Experimental Investigation of Proppant Diagenesis

Abstract

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.

Micromechanical Behavior of DNA‐1A Lunar Regolith Simulant in Comparison to Ottawa Sand

“…Journal of Geophysical Research: Solid Earth are minor abrasions visible on their surfaces which might be due to the sediment transportation (Ghosh et al, 2014). Similar abrasions were also observed by Sandeep, He, et al (2018) on the surfaces of river sand grains from Guangdong Province, China.…”

“…Ottawa sand grains can be classified as subprismoidal to spherical with rounded to well‐rounded shape according to Powers () chart. The grains are relatively smaller in size compared to DNA‐1A, and there are minor abrasions visible on their surfaces which might be due to the sediment transportation (Ghosh et al, ). Similar abrasions were also observed by Sandeep, He, et al () on the surfaces of river sand grains from Guangdong Province, China.…”

Effect of Proppant Damages on Fracture Conductivity and Long-Term Recovery in Shale Gas Reservoirs

“…17−20 Proppant diagenesis refers to any changes in the proppant particles after proppant placement. 21 This process is generally thought to proceed slowly, over geologic time. 22 Mineral precipitates during the rock−fluid and proppant interaction were observed, and the term "proppant diagenesis" was coined.…”

“…Proppant diagenesis refers to any changes in the proppant particles after proppant placement . This process is generally thought to proceed slowly, over geologic time .…”

“…The three processes along with the associated change in geometry result in changes in porosity and permeability with time. , Proppant diagenesis is investigated through both furnace and quad-cell experiments; at in situ temperature and compaction in a diagenetic reservoir, the proppant pack porosity and permeability decrease significantly . According to an experimental study, permeability dropped by about 99% in 10 days for Ottawa sand, ceramic proppants showed less drop in permeability, while resin-coated proppants did not show any permeability drop because the resin held the fines in place in Barnett shale reservoir for up to 60 days . Experimental investigations of diagenesis of bauxite, ceramic, sand, and resin-coated sand proppants in calcite-rich Eagle Ford shale fractures for mineral overgrowth and dissolution was conducted by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). , According to this work, sand- and resin-coated sand proppants did not show any overgrowth or precipitates from the proppant diagenesis process.…”