Gas Engineering by James G. Speight

Author:James G. Speight
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2021-08-10T05:26:32.962000+00:00

6.3.4

Fracturing fluids

Initially, the fluid is injected that does not contain any propping agent and is injected to create a fracture that is multi-directional and spreads in several directions. This creates a fracture that is sufficiently open for insertion of the proppant, which is injected as a slurry – a mix of the proppant and the carrier fluid and proppant material. In shallow reservoirs, sand is often used can be used and remains the most common proppant but in deep reservoirs, ceramic beads (in place of the usual sand proppant) may be used to prop open the fractures. Once the fracture has initiated, fluid is continually pumped into the wellbore to extend the created fracture and develop a fracture network.

However, each formation has different properties and, therefore, diffident in-situ stress forces are operational so that each hydraulic fracture project is unique and must be designed accordingly by identification of the properties of the target formation including estimating fracture treating pressure, amount of material and the desired length for optimal economics. Furthermore, the fracturing fluid should have a number of properties that are suited to the properties of the formation, such as: (i) compatibility with the formation rock, (ii) compatibility with the formation fluid, (iii) suitability to generate sufficient pressure drop down the fracture to create a wide enough fracture, and (iv) a sufficiently low viscosity to allow clean-up after the treatment.

Water-based fluids are commonly used – slickwater is the most common fluid used for shale gas fracturing, where the major chemical added is a surfactant polymer to reduce the surface tension or friction, so that water can be pumped at lower treating pressures. Other fluids that have been considered are oil-based fluids, foams, and emulsions but caution is advised when using non-aqueous fluids since these fluids must be allowable for injection (by regulation) and must not have any detrimental effect on the environment.

Additives for fracturing fluids are chosen according to the properties of the reservoir and include (Table 6.3): (i) polymers, which allow for an increase in the viscosity of the fluid, together with crosslinkers, (ii) crosslinkers, which increase the viscosity of the linear polymer base gel, (iii) breakers, which are used to break the polymers and crosslink sites at formation temperature, for better cleanup, (iv) biocides, which are used to kill bacteria in the mix water, (v) buffers, which are used to control the pH, (vi) fluid loss additives, which are used to control excessive fluid leak-off into the formation, and (vii) stabilizers, which are used to keep the fluid viscous at higher temperature. However, it must be emphasized that additives are used for every site and in general as few additives as possible are added to avoid potential environmental contