As a result of creating the model at each point of the well trajectory, the gradients of caving, pore pressure, absorption and fracture are determined along the entire section penetrated by the well.
The modeling process can be divided into several stages:
- Collection and audit of data. At this stage, we collect and analyze information on the investigated and neighboring wells. Well logging and seismic data, drilling history, core study results, geological and petrophysical models are analyzed.
The minimum set of initial data required to create a 1D geomechanical model:
- Daily reports
- Gamma ray logging
- Acoustic logging (p- and s-wave velocities)
- Density logging
- Petrophysical interpretation of the section
- Results of direct pressure measurements (LOT, FIT, MDT, etc.)
Data analysis is painstaking and important work - the predictive power of the model will depend on the quality of the data. There is a lot of manual work at this stage. It is necessary to view all daily reports and identify important moments in the history of the construction of offset wells, understand the geological features of the section, analyze and bring log data to a single format.
As the stage is completed, a single digital project is created in specialized software that contains all the initial information.
- Calculation of the parameters of the pivot well model. Based on the initial data, the model parameters are calculated for each pivot well: Young's modulus, Poisson's ratio, rock internal friction angle, pore pressure, values and directions of the main stresses. There are many methods for determining each parameter, so it is important to choose the one that best suits the given geological conditions and gives the best result.
- Calibration. Calculation results are calibrated according to actually measured data from borehole and core studies. Often, in order to obtain sufficient convergence of the calculated and measured values, it is necessary to return to the previous stage and make changes to the calculations. Modeling is an iterative process that requires an understanding of the physical meaning of each parameter, the ability to work with a large amount of logging data, and knowledge of calculation methods.
- Transfer of model parameters to the well under study. Producing well correlation and using the developed dependencies, the necessary parameters are calculated along the trajectory of the studied well.
- Building a window of combined gradients. The result of the calculation is a window of combined gradients of caving, pore pressure, absorption and fracture, expressed in terms of bulk density. This representation allows you to visually compare the simulation results with such important technological parameters as drilling fluid specific gravity and equivalent circulation density.
- Analysis of model sensitivity to parameter changes. Having built a model, it is possible to perform a sensitivity analysis, that is, to determine how the result of the calculation changes when any input parameter changes.
