Document Type : Research Article
Authors
1
1- Department of Petroleum and Mining Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran. 2- National Iranian Oil Company, Exploration Directorate (NIOC-EXP), Tehran, Iran.
2
Geoscience Faculty, Research Institute of Petroleum Industry (RIPI), Tehran, Iran
3
Department of Petroleum and Mining Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran
4
National Iranian Oil Company, Exploration Directorate (NIOC-EXP), Tehran, Iran
5
Earth Sciences Department, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran
10.22034/anm.2024.19796.1590
Abstract
An authentic understanding of formation pore and fracture pressures is essential to define a safe and optimum mud window in drilling oil and gas wells. This investigation is a challenge in formation pressure studies in the South Azadegan field, which is typically carbonated with very low traces of shale beds, except in the Kazhdumi Formation. The wells drilled in this field hinged on the geological information and pore pressure alterations, can be categorized into three classes; Gachsaran, Pabdeh, and surface formations containing marl. These parameters directly affect the selection of the casing shoe depth and the well schematic. Correspondingly, target reservoir formations, i.e., Sarvak, Kazhdumi, Gadvan, and Fahliyan, and well profiles are other parameters that can classify wells in terms of drilling. It is necessary to analyze and model all upper formation pressures to obtain more precise results to investigate the pore pressure profile in these formations. Effective pressure log data reveals an increasing trend in formation pressure with depth in all wells. Besides, there are a few effective pressure-velocity data pairs in the total data of the Fahliyan Formation of Azadegan wells. With the small number of effective pressure-velocity data pairs in the total data of the Fahliyan Formations of Azadegan wells and the very low correlation coefficient of the Bowers relation for the wells of the Fahliyan Formations, it was necessary to separate this formation into two upper and lower parts. So the modeling has been performed by constructing compressional velocity-effective pressure cubes. This research was based on the data gathered from various drilled wells in this region and the interpretation of seismic data. Also, the effective, pore and formation fracture models have been determined from the integrated geostatistical models validated with the pressure-volume fractal model. The most heightened correlation between the final velocity and effective pressure cubes corresponds to the Ilam with 0.71 and the lower Fahliyan Formations with 0.86, which signifies the model's accuracy with the original data. Based on the final pressure cubes of the formation, the maximum pore pressure of 10,000 psi in the Gadvan to Upper Fahliyan Formations and the maximum fracture pressure of 13,000 psi in the lower Fahliyan to Gotnia Formations have been obtained. In this research, an innovation has been made to study the formation pressures utilizing fractal pressure-volume (P-V) methods. Also, for the construction of the final formation pressure cube model in the entire area of the South Azadegan field, for the first time, the combination of geostatistical methods of sequential Gaussian simulation (SGS) and co-kriging with the acoustic impedance (AI) cube obtained from seismic inversion has been used together. Computation of the Logratio matrix resulting from the fractal pressure-volume model revealed the maximum overall accuracy (OA) in the dominant limestone intervals as 0.74 at the depths of 2000-3000 meters, corresponding to the Sarvak to Asmari Formations. The results exhibit the high correspondence of the pore pressure cube model, obtained by sequential Gaussian simulation (SGS) combined with co-kriging and acoustic impedance inversion.
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