The process of building a Mechanical Earth Model using well data
Research output: Research › Master's Thesis
Modern well construction projects are technically and economically challenging. In order to complete the well in time and within budget the non-productive time which is associated with lost circulation, kicks, wellbore instability and anomalous pore pressure regimes has to be minimized. These issues are strongly related to the stress regime in the area. Therefore, a good knowledge of stress regime in the area of interest helps to mitigate the delay caused by the mentioned issues, consequently cost and risks are reduced. Using log measurements, a mechanical earth model (MEM) can be built so instability zones are predicted and issues avoided. The mechanical earth model is a numerical representation of the state of stress and rock mechanical properties for a specific stratigraphic section in a field or basin. The model is linked to geologic structure through the local stratigraphy and seismic data. In addition to property distribution (e.g. density, porosity) the model incorporates the pore pressure, state of stress and rock mechanical properties (e.g. UCS, friction angle, Young’s Modulus and Poisson’s Ratio). The stresses on the reservoir are caused by the overburden weight, any superimposed tectonic forces, and by production and injection. The properties are derived from various logs e.g. sonic log, density log using various methods. Before and during drilling the model is calibrated using core and pressure test results. After analysing rock failure, a safe mud weight can be recommended. At first, this work introduces the topic by discussing what a well-centric 1D-MEM is and the potential economic benefits are elaborated. In the second part, it presents the required equations and methods to derive rock properties from log data and other sources and explains how the stress state and a safe mud weight window not causing failure can be derived. In the third part the presented equations and methods are applied to an offshore well data and a MEM for that well is built. The modelling process is described and results are presented. Finally, the process, results and occurred problems are discussed. It closes by concluding problems and potential benefits of the MEM in general and discusses future potential of the method and possible research on it.