The successful drilling of horizontal wells is extremely difficult, mainly due to lithological discontinuities and seismic uncertainties. To overcome such challenge, Well Placement technique is used to interactively position the well based on geological and seismic criteria together with LWD measurements. While covering drilling, geology and geophysics, most Well Placement approaches rarely consider reservoir engineering aspects. This paper presents an innovative methodology that integrates reservoir engineering into Well Placement workflow to improve well's productivity performance.
The applied method is based on advanced 3D modelling, where by means of numerical reservoir simulations, productivity predictions are performed not only on the planned well but also at the executed trajectory. To increase prediction accuracy, a refined gridding with variable cell size technique is applied to enhance pressure and saturation sensitivity. The level of precision is improved by using LWD measurements, such as most precise formation pressure, permeability near wellbore and remote boundary mapper technology that provides a detailed reservoir structure based on formation resistivity contrast.
This methodology was employed in a real case study of a horizontal well drilled in an offshore sandstone field in Brazil. As common occurrence in Well Placement operations, the executed trajectory had significant geometrical differences compared to the planned one. For both planned and executed wells, a detailed reservoir model was created using the inputs of LWD measurements. Numerical simulations were then applied to both wells in order to evaluate the impacts caused by the trajectory variations, showing the expected productivity results versus the actual ones obtained at the drilling operation. The results demonstrated indeed a major productivity impact in all reservoir fluids when a well trajectory is subjected to geometrical changes. However, only through the use of this integrated approach could such impact be quantified, since the traditional Well Placement methodology cannot determine the effects on the productivity response based only on the geological and petrophysical aspects.
The work delivers a novel ability to construct optimal horizontal wells not only by including conventional Well Placement technique, using geological and geophysical criteria, but also by introducing into the workflow an advanced numerical simulation approach. Such integration allows the operator to predict the impacts on the productivity as the trajectory is being changed, and the actual reservoir geometry and its properties are determined by LWD measurements.