In-Situ and Induced Stresses in the Development of Unconventional Resources

Abstract

Multistage hydraulic fracture stimulation of horizontal wells often results in asymmetric hydraulic fractures, which are suboptimal for draining reservoirs. Field observations suggest that hydraulic fractures grow further than expected toward, and sometimes up to and beyond, adjacent producing wells. Such interference from nearby wells is of increasing importance in densely drilled unconventional reservoirs, where hydraulic fracturing is common. Eventually, the underlying mechanism needs to be factored into well spacing plans and hydraulic fracture treatment designs, which can either mitigate the undesired consequences of the nonvirgin conditions, or take advantage of them.An integrated approach has been developed to quantify depletion-induced stresses. In this approach, a three-dimensional (3D) Mechanical Earth Model (MEM) is constructed using the finite-element method to initialize the in-situ stresses. Coupled simulation between the dynamic reservoir model and the geomechanical model is used to quantify stress variation, induced by pressure depletion of the parent well. The altered stress profile is then used as input to a hydraulic fracture design.The methodology has been applied to an unconventional resource play in the Williston Basin in North America. In this example, three adjacent horizontal wells were hydraulically fractured and put on production sequentially within four years. The analysis indicated that the minimum horizontal stress decreased in the area between a newly drilled well and the nearby producing well; whereas the area on the opposite side of the new well showed no obvious stress variations. Formations above and below the depletion zone experienced an increase of minimum horizontal stress as a balance effect of the finiteelement calculation. Fracture modeling using the depletion-induced stresses showed that the effective half-length of the fracture directed toward the depleted well can extend up to two times the length of the hydaulic fracture in the opposite direction.

Impact of elliptical boreholes on in situ stress estimation from leak-off test data

“…In an oilfield subjected to injection or production activities, stresses vary due to volumetric strain changes. This has been found in conventional resource reservoir deformation and casing stability analysis (Geertsma 1973;Safai and Pinder 1980;Segall and Fitzgerald 1998;Du and Olson 2001;Soltanzadeh and Hawkes 2008;Han and Dusseault 2008), caprock integrity analysis (Han et al 2012;Rahmati et al 2014), and completion of unconventional resources (Nagel et al 2013;Han et al 2014). In petroleum engineering, especially in development of unconventional resources, effective determination of in situ stress is critical to ensure successful drilling, quality completion, and reservoir containment analysis.…”

Investigation of the Impact of Natural Fracture Geomechanics on the Efficiency of Oil Production and CO2 Injection from/to a Petroleum Structure: A Case Study

“…The subject of geomechanical effects in fractured reservoirs is addressed in several papers. The most numerous group of the papers refers to unconventional reservoirs in the aspect of their hydrofracturing or refracturing [48][49][50][51][52]. Another group of papers is focused on CO 2 sequestration cases in aquifers [53,54].…”

Review and simulation of passive seismic tomography in block cave mining

“…This has a material impact upon safety and production. Movement along structures and rock deformations affect abutment stress distribution conditions (Han et al 2014). Therefore, it is relevant to track rock mass deformation in the early stages of potential failures in order to mitigate ground movement hazards, which benefits both safety and production.…”