A Study of Proppant Formation Reactions

Abstract

Based on long-term API conductivity data, proppants are generally chosen to optimize fracturing cost versus fracture conductivity. This long-term data is acquired by measuring conductivity for two days at simulated conditions of closure stress and reservoir temperature. It is recognized that the majority of the conductivity damage to a proppant pack occurs rapidly during the first day at simulated conditions. It is clear on examination of raw data that conductivity has not reached equilibrium after two days of flow, but rather it is still declining. Investigators who have studied the effect of longer flowtime on fracture conductivity of proppants have all concluded that the decline in conductivity continues for a much longer time.Much attention has been given to the mechanical properties of proppants to aid in the selection of the best material for a particular fracture treatment. These properties include: size, proppant-size distribution, sphericity, hardness, crush resistance, and acid solubility. Other than acid solubility, little information about the chemical reactivity of the proppants has been noted. Recent work has demonstrated that, at some reservoir conditions, certain proppants become significantly chemically reactive.This paper presents the proppant as starting material for geochemical reactions with various aqueous fluids saturated in typical formation minerals. Methods have been developed for rapid testing of these interactions, and test results clearly demonstrate how important proppant chemical reactivity is as losses in proppant-pack permeability of 50-90% were obtained, owing to the genesis of cementatious and porosity-filling minerals. In addition, some proppant chemistries were found to be much more susceptible to these types of reactions, losing much of their mechanical strength in a surprisingly short period of time. Results from this study indicate that operators who rely solely on API test methods in evaluating the suitability of proppants for particular downhole conditions might miss significant damage potential from geochemical reactions occurring between the proppant and formation fluids.

Mechanics of light weight proppants: A discrete approach

“…Research efforts are also on to study the influence of chemical reactions between the fracturing fluid and the proppant which is known as proppant diagenesis on pack permeability [58]. A modification to the conductivity test wherein an arrangement is made to collect loose proppant and measure their flow rate is used to study proppant flowback.…”

“…Fracture is assumed to initiate when the principle stress in tension exceeds the failure stress in tension. The single particle tests on spherical brittle ceramic particles can be used to determine the failure stress for the ceramic material as σ f = 2.8F failure /(πD 2 ) [58,79]. Here σ f is the failure stress in tension, F failure is the load measured by the load cell at the point of particle fracture and D is the particle diameter.…”

“…The Weibull statistical analysis is employed to characterize the mechanical response for the ceramic particles [58].…”

“…According to the procedure as described in [58] for each of the 36 particles tested we get a specific diameter, failure load and hence tensile strength. These 36 data points are then sorted in an ascending order of their strength.…”

Hydraulic stimulation of a deep sandstone reservoir to develop an Enhanced Geothermal System: Laboratory and field experiments

“…Although a variety of fracture damage mechanisms such as fluid invasion (Cinco-Ley and Samaniego-V., 1977;Romero et al, 2003), chemical interactions and clay swelling (Lynn et al, 1998;Moghadasi et al, 2002;Nasr-El-Din 2003;Weaver et al, 2009), particle transport and filtrate invasion (Veerapen et al, 2001;Al-Abduwani et al, 2003) and proppant pack permeability alteration (Wen et al 2007) have been investigated, hydraulic-mechanical interactions at the fracture face have not been studied.…”