Predicting fluid pressure in reservoir formations, which are porous and permeable, and in shale formations, which are porous and largely impermeable, represents a major challenge for oil exploration. Reliable prediction of that pressure before operations begin can significantly reduce drilling costs and create safer conditions for teams. Building on our expertise, we are constantly refining our predictions thanks to calculation methods that draw on the full range of data available.
The Challenges Involved in Predicting Pore Pressure
Pore pressure is considered normal when it corresponds to a hydrostatic pressure regime determined by the freshwater or brine column that permeates the subsurface up to the surface. That is usually the case when it comes to relatively shallow drilling operations. In difficult environments, however — deep offshore, tight basins, high-temperature and high-pressure reservoirs — there is a greater risk of abnormal pressure levels. As a result, in order to choose the right drilling configuration and mud program, it is essential to have a reliable prediction of the pore pressure in the various formations before we begin operations, for two reasons:
- Safety. Drilling mud is the primary safety barrier between the bottomhole and the surface. So it’s critical to devise a mud program that prevents any excess pressure differential during drilling. An inaccurate assessment poses the risk of a blowout and loss of the well, with major human, material and environmental consequences.
- Cost. If the prediction is too high, drilling costs may increase substantially because of unnecessary casings, resulting in excessively high equipment costs and needlessly long drilling times.
Our Integrated Expertise for More Reliable Predictions
The Pore Pressure Prediction unit, established in 2008, is tasked with studying and predicting formation pressure levels during exploration. Boasting a success rate of over 90% out of 250 wells analyzed, the team anticipates pressure levels prior to drilling operations in order to determine the optimal configuration and mud program.
To predict pore pressure, our experts create models based on seismic velocities; abnormally high pressure levels suggest velocities that are lower than normal. The workflow encompasses a variety of disciplines and units: seismic processing and interpretation, regional and local geology, petrophysics, petro-elastics, sedimentology, basin modeling, geochemistry, analysis of petroleum systems and geomechanics. Our tools can leverage high-performance computing capacity and 3D seismic data interpretation thanks to the Pangea supercomputer.
Direct Prediction in Reservoir Formations: An Advance in Our R&D
The standard method works well for shale formations, but can’t be applied to reservoir formations, where pressure levels are determined more by mineral composition, porosity and fluid content. Up until now, predictions for reservoirs have relied primarily on geological conditions (the basin’s history, reservoir continuity, analogous formations, aquifer size, etc.).
So E&P launched an R&D initiative to predict formation pressure in reservoirs — an especially vital concern for an oil industry confronted with increasingly complex environments and reservoirs (subsalt, carbonate, etc.).
The resulting method, which involves the inversion of petro-elastic models (PEMs), can be used in a known environment, calibrated by wells, to obtain information on fluid pressure, based on petrophysical scenarios and velocity data. The new strategy was initially validated using logs, then successfully expanded to seismic data.
An operational prototype for clastic environments has been in development since 2017 and will be deployed in actual deep offshore drilling by 2020.