A Novel Hydraulic Fracturing Technique Greatly Improves Hydrocarbon Recovery Through the Use of Temporary Beneficial Changes in Stress Anisotropy
Authors: Surjaatmadja Jim B. , Lewis Bryan J. 
Published: October 2015

The effects of the earth's tectonic movements are well understood, especially in the formulation of stress anisotropy in a large region. This primarily mechanical effect stays unchanged because the support systems, such as faults, compressions, etc., remain unchanged until the next major tectonic activity. On the other hand, pressure effects are generally semi-permanent and are usually affected by the production history of the formation. In this stress domain, fracture placement during a stimulation treatment will always follow the direction of maximum stress; by definition, this is a fixed direction defined by the known stress anisotropy landscape.

This paper presents a different approach for the stimulation process. Instead of a conventional, static, or end-point vision of the stimulation, a dynamic, or temporary, time-dependent stimulation method is introduced. The new method creates a small tectonic motion—significantly smaller than that of natural tectonics—and uses it to temporarily modify the local stress anisotropy. The "micro" tectonic motion is created by means of a conventional fracture placed in the natural maximum stress direction. Another fracture can then be created using the same approach but in a temporarily modified stress field that forces it in a different fracture direction. This new multioriented hydraulic fracture (MOHF) stimulation method can enhance state-of-the-art hydraulic fracturing technology by requiring an understanding of the transient geomechanic response in the treatment area.

As a time-dependent method, this approach can create new opportunities in both conventional and unconventional plays by providing connectivity to previously unattainable locations in the formation. Unfortunately, it can also result in new complications. Industry standard fracture simulation technology becomes incomplete, as most models neglect the transient response of the system. Additionally, the availability of data related to the dynamic behavior of rocks is limited. The dynamic compression of the rock, slip characteristics between rock layers, and the amount of energy stored within slip planes—all recorded as a function of time—are particularly important when considering an MOHF process. Additional testing should be performed to obtain these data. With such data, time-sensitive operational recommendations for performing the MOHF stimulation can be provided to help achieve the maximum production increase from the well.

This paper also discusses a computational validation of the MOHF process. As traditional hydraulic fracture simulations are derived using static formation properties and steady-state assumptions of the formation behavior, a unique transient three-dimensional (3D) computational geomechanic fracture simulator was developed to perform this study. The new model incorporates cohesive zone elements to represent the fracture plane and captures the dynamics of fracture initiation and propagation, as well as the transient stress modification in the formation. A realistic 3D fracture transient behavior is accounted for by the inclusion of multiple rock layers in the model, which are connected through energy absorbing frictional elements. Production levels of two to five times greater were predicted using reliable production simulators.