A Technical Playbook for Chemicals and Additives Used in the Hydraulic Fracturing of Shales

Abstract

Improving production of shale gas and tight oil from low-permeability formations has dominated the energy landscape over the past two decades. Successful applications of horizontal drilling combined with hydraulic fracturing (HF) techniques, first demonstrated in the Texas Barnett shales in the 1990s, are the impetus for the current shale boom in the Americas. Chemicals are at the heart of the fracturing (or "fracking") process, which includes pumping a water-based fluid and proppant into a shale formation to create fissures that access the buried hydrocarbons. The fracturing fluid composition is critical to the completion design and should reduce wellbore friction while enabling proppant placement into the fractures. However, adding too many chemicals without properly evaluating the fracturing fluid formulation can lead to increased cost, poor fluid performance, or even damage to the reservoir. This review discusses the purpose of each chemical used in HF fluids, the techniques applied by the production chemist to assess fluid performance, and suggested best practices in optimizing formulations to reduce costs, enhance performance, and improve footprint.

Development and Evaluation of an Acidic Shear-Tolerant Nanosheet-Enhanced Cross-Linked Gel System for Hydrofracturing

“…The success of this operation depends on whether the fracturing fluid has satisfactory rheological properties and a suitable proppant carrying capacity . Many novel fracturing fluids, such as viscoelastic surfactants (VESs), slick water, supramolecular polymers, energized fluids, and supercritical carbon dioxide (CO 2 ), have been designed and developed through oilfield chemistry research. − Nevertheless, traditional guar-based linear or cross-linked fracturing fluids are still the most commonly used fluids in oilfields due to their desirable performances and low costs. − …”

“…Guar gum is a natural galactomannan polysaccharide derived from cluster beans, which are typically planted and grow well in semiarid areas (mainly India). − The chemical structure of guar gum consists of a linear backbone chain of beta-1,4-linked mannose residues, to which the short side chains of galactose residues alpha-1,6-linked are attached at every other mannose. − Typically, original guar gum has a low solubility in aqueous solutions and has poor temperature resistance and gel-breaking performance after cross-linking. To solve these issues, reagents such as propylene oxide and/or chloroacetic acid have been employed to modify guar gum, resulting in three guar-gum derivatives: hydroxypropyl guar gum (HPG), carboxymethyl guar gum (CMG), and carboxymethyl hydroxypropyl guar gum (CMHPG) . Borate cross-linked HPG and zirconium cross-linked CMHPG are two common guar-based, cross-linked gel-fracturing fluid systems that have been applied in different pH situations. − Carbon dioxide (CO 2 )-enhanced oil recovery (EOR) and storage techniques have broad applications in compacting reservoirs in China, such as the Changqing, Jidong, and Daqing peripheral oilfields. , CO 2 –water–rock reactions occur in the formation zone under high-temperature (HT)/high-pressure (HP) conditions, altering the pH of the formation environment; this pH can be as low as 3.5 .…”

“…To solve these issues, reagents such as propylene oxide and/or chloroacetic acid have been employed to modify guar gum, resulting in three guar-gum derivatives: hydroxypropyl guar gum (HPG), carboxymethyl guar gum (CMG), and carboxymethyl hydroxypropyl guar gum (CMHPG). 31 Borate cross-linked HPG and zirconium cross-linked CMHPG are two common guar-based, cross-linked gel-fracturing fluid systems that have been applied in different pH situations. 38−40 Carbon dioxide (CO 2 )enhanced oil recovery (EOR) and storage techniques have broad applications in compacting reservoirs in China, such as the Changqing, Jidong, and Daqing peripheral oilfields.…”

Viscosity-Reducing Agents (Breakers) for Viscoelastic Surfactant Gels for Well Stimulation

“…Polymers and viscoelastic surfactants (VES) are used to improve well productivity in carbonate and sandstone reservoirs. − These compounds are used in matrix acidizing and hydraulic fracturing. ,− In matrix acidizing, polymers and VES are used as chemical diverters and are known as self-diverting agents. ,− Using diverters ensures that the low viscosity acid pumped into the well goes into the low-permeability zones and not in the high-permeability zones, thus increasing the effectiveness of matrix acidizing. ,− , Diversion by gels replaces mechanical diversion techniques because mechanical diversion methods are not always recommended, especially for long horizontal or extended-reach wells. , In hydraulic fracturing, polymers and VES act as a fracturing fluid and a proppant transporter as a result of their high viscosity. ,,,, They are pumped at or above the formation fracturing pressure to create fractures in the wellbore, thus improving well productivity, especially in low-permeability zones . However, the usefulness of gels is not only based on their diversion or fracturing abilities.…”

Special Issue of Energy & Fuels Honoring Michael T. Klein

“…Veluswamy et al 12 present thermodynamic and kinetics of the formation of natural gas hydrates, which can serve to store large quantities of natural gas. Reynolds 13 describes how additives imbue the many, desired characteristics that fracking fluids must exhibit for them to be deployed effectively.…”