INFLUENCE OF GEOLOGICAL FEATURES ON HYDRAULIC FRACTURE PROPAGATION

Understanding the created fracture geometry is essential to the effectiveness of any stimulation program. Geology is a fundamental element in the design of a stimulation program and in the interpretation of its results. Rock properties govern the types of fluids injected into the formation as well as the pumping schedule. Lithology dictates the location of the monitoring device, the location of perforations, and how hydrocarbons flow into the wellbore. Despite these facts, the geological impact on the stimulation results is often overlooked because it is commonly assumed that induced fractures have a symmetric planar geometry.

First, we present a review of the various hydraulic fracture diagnostic methods available depending on the information sought. Indirect hydraulic fracture diagnostic technologies are very well established and provide an overall idea of the stimulation results. Nevertheless, they are limited because the solutions are nonunique and require calibrations. Direct near-wellbore diagnostic techniques are commonly used because they are easy and relatively inexpensive to implement. However, their radius of investigation is limited to a few feet around the wellbore. Direct far-field diagnostic methods (e.g., microseismic mapping, tiltmeter mapping) provide accurate information on fracture development and geometry. The distance between observation well and observed fracture system should remain within 2000 ft.

Second, we present results of hydraulic fracture stimulations in various geological environments that have been monitored using microseismic data combined with both indirect and direct near-wellbore fracture diagnostic methods. We illustrate with these case studies that, in some instances, basic radial and planar fracture systems are generated as predicted by simple modeling techniques. However, in most cases, the final fracture system geometry is asymmetric and largely governed by geologic discontinuities such as joints, faults, and bedding planes. These geologic discontinuities significantly affect the overall geometry of the hydraulic fracture system. This can limit the fracture system’s development, increase fluid leakoff, hinder proppant transport, or even create a complex fracture network. Ultimately, such factors will affect well productivity.