Surface-Area vs. Conductivity-Type Fracture Treatments in Shale Reservoirs

Hydraulic fracturing continues to be the primary mechanism to produce hydrocarbons out of tight shale reservoirs. Ever since the success of the Barnett shale program, operators are inclined to pump similar large-volume water-fracture (waterfrac) treatments with little or no proppant in their respective shale plays. This assumes that all shale plays are the same and react accordingly to large-volume treatments. The basic objective behind such treatments is to contact large surface area, which has been very successful in the Barnett shale play. Such large-volume treatments in other shale plays may not be an optimized solution for the specific shale attributes, and the response may lead to uneconomical production results. Some shales might require a conductivity fracture treatment on the basis of their reservoir characteristics. So, it is important to understand the characteristics of these shales before deciding on the stimulation treatments. In addition to core and log analysis of these shales, fluid-sensitivity tests, Brinell hardness (BHN) tests, unpropped-fracture-conductivity tests, and, more importantly, a diagnostic fracture injection test (DFIT) can help define the guidelines for choosing between a surface-area and a conductivity-type fracture treatment. Integrating the various data sources is important in arriving at these guidelines. The main objective of this paper is to provide these guidelines alone with examples so that a costly trial-and-error approach for stimulating shales can be avoided. Examples from both oil and gas shales (i.e., the Gothic, Haynesville, Eagle Ford, and Barnett shale plays in the USA) are included in this work.