Abstract
Unconventional shale-gas reservoirs are usually highly laminated with vertical and lateral heterogeneity. The elastic mechanical properties are highly anisotropic along the different orientations parallel and perpendicular to the bedding. The formation heterogeneity, elastic anisotropy, and structural complexity affect the stress field both near and far from the wellbore and thus the fracture containment, fracture initiation pressure, and breakdown pressure. A better understanding of the formation properties and in-situ stress can be achieved by an advanced logging program. Many studies have shown improved production in the lateral wells by implementing an engineered completion design using advanced sonic logs and other high-tier logs. The importance of understanding these properties in the lateral wells also raised questions including whether we can predict lateral log responses from pilot wells and whether the formation is laterally homogenous.
In this study, we compared the projected lateral logs from pilot wells with the actual lateral logs to shed insights on the important question of formation heterogeneity. Different techniques were applied including a gamma ray method and an advanced 3D near-well structural model. The 3D model took advantage of the valuable information from borehole geology interpretation of image logs such as bedding, fractures, and faults to build high-resolution near-well structures. It was then used as a framework to model the reservoir properties and far-field stress using methods including a layer-cake and a finite-element approach. The output of the model showed the lateral heterogeneity of the reservoir by comparing the lateral section with the pilot well.
The reservoir properties from these techniques described above were then incorporated and evaluated as part of the completion design workflow, which focused on both near-wellbore and far-field modeling. The results showed the benefits and limitations of each propagating modeling technique for optimizing the completion design and shed light on the realization of being able to project the pilot logs across a single horizontal well or an entire pad.