Integrating 4D seismic data into dynamic characterisation of an HPHT reservoir

Abstract

During the production of a high-pressure and high-temperature reservoir, massive pressure depletion happens giving rise to geomechanical changes which can lead to dangerous events for field development, such as fault reactivations and well failures. Therefore dynamic reservoir characterisation and monitoring is very important for this type of reservoirs. In this thesis, I use time-lapse time-shifts observed between 4D seismic surveys for the integrated study on dynamic characterisation of the Shearwater field which is a high-pressure and high-temperature field in Central North Sea. This thesis consists of two parts. Before using time-shifts for reservoir characterisation, they need to be accurately calculated. In the first part, I present a critical comparison of three different types of methods (DHFCC, CLM, and NLI). With applications to a set of synthetic and real time-lapse seismic data of various quality and time-shift magnitudes, the advantages and disadvantages of each method have been revealed. I have found that all the time-shift methods can successfully measure time-shifts. Among them, NLI is the most outstanding method as it gives smooth time-shifts with relatively good accuracy and the time-strains derived from there are more stable and interpretable. In the second part, I perform the dynamic reservoir characterisation. Firstly, time-shifts are generated using the three methods and are then interpreted by linking them with geology and production patterns. The measured time-shifts essentially have the same distribution and magnitude. They can be generally correlated with field geology and production volumes. Furthermore, by taking derivation, four time-strain anomalies are identified in some overburden and underburden formations. In the following work, I perform the geomechanical modelling and the evaluation of overburden gas and geomechanical effects, trying to understand the physics behind these anomalies. I have found that most of the anomalies can be modelled by closely linked with geological patterns. The large overburden time-strain is mainly due to geomechanical effects rather than fluid changes. Apart from that, the constructed geomechanical model has also been calibrated and updated using time-lapse time-shifts, and is useful for analysing the evolution of stress and strain fields in order to predict potential failure events. Overall, my PhD research has successfully measured, interpreted and applied time-lapse time-shift, and has demonstrated its good value in dynamic reservoir characterisation.