 MBO at a recoverable reserve of 0.8 was estimated. STOOIP and GIIP was not calculated for the U50 reservoir because despite the thick/ good sand package as seen on the GR log, the reservoir was found to be completely water wet. The S30 reservoir is found to be the most prolific both in the oil and gas case. The individual sands and their sub-units are separated by thick to thin shales. It was also estimated that the natural drive mechanism of the Enena field is the water drive and recommended for marginal field operators.

The disposal of waste materials by burial is the oldest form of solid waste disposal. A major con... more The disposal of waste materials by burial is the oldest form of solid waste disposal. A major concern with the usage of traditional dump sites is the potential of polluting groundwater. The pollution could be metals, microbes or other substances. This problem of groundwater contamination from refuse disposal especially those located uphill are worsened when communities that rely on dump site disposal system also depend on private wells for drinking water. Wastewater often makes its way into other water bodies. Water runoff from rain may wash contaminants into the surface waters. A more significant hazard is when pollutants from the drain field move quickly through the soil and potentially into the groundwater making the supposed potable water unusable. The application of methods involving identification of anisotropic behavior and heterogeneities in rocks has become increasingly acceptable because these methods provide adequate knowledge about the presence of fractures and their directions. Observed changes in apparent resistivity with azimuth are typically used for such interpretation which indicates fracture anisotropy. Due to repeated cases of groundwater pollution in the area, this study researches into the application of surface geophysical Original Research Article

Pore pressure evaluation and prediction was undertaken in Malcolm field, offshore Niger Delta, Ni... more Pore pressure evaluation and prediction was undertaken in Malcolm field, offshore Niger Delta, Nigeria using wireline log data. The pore pressure gradient indicator used is the sonic log from three wells namely; A, B and C which were drilled in the field. Ben Eaton's method was used to estimate pore pressure gradient in this research work. Overpressured intervals were also delineated on the sonic log data with the use of a Normal Compaction Trendline (NCT). In well A, normal pressure at depth 6605 ft and 9265 ft with its pore pressure delineated to be 0.449 psi/ft. Abnormal formation pressure at depth 6682 ft, 8914 ft, 9547 ft was delineated to be 0.2686 psi/ft, 0.1250 psi/ft, and 0.1700 psi/ft respectively. In well B, at depths 7573 ft and 9014 ft abnormally low pressure of 0.2942 psi/ft and 0.1159 psi/ft respectively were delineated, while at depth 11106ft, abnormally high pressure was delineated to be 0.6755 psi/ft. In well C, at depths 7447 ft and 8299 ft abnormally high pressure was delineated to be 0.6264 psi/ft and 0.6982 psi/ft respectively, while at depths 9676 ft and 10005 ft, abnormally low pressure were delineated to be 0.1409 psi/ft and 0.2442 psi/ft respectively. There was no normal pressure in well B and C. As a result of these, accurate pore pressures prediction in overpressured regions is essential to ensure safe drilling operations and reduce the cost of drilling.

The epileptic electricity power supply has become a fundamental issue affecting the economic deve... more The epileptic electricity power supply has become a fundamental issue affecting the economic development of Nigeria. Geothermal energy, which results from the radioactive decay of minerals within the Earth's core and solar energy absorbed at the surface, have been discovered and are being utilized by several countries. Nigeria is still far behind in tapping the abundance of geothermal energy resources. Ikogosi warm spring in Southwestern Nigeria is a good geological evidence of potential geothermal energy. Hydrothermal reservoirs can serve as a sustainable potential source of energy because it is renewable. To bring the water or steam from such reservoir to the surface, wells are drilled into them. If the fluid is hot enough, steam bubbles will occur and cause the water to flow naturally to the surface as hot/warm springs, fumaroles and geysers. Ikogosi and other warm springs are visible evidence of geothermal energy in Nigeria. Nigeria may have her energy problem solved if the abundance of geothermal resources, especially one with temperature high enough to generate electricity is utilized. The geological features and subsurface temperature data of oil and shallow water wells from both Northern and Southern part of the Country point to the possible presence of geothermal energy due to the thermal gradient. If tapped, this will serve as alternative energy, as being utilized by several other countries since it can produce base load electricity which is reliable and sustainable unlike many other renewable technologies that are affected by weather and seasonal variations.

Abstract— Recently, the shock hazards that always come along contaminated groundwater in Laka are... more Abstract— Recently, the shock hazards that always come along contaminated groundwater in Laka area of Ogbomoso, south western Nigeria which contain some elements in excess quantity more than the Nigeria standard for drinking water quality 556 (207) recommendation for groundwater potability has become a major concern. With the aim of providing valuable information on hydrogeologic system of the aquifers, subsurface lithology, and delineating groundwater contamination, Thirty three (33) vertical electrical sounding (VES) was carried out utilizing surface Schlumberger electrode arrays and electrode spacing of 50m coupled with hydrogeochemical analysis of the surrounding hand dug wells for Cl-, Ca2+, Mg2+, Fe3+, No3-, calcium, hardness, total hardness e.t.c. The DC resistivity survey revealed significant variation in the subsurface resistivity. Also, VES resistivity curves showed a dominant trend of low resistivity (high conductivity) at shallow depth of ≤15m and later increases with depth. In general the presences of three-four layers were delineated viz.: sandy, sand/gravel topsoil, clay, weathered layer and the fresh bedrock. The thickness and resistivity values range respectively from 0.42 to 2.5m and 13.51 to 150.9Ωm for the top soil, 1.1 to 12.5m and 11.7 to 300.1Ωm for the weathered/clay layer. These anomalous low resistivities indicate area with contaminated groundwater. The result of the hydrochemical analysis also agreed with the presence of contamination.

