Pore pressure models play a crucial role in the E&P workflow, from the early exploration phase to the final stage of field production. Pore pressure models and predictions are important in well planning and safe completion and also play a crucial role in field development and in reservoir management. Since most well design is based on pressure and temperature models, a wrong prediction can incur either a costly well or a hazardous situation, depending whether the model had over- or under- predicted the pressures. In a nutshell, pore pressure controls two of the major pillars of drilling activities – cost and safety.
As nothing works in isolation in this industry, the pore pressure expert works in conjunction with many factors to produce the perfect plan, so the team is a collaborative effort with input from all departments – interpretation geologist, geophysicist, petrophysicist, drilling engineers, reservoir engineers – to produce the most realistic and reliable result.
IMAGINATION WITH CONVICTION
A comprehensive pore pressure model will be the result of the collaboration of offset well data and analogue calibration; a basic understanding of well behaviour in relation to different geological settings controls the accuracy of pressure predictions. Since many exploration wells will need real time decisions based on the well behaviour and pressure models, it is much easier if an operations geologist with a pore pressure background is in command.
Ajesh John, Lead Operations Geologist for Cairn India, evaluates subsurface drilling data at a modern dual screen workstation. I started my career as a wellsite geologist where I came to understand the importance of pore pressure in a well, and gradually moved into pore pressure modelling. Over time, I have developed a core wellbore behaviour interpretation skill which is one of the main pillars of pore pressure modelling, particularly real time pressure prediction and well calibration. Since most pressure predictions are from petrophysical logs and seismic velocities, understanding rock properties and their relation to log and seismic response is vital in predicting the right kind of pressures.
Because I have this background I feel more confident, as it makes decision-making more accurate and helps me to manage operations with minimum errors and clear, effective communications with other departments. The basic understanding acquired through my years as a wellsite and then operations geologist have helped me blend the theoretical aspects to the ‘well’ reality. In many ways pore pressure modelling and its visualisation equates to imagination with a conviction. Like any model, a pore pressure model is not always accurate, but needs to be verified and upgraded with real time results to take the well forward and confidence is vitally important.
As a pore pressure specialist has to deal with multiple regimes and facets to come up with a reasonable model defining a well’s pressure attributes, there is no ‘essential background’ or training, but theoretical knowledge, technical expertise and extensive practical experience are all needed.
A geoscience background is essential to understand the subsurface geological processes while geophysical understanding allows the specialist to analyse the attributes/proxies which will be the backbone of the workflow. In addition, a thorough understanding of well bore behaviour analysis and calibration is needed, as is comprehension of geomechanics to help resolve complicated wellbore stability issues. The success of the pore pressure geologist greatly depends on the integration of all these disciplines with a holistic approach.
RESPONSIBILITY AND EXCITEMENT
The most interesting part about this job is the responsibility and excitement involved in the prediction. It involves a lot of imagination, knowledge of regional concepts and methodologies, good integration of the multidisciplines – and you actually get to see the impact and results of your models during drilling. Being an operations geologist, handling the pore pressure modelling makes me more responsible in terms of the predictions, as I am very aware of the negative or positive impacts of a predicted model. At the same time it gives me immense confidence to deliver my responsibilities efficiently knowing the pressure trends well in advance.
