Insights into Surfactant Containing Fracturing Fluids Inducing Microcracks and Spontaneously Imbibing in Shale Rocks

Abstract

Surfactants are typically added into fracturing fluids to assist flowback and/or enhance oil and gas production from liquids-rich shale formations. Two primary benefits that can be overlooked are the potential capability of surfactants to initiate microcracks near primary fractures and spontaneous imbibition farther into the formation rocks. With the additional initiation of microcracks and access to hydrocarbon reserves, initial production can be enhanced and production declines, over time, can also be mitigated.In this study, new mechanisms for surfactants to initiate microcracks and accelerate crack growth are proposed in which the speed of microcrack propagation could be controlled by the rate at which surfactant is advected to the crack tip by means of induced Marangoi flows (Vella et al. 2006). The accelerated crack growth is related to a decrease of the crack surface energy enabled in the presence of surfactant.On the other hand, a new mechanism has been previously proposed for increasing the contact area between fracturing fluids and the matrix. The working hypothesis is that a surfactant, when properly tailored to treatment fluids, can spontaneously spread in the matrix and access additional hydrocarbon reserves.The data indicate that fracturing designs could be further optimized by using a surfactant to activate more cracks. The shut-in time immediately after fracturing also could be crucial for enhanced well productivity. An extended shut-in time could result in the additional initiation of microcracks, farther penetration of fracturing fluids into the matrix, and greater oil recovery in liquids-rich shale plays.

Gypsum-Crystallization-Induced Fracturing during Shale–Fluid Reactions and Application for Shale Stimulation

“…These fractures provide a channel for oil and gas to flow through, thus increasing the amount that can be extracted. For a typical hydraulically fractured shale formation, the complex fracture network consists of primary fracture (on the scale of millimeters in size) and secondary microfracture (on the scale of nanometers to micrometers in size), and the latter may be more important to efficiently extract the oil and gas from shale matrix, because of its extremely low permeability. − In the conventional hydraulic fracturing treatments, a dense secondary fracture network requires the optimum conditions of pump rate, fracturing fluid volume and viscosity, in situ stresses, the presence of natural fractures and their distribution, mineralogy, and so on. ,− To decrease the costs of shale fracturing and improve treatments efficiency by the additional initiation of microfractures, some new methods were proposed in the past five years, such as clay swelling-induced microfractures, − using surfactants or other chemicals to accelerate crack growth, − and thermal reactivation of natural microfractures . Because of the absence of sufficient experimental evidence and quantitative estimates of the induced stresses, however, it is still unclear whether it would be likely for generation of induced microfractures to occur in shale formations with compressive effective stresses above several tens of megapascals.…”

Chemical and Reactive Transport Processes Associated with Hydraulic Fracturing of Unconventional Oil/Gas Shales

“…In addition, surfactants in HFF can directly affect the initiation of microcracks and crack growth rate. , Specifically, hydrophilic and hydrophobic interactions of hydroxyl groups and methyl groups, respectively, of the surfactants with the crack surface in addition to the electrostatic interaction between the ionic head groups of the surfactants can result in stress-enhanced chemical reactions. By relating the crack-growth rate to the surface energy, nonemulsifying surfactant blends were found to inhibit and even prevent crack growth in organosilicate thin films, which was attributed to the inferior surface-wetting properties compared to ionic surfactants.…”

Performance analysis of chemical flooding in fractured shale and tight reservoirs

“…In terms of EOR methods, gas injection, especially huff‐n‐puff gas injection, has been extensively studied (e.g., Sheng and Chen, Sheng, Wan et al, Yu and Sheng, Yu et al, Meng and Sheng, Meng et al, Li and Sheng, and Sharma and Sheng). Although water injection may not be as effective as gas injection, many efforts have been made to add surfactants in water and fracturing fluid for the EOR purpose (e.g., Shuler et al, Wang et al, Xu et al). Those authors studied spontaneous imbibition of surfactant solution in to shale or tight rocks.…”