New Integrated Approach for Updating Pore-Pressure Predictions During Drilling

Abstract

AbstractThis paper presents a new integrated approach for updating pore pressure predictions during drilling of a well. Pore pressures in sedimentary rocks can vary from hydrostatic (normal) pressures to very high (abnormal) overpressures. Sediment pore pressures are important constraints that need to be carefully considered when planning a new well and will influence drilling strategy, casing program, and mud-weights.A pre-drill prediction of pore pressures is used as input in the well planning phase and is based on an assumption of the local geology in the prospect, typically extrapolated from near-by wells. However, the pre-drill prediction may be inaccurate or erroneous due to incorrect assumptions.To help solving this problem we have developed an integrated approach for updating the pore pressure prognosis during drilling. The methods for pore pressure predictions are integrated with an eDrilling system for real-time simulation of the drilling process. Data from the drilling operation are processed real-time and includes drilling parameters, logging while drilling data, and other measurements performed during drilling. The base for a real-time update is pre-drill pore pressure predictions from basin modeling using Monte Carlo analysis. As drilling and log data becomes available during the drilling operation, fast calculations of pore pressure along the well are performed. The calculated pressure along the well is used to weight the pre-drill Monte Carlo results in order to update the pore pressure prediction ahead of the bit.Real-time updated pore pressure predictions are of vital importance for advanced computer based systems for online supervision and decision support during drilling. Early warnings can be supplied if abnormal overpressures are to be expected ahead of the bit, or if measures should be taken to avoid dropping below the pore pressure. This paper presents the methodology and simulation results using log data from the Norwegian North Sea. Simulations show that pore pressure predictions ahead of the bit are improved compared with the pre-drill predictions, when updating predictions using the drilling logs.The novel combination of automatically updated pore pressure data during drilling with an advanced real-time integrated drilling simulator provides a powerful tool for next generation drilling software.