Comparative role of mechanisms such as proppant crushing, embedment, diagenesis and fines migration is not well understood regarding hydraulic fracture conductivity. In this study, we have measured the long term permeability changed in the proppant pack under downhole conditions of temperature, confining pressure, pore pressure and fluid salinity. Major part of this study investigates proppant diagenesis and its role in hydraulic fracture conductivity reduction. Diagenesis is defined as any change in the proppant/shale material after proppant placement. Proppant indentation on the shale surface was also studied along with changes in chemical composition of the exit brine.

Diverse types of secondary growths were observed both on the proppant as well as the shale surface. Most of the secondary growth using the quartz proppant and low flow rate was observed near the shale edges where the brine velocity was low. Ceramic proppant showed the most secondary growth, while resin coated proppant showed no growth. The pH of the exit fluid of several tests show dependence on carbonate content of shale. Significant permeability change that was observed with high flow rate tests was not observed at low flow rates. For quartz proppant, considerable amount of proppant breakage and indentation was observed. Fines generation causing permeability reduction was observed in tests conducted with quartz and ceramic proppants but not resin coated proppants. Indentation depth showed dependence on proppant type and distribution.

Introduction

Hydraulic fracturing is conducted to create a pathway for the hydrocarbons to flow into the wellbore from the reservoir. Fracturing fluid under very high pressure is pumped along with proppants during this procedure. While the high hydraulic pressure helps in fracture initiation and propagation, the proppant helps in keeping the fracture open after pressure removal for easy flow of hydrocarbons. Economic production from shales is attributed mainly to hydraulic fracturing. Shales exhibit very low permeability, usually in the range of 10-1000 nanodarcies. At such low permeability, the use of multistage hydraulic fracturing is inevitable. Proppants are pumped during the hydraulic fracturing process. Their interaction with the shale matrix and the surrounding liquid is important to understand because this governs the long term permeability of the fracture. This paper discusses the results of long term studies conducted at simulated reservoir conditions to study the proppant behavior and associated fracture permeability.

This content is only available via PDF.
You can access this article if you purchase or spend a download.