Abstract

We have been conducting shale research for more than four decades in Oilfield as well as Coal mines. Since late 1960s, our work has dealt with troublesome shale as a source of well bore instability or coal mine roof falls near ventilation shafts. We quickly found that the shale issues must be addressed by simultaneously taking into account the combined chemical, physical, and mechanical properties of the shale. To accomplish this, we introduced the thermodynamic properties of the shale based on its specific percentage of clay content. This technique, along with sound and practical petroleum engineering practices, guided us to successfully design the mud systems, tailored for drilling long sections of troublesome shale, and resolve the issues of well bore instability, ultrafine contamination, lost circulation, slow drilling. In addition to considering shale as a source of hazard, since mid 1970s, we have been involved with research that considers shale gas/liquid as a viable economic resource and how to best extract these natural energy resources from shale that could be categorized as "troublesome shale."

In this work, regarding the recovery of the natural energy resources, we share our recent results and conclusions about the following questions and their significance to both Roof Control in Coal Mining and Petroleum Engineering:

1. Shale in contact with water vapor: Application to Mining Engineering, specifically to Roof Control in Coal Mining near the ventilation shaft or the main shaft, we answer questions related to interaction of water vapor appearing in ventilation system and shale

• Is there any water in the gas shale that seemingly appears dry?

• How do the micro-fracture networks in shale grow?

• At what specific sites do these micro-fracture networks initiate?

• Why these micro-fractures do not develop in some specimens that have almost the same type and concentration of clay minerals?

• What kind of fracture develops in these networks?

2. Shale in contact with water: Application to Petroleum Engineering we answer questions dealing with immersion of shale in water:

• At what specific sites is the gas stored within the shale mass?

• Could there be any relationship between the activated sites of "free gas," which may result in the development of localized "pore pressure" in the "pickled" shale mass and the appearance of the fault within the same specimen?

• Is the fault appearing in the "pickled" shale specimen strictly a normal fault?

• How many types of gas flow behavior can we expect from the "pickled" gas shale?

• Is the gas flow from the "pickled" gas shale cyclic within a short time or steady over long periods?

• For how long, at a minimum, should we shut-in the well after hydraulic fracturing for optimal gas production results?

To answer the above questions we find that we need to understand what shale is before dealing with it as a resource material or control it when it poses engineering issues.

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