Overpressure Prediction In The North-West Niger Delta, Using Porosity Data (original) (raw)
Related papers
Porosity as an overpressure zone indicator in an X-field of TheNiger Delta Basin, Nigeria
Archives of Applied Science Research, 2011
Over the past decades, overpressure zones have been routinely identified in the Niger Delta by means of resistivity logs, dc component logs, direct measurements (using pressure level detectors attached to BHA) and penetration rate of the drilling bit. The present research, however, applies porosity as an alternative method for overpressure zone detection. The application of porosity as a tool for overpressure detection is demonstrated using plots of porosity versus depth for two wells in an X-field in the Niger Delta. Results show that between 5000ft and 7000ft depth, (for well-1) there is continuous decrease of porosity values with depth. At 7000ft, however, there is an abrupt shift to the right side of the plot, indicating abnormally high porosities (at least for the delta), with values ranging from 25% to 35%. Such abnormally high porosities suggest that the pore fluids support a disproportionately large part of the overburden (from the Benin Formation mainly), leading to an over...
International Journal of Advanced Geosciences
The Depth-dependent compaction theory that variations in certain geophysical properties with depth; bulk density, formation resistivity together with sonic velocity being a reflection of the pressure regime is the basis for pore pressure prognosis study. Pore pressure prediction (PPP), when done accurately can be used to avert disaster and helps in safe drilling. A porosity-based model has been applied to predict overpressured zones in an onshore environment of the Niger delta basin. Zones with hard overpressures greater than a magnitude of 0.7 psi/ft are generally within 10000ft and below. Top of overpressures for studied wells ranges between 7000ft and 10000ft. Porosities in shale are of typical values ranging between 0.05 to 0.46. A robust concordance between PPP and MPP profiles for each of the wells validates the results here and confirms suitability of model to the studied area.
International Journal of Advanced Geosciences
Prediction and evaluation of overburden pressure are critical for the exploration and production of hydrocarbon reservoirs. Overburden pressure was estimated using well log (density and sonic) data obtained from two wells (B1 and B2) of an X - Field within the Niger Delta basin. Overburden pressure depends primarily on the bulk density data. Bulk density was extracted from density and sonic logs based on the log signatures. The bulk density was then used to determine overburden pressure using Eaton’s equation. The results reveal that overburden pressure increases linearly with depth, and an overburden gradient of 1.0 psi/Ft. was obtained. The overburden pressure was used to estimate pore pressure and vertical effective stress and thus enabled the determination of overpressure zones within the well.
International Research Journal of Advanced Engineering and Science, 2021
This research was carried out in the Agbada Field in the Central Swamp area of the Niger Delta Petroleum basin. Well-log and seismic data were used to predict pre-drill pore pressure in the subsurface rock matrix. Variables estimated from the offset well included overburden gradient, shale pore pressure and fracture gradient. While those estimated from the seismic data included seismic velocities, pore pressure and fracture gradient. Mild overpressures were encountered in the calibration well from 10,800ftss to 11,702ftss where pressures of between 0.5 and 0.51 psi were observed. Hard overpressures of between 0.77 and 0.81psi were also seen from 13,318ftss to the bottom of the well at 14,502ftss. Vertical effective stress reversal which is also an indicator of overpressure was observed at 11,702ftss. Another indicator of overpressure, overburden pressure, increased from 11,800ftss as well, and a corresponding fracture gradient also increased at 14000ftss. While the total drilled depth of the calibration well was 14,508ftss, the total sampled depth of the seismic velocities was more than 18000ftss (about 5000ms). The seismic derived fracture gradient increased between 2800ms and 3000ms (about 13,800ftss) in agreement with that calculated from the calibration well. Vertical effective stress reversal was also observed between 2500ms and 3,500ms (10,000ftss-14,000ftss), just as was observed in the well. Overburden pressure dropped between 2800ms and 3000ms. This was also confirmed from the well results. Mild overpressures were predicted from 2500ms to 2650ms (10,00ftss to 10,700ftss) and hard overpressure from 2700ms to 3100ms (11,000ftss to 13,200ftss). Seismic velocity and well-log data were in good agreement for the pore pressure profile of the calibration well.
2015
Proper detection and prediction of overpressure zones is one of the biggest challenges facing the oil industry in particular as exploration moves into deep water environs. The origin of overpressure and its effects on the petroleum systems are complex, difficult to quantify and may result in kicks and/or blow-outs if not adequately detected, predicted and accounted for before and during drilling. The main thrust of this paper is overpressure detection using well log and check-shot data from three wells drilled onshore Niger Delta which were sourced from the Department of Petroleum Resources. These data sets were interpreted qualitatively using RokDoc (powered by Ikon Science) and Microsoft Excel software for the purpose of overpressure detection, correlation and normal compaction trend (NCT) analyses. The results revealed five possible continuous overpressure zones intercalated within probable hydrocarbon bearing reservoirs between a depth of 6,147.50 ft (1,873.76 m) and 9,998.66 ft...
Detection and estimation of overpressure using borehole data
Detection and estimation of overpressure using well data have been attempted. Suites of logs from three wells in the overpressured oil fields of the Niger Delta were used. Using the formation pressure information, the hydrostatic pressures of the three wells were derived. Working intervals were carefully selected from the same lithology (shale) within the depth of interest (6,000ft-15,000ft) using gamma ray log. Overpressured formations display numerous properties when compared with a normally pressured zone at the same depth. The crossplots revealed the behavior of these properties with increasing depth. Comparison of these rock properties at different depth points showed changes in their trend behavior. Overpressure zones were significant with increasing depth (9,000ft).
Pore Pressure Prediction in Offshore Niger Delta: Implications on Drilling and Reservoir Quality
Despite exploration and production success in Niger Delta, several failed wells have been encountered due to overpressures. Hence, it is very essential to understand the spatial distribution of pore pressure and the generating mechanism in order to mitigate the pitfalls that might arise during drilling. This research provides estimates of pore pressure along three offshore wells using the Eaton's transit time method. An accurate normal compaction trend was estimated using the Eaton's exponent (m=3). Our results show that there are three pressure magnitude regimes: normal pressure zone (hydrostatic pressure), Transition pressure zone (slightly above hydrostatic pressure), and over pressured zone (significantly above hydrostatic pressure). The top of the geopressured zone (2873 mbRT or 9425.853 ft) averagely marks the onset of overpressurization with the excess pore pressure ratios above hydrostatic pressure varying averagely along the three wells between P * = 1.06-24.75 MPa and the lithostatic load range is λ = 0.46-0.97 and λ * = 0.2-0.9. The parametric study shows that the value of Eaton's exponent (m = 3-6) need to be applied with caution based on the dominant pore pressure generating mechanism in the Niger Delta. The generating mechanisms responsible for high pore pressure in the Offshore Niger Delta are disequilibrium compaction, unloading (fluid expansion) and shale diagenesis.
Springer, 2021
Few wells targeting high temperature, high pressure intervals in most tertiary sedimentary basins have achieved their objective in terms of technicalities and cost. Since most shallow targets have been drilled, exploration focus is drifting into deeper plays both onshore and in deep offshore areas. To ensure safe and economic drilling campaigns, pore pressure prediction methodologies used in the region needs to be improved. The research aims at generating and testing a modification of Eaton's equation fit for high temperature, high pressure intervals on a field. The evolution of pore pressure in the field was established from offset well data by making several crossplots, and fracture gradient was computed using Mathew and Kelly's equation. Eaton's equation parameters were then calibrated using several wells until a desired field scale result was achieved when compared with information from already drilled intervals i.e., kicks and RFT data. Seismic velocity data resulting from high density, high resolution velocity analysis done to target deep overpressured intervals were then used to predict 1D pore pressure models at six selected prospect locations. Analyses reveal depths shallower than 3800 m TVD/MSL with geothermal gradient 3.0 °C/100 m and pressure gradient less than 1.50sg EMW are affected mainly by undercompaction; depths greater than 3800 m TVD/MSL with geothermal gradient of 4.1 °C/10 m and pressure gradients reaching 1.82-2.12sg EMW are affected by unloading with a narrow drilling margin for the deep highly pressured prospect intervals. Eaton's n-exponent was modified to 6, and it proved accurate in predicting high overpressure in the first prospect wells drilled.
Journal of environment and earth science, 2016
Overpressure in the world’s sedimentary basins are known to be allied with permeability barriers, tectonics, shale digenesis, basin structure and undercompaction factors. The Niger Delta basin has many overpressured zones with different depositional enviroments. This study was done using six drilled wells log suits in an x- field (Gama ray log, deep induction log, Density log, and sonic log). The data was acquired from Cheveron Nigeria Ltd in ascii softcopy format, which was analysed using both manual method and computer processed interactive petrophysics (IP) version 3.6 software. The logs were loaded and printed to hardcopies and digitization done at 5m interval to extract the data across the log suits. Characteristic curve patterns along the gamma log were delineated for shape patterns such as bell shape, funnel shape, and blocky to reveal paleoenviroments of the study area. The results indicate twenty one (21) overpressure zones within the wells, three (3) subsurface overpressur...