The Uinta Basin is known for its lacustrine depositional environment and its high lateral variance that makes it challenging to predict and characterize petrophysical properties. In this study, a formation evaluation workflow is presented that extracts geochemical and geomechanical data for a lateral section of horizontal well. Then the obtained data was benchmarked to production, completion and core laboratory testing data to identify the best landing targets.
For this case study, four wine rack placed wells were analyzed for geochemical and geomechanical properties. Wine rack wells were drilled in Uteland Butte and Wasatch formations within the Uinta Basin. First, high-resolution drilling cuttings were collected at pilot wells. Cuttings were analyzed for mineralogy using X-ray diffraction (XRD), elements using wavelength dispersive X-ray fluorescence (XRF) and total organic carbon (TOC) using pyrolysis. Subsequently, considering the geomechanical aspect, a stress profile was generated from well log data by assuming isotropic material. Young’s modulus and Poisson’s ratio values obtained from rock mechanic testing on the vertical core as well as DFIT results were used to validate the model. Utilizing the core’s mechanical properties and mineralogy, rock physics modelling was used to find the best theoretical bounds. The bounds can be implemented to predict mechanical properties using mineral composition from cuttings samples. Afterward, the stress profile from cuttings analysis can be compared with the geophysical log.
It was identified that the rock physics model of core data follows the Reuss-bound trend. It explains that the rock is layering horizontally, validating the isotropic assumption when calculating the rock physics model. Since the mineral composition of cuttings samples match the core, the Reuss model can be applied to the cuttings data to calculate rock mechanical properties and the stress profile. The generated stress profile from the geophysical log has less variability than the rock components, as the Biot’s coefficient is usually assumed as a constant. On the other hand, using a rock physics approach, the Biot’s coefficient can be predicted. In the Wasatch Formation interval, the stress profiles from both the geophysical log and rock components show that there is a stress barrier, which is more pronounced in the latter.
Completion strategies on the four horizontal wells are similar with the Uteland Butte wells showing the highest cumulative production. The low flowable hydrocarbon index explains the lower production on Wasatch wells. Moreover, the observed stress barrier prevents vertical growth of the hydraulic fracture which leads to less access to hydrocarbon.
This study shows that cuttings analysis provides valuable information and better decision input to identify more productive wells.