Pore Pressure Prediction Methods
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A predrill estimate of formation pore pressure is a key requirement for successful exploration and drilling. During the exploration phase, knowledge of the spatial distribution of formation pressures can be used to develop fluid migration models, to study the effectiveness of seals, and to rank prospects. During the drilling phase, a pre-drill pore pressure estimate allows the appropriate mud weight to be selected and the casing program to be optimized, thus enabling safe and economic drilling. This course will cover the fundamental principles of pore pressure modeling and application to oil field problems. The basic concepts used in pore pressure prediction will be presented, and methods for estimating pore pressure using log and seismic data will be explained and discussed. The discussion will focus on deriving a calibrated pore pressure model from seismic velocities. This implies calibration with offset well data in order to derive a calibrated velocity-to-pore pressure transform. The different data types used for optimal model calibration will be presented. The rock physics basis underlying such transforms is discussed, and their application to pore pressure modelling is illustrated using several examples from the Gulf of Mexico. By understanding how the pre-drill pore pressure model is built, and what kind of calibration data is necessary, the course participant will get a sense of how to update and re-calibrate the model in real time while drilling. The following topics will be addressed: Processes responsible for abnormal pressure, Methods of pore pressure prediction and detection, Data requirements and how to deal with data gaps, Model calibration, Advantages and disadvantages of seismic and resistivity based pore pressure prediction, Real time updating and uncertainty analysis.
Introduction. Geological occurrence and processes responsible for abnormal pressure (disequilibrium compaction, fluid expansion, smectite/illlite transformation, hydrocarbon generation). Definitions and importance of pore pressure in exploration and drilling. Drilling problems related to pore pressure. State of stess in the Earth - fundamentals, measurements and modeling. The concept of effective stress. Pore pressure prediction and detection. Seismic-based methods. Resistivity-based methods. Basin modeling approach. Evaluation of the different methods.
Data audit, data requirements and how to deal with data gaps. Overview of data types necessary for real time monitoring and model updating. Estimation of stresses: Density and the calculation of vertical stress. Practical exercise on vertical stress determination. Pore Pressure and Fracture Gradient - modelling and prediction. Loading and Unloading and how it relates to different pore pressure mechanisms.. Fracture gradient, formation integrity and leak-off tests for calibration of minimum horizontal stress.. Relation between pore pressure and fracture gradient. Practical exercise on determination of minimum horizontal stress. Influence of pore pressure on wellbore instability.
Advanced methods: Impact of faults on pore pressure prediction. Uncertainty, real-time updating and how real time updating reduces uncertainty ahead of the bit. Sub-salt pore pressure prediction. Impact of pore pressure on reservoir geomechanics - depletion and stress changes. Compaction and subsidence.
Exploration and development geologists, petrophysicists, geophysicists, drilling engineers, completion engineers and reservoir engineers who need an essential understanding of the impact of pore pressure on drilling, wellbore stability, and reservoir management.
Basic understanding of drilling, geology and geophysics. Basic understanding of risks associated with drilling operations.