Abstract: Often, much attention is paid to things that do not majorly “sustain life” while the ma... more Abstract: Often, much attention is paid to things that do not majorly “sustain life” while the main pre requisite to living is usually left unattended to. Geoscience has been a tool used in solving the Earth’s challenges both directly and indirectly. For instance, mining processes as well as hydrocarbon exploration has been aided extensively by the application of Geoscience, whereas Geophysics as a branch of Geoscience, which has proven worthwhile with so much importance in solving societal major need – Agriculture, is not gaining much attention.For agricultural application of geophysical methods, the three of all methods predominantly used are Electrical resistivity, Electromagnetic induction, and Ground Penetrating Radar (GPR). All these three methods are active, requiring artificial application of energy.Electrical resistivity method measures the electrical resistance for a bulk volume of soil which lies beneath the surface. This method basically reveals the subsurface electric field produced by the artificial application of electric current into the ground. An electromagnetic induction method measures the electrical conductivity for a bulk volume of soil directly beneath the surface. An instrument called ground conductivity meter is commonly employed for shallow electromagnetic induction investigations. With the Ground-penetrating radar method, an electromagnetic radio energy pulse is directed into the subsurface, followed by measurement of the elapsed time taken by the radar signal as it travels downward from the transmitting antenna, partially reflects off a buried feature, and eventually when it returns to the surface as it is picked up by a receiver. Past research indicates a wide range of indispensable uses for these three major geophysical methods employed in agriculture. Starting from soil water content monitoring using apparent soil electrical conductivity (ECa) measurements and Soil salinity assessment obtained with electrical resistivity and electromagnetic induction methods, followed by the use of GPR for updating and improving soil survey maps. These are used to evaluate soil property spatial variation.Agricultural geophysical measurements often tend to exhibit substantial variability by measuring soil electrical conductivity, soil dielectric constant (Water Content), spatial, horizontal and vertical changes. The Soil Water Content (SWC) controls important physical, chemical and biological processes such as plant growth, solute transport, rainfall, runoff, erosion, and ultimately pedogenesis. An understanding of the spatial and temporal variability in the soil properties (precision farming) using Geophysical methods will enhance the agricultural produce as well as soil management.Agricultural geophysics is the simplest and the most rapid method of identifying the nature of soil variability in tropical environments as illustrated by some case studies.

Keywords:Agricultural Geophysics, Electrical resistivity, Electromagnetic Induction, GPR, Apparent soil electrical conductivity, Soil spatial property.

Abstract Hydrocarbon exploration and exploitation does not only require the knowledge of hydrocar... more Abstract
Hydrocarbon exploration and exploitation does not only require the knowledge of hydrocarbon in-place,
however, mechanical competency of the reservoir rock must also be known. The direct method of inferring Sand
P-wave velocities from seismic data usually has limitation of poor resolution because of the uncertainty in
seismic inversion which may also affect other derivatives.
An analytical method is presented with the possibility of predicting shear wave velocity from wireline log data
where S-wave sonic logs do not exist. By estimating S-wave velocity, formation geo-mechanical properties can
be calculated using P-wave sonic and density logs with appropriate equations. Elastic constants such as Poisson
Ratio, Young’s, Shear and Bulk moduli which are the parameters for characterizing rock mechanical properties
were estimated and used to predict the mechanical competency of the formation for hydrocarbon exploration.
Well planning demands knowledge of these geo-mechanical properties which can be used to estimate the
pressures required to initiate a fracture into a formation for the safety of the personnel and equipment, in
particular minimizing the associated risks.
In this paper, firstly we investigate the possibility to predict the shear velocity from well logs, and then Elastic
moduli calculated from the log data can therefore be used effectively in predicting safety limits in sand-free
production from friable sandstones.
The results of this study shows that the combined modulus of strength (K) and the shear modulus (S) to
compressibility (c) ratio (S/c) for the formation are relatively low. The average value of K is lower than the
threshold value indicating the minimum value at which fluids may be produced safely at any rate but falls within
the range which generally represents a condition in which the problem of sand production should not arise below
a certain optimum flow rate. Average value of S/c ratio is lower but tends towards acceptable range.

Keywords: Mechanical competency, predicting shear wave velocity, elastic constants, well planning, combined
modulus of strength, shear modulus to compressibility ratio.

$Research paper thumbnail of Empirical analysis for the characterization of geo-mechanical strength and pressure regime: Implications on hydraulic fracturing stimulation$

Keywords:Agricultural Geophysics, Electrical resistivity, Electromagnetic Induction, GPR, Apparent soil electrical conductivity, Soil spatial property.

Keywords: Mechanical competency, predicting shear wave velocity, elastic constants, well planning, combined
modulus of strength, shear modulus to compressibility ratio.