Mud weight selection based on the overburden thickness variability on a wellbore-scale geomechanical model for unconventional clean energy reservoirs, San Juan Basin, Colorado.

ABSTRACT: Accurate prediction of the vertical stress plays a fundamental role in defining the mud weight window in horizontal wells when the overburden thickness changes along the wellbore trajectory due to topographic features. The proper solution for modeling the vertical stress along the planned wellbore is building a 3D model; however, the lack of seismic data to perform geomodeling horizons and key measurement interpretations, such as density and/or velocity waves, challenges this approach. In this study, carried out in the San Juan Basin for Fruitland Coal, we used the wellbore trajectory planned, the overburden length from the topography to the coal bed, and the constrained mechanical earth model built in the area to estimate the key input data to predict the expected mud weight window. The mud weights generated from the model highlighted several challenges, particularly in two main hazards: mud losses and borehole restriction risks. Understanding the mud weight outputs has allowed the operator to design pre-drill drilling parameters, improve mud system schedules, and maximize lateral lengths while assessing wellbore instabilities, allowing them to be prepared for an early total depth. This simple flag has reduced capital expenditures for rig time, improved mud system, and helped downhole tool losses.