Detection and estimation of overpressure using borehole data (original) (raw)
Related papers
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...
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.
Overpressure Prediction In The North-West Niger Delta, Using Porosity Data
Overpressure prediction in the North West of Niger Delta, using porosity data was carried out to safeguard hazards associated with drilling accident due to blowout. In the absence of seismic data to predict overpressure, porosity-dependent parameters and acoustic impedance could be used to predict the tops of overpressured zones in the area of study in the Niger Delta. Overpressure prediction is vital for safe and economic drilling. Composite logs were used to obtain the required data by digitizing the logs and deduction using the appropriate relationships. The findings from the study show that porosity decreases with depth, with overpressure zone detected at about 3500m depth due to porosity deviation from normal trend. Pressure gradient in the upper normal pressure of the field is determined to be 0.989 psi/ft, this implies that within the established normal pressure gradient of 0.71 -1.1 psi/ft in the Niger Delta. Formation overpressure gradient is determined to be 1.40 psi/ft. The overpressure zone coincides within the high shale-to-sand ratio of Agbada under compacted Formation. The identification of the tops of overpressure zones in any formation penetrated by a borehole enhances the use of normal drilling techniques of the borehole. This also reduces the cost of drilling the entire well as the special drilling technique will be applied only in the overpressure zones. This finding can aid in the prevention of drilling accident and resource wastage in exploration activities.
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...
Detection of Overpressure using 3D Seismic Response in the AL Field in the Niger Delta, Nigeria
Three dimensional (3D) seismic and well-log data acquired in AL Field in the Niger Delta is analyzed to predict overpressured zones ahead of drilling using RocDok, VITAL and Excel softwares. The pressure increases to 0.67psi/ftah at a depth of about 12400ftah. At a depth of about 12600ftah, the pressure stabilizes and then gradually increases to 0.8psi/ft at a depth of about 15200ftah. From depth estimations, the three target reservoir levels are at depths of 11500ftss, 11700ftss and12400ftss. The implication is that the reservoirs experience hydrostatic to mild overpressures. The onset of mild overpressure has been interpreted at 11.5MFS corresponding to a depth of 11,500ft true vertical depth. The onset of hard overpressure has been interpreted at 12.1MFS corresponding to a depth of 12535ft. Using seismic method, overpressure is detected at 12400ft having pressure gradient of 0.67psi/ft.The results of this work can be used to predict overpressured depths and drilling rig capacity ahead of drilling in the area of study.
Journal of Petroleum Exploration and Production Technology
One of the complexities of geomechanical study is in the classification of rock’s properties and overpressured intervals—a knowledge which is not only essential for well safety and cost-effective drilling, but crucial in evaluating exploration risk factors and ensuring a successful hydraulic fracturing program. In this study, a more robust prediction of reservoir pressure regime is presented, where the geomechanical distributions of the rock give a distinct correlation. Three wells from the Niger Delta Basin were studied using empirical equations to estimate the elastic properties, wave velocities and the rock physics parameters for each well. From the results obtained, the velocities of compressional wave (Vp) and shear wave (Vs) decrease as porosity increases. Also, a linear correlation exists between Poisson’s ratio and Vp/Vs, where both variables showed distinct behavior and similar trend serving as useful tools for lithology identification. Another significant observation is th...
Detecting and Predicting Over Pressure Zones in the Niger Delta, Nigeria: A Case Study of Afam Field
Journal of Environment and Earth Science, 2014
An investigation of the overpressure condition in Afam field was carried out using a suite of borehole logs and 3D seismic data obtained from Shell petroleum Development Company of Nigeria (SPDC) with a view to detecting and predicting abnormal pressure zones in the area. The methodology employed knowledge of well lithology and more detailed information extracted from inverted seismic traces. The interval velocity data of some shot lines within the study field and its immediate environment were computed to ascertain the pressure variations and the geological model of the less known areas from seismic data. Using well data near the seismic trace for calibration, precise stratigraphic interpretation of the constructed interval velocity section was carried out. The overpressure zones were identified and probable hydrocarbon distribution pattern within the field was established and correlated with the geology of the study area.. The results obtained revealed five tops of overpressure (TOV) namely TOV 1, TOV 2, TOV 3, TOV 4, and TOV 5 at 1608.8m, 1884.1m, 2387.3m, 2708.9m and 3001.4m respectively derived from seismic and lithologic logs including their lateral variations. .The plot of the Normal Compaction Trend versus velocities obtained from sonic logs also confirmed the identified overpressure zones. The five horizons representing the identified overpressure zones were picked on the 3D seismic sections at 1.42 s, 1.75 s, 2.01 s, 2.11 s and 2.30 s respectively, with thickness varying from 4.08 m to 50.58 m. In-addition, the water saturation (Sw) and porosity () φ values calculated showed that the overpressure zones were generally characterized by high water saturation (52 % to 80.36%) and low porosity (16.55 % to 30.80 %). Furthermore, four hydrocarbon-bearing zones, which were overlain by thin over pressured shale beds, were delineated at 2657 m, 2804 m, 2916.9 m and 3048 m respectively. This case study shows how knowledge of well site lithology and detailed information from seismic data could enable prediction match well conditions with high fidelity thereby reducing drilling cost, prospect risk and improving safety..
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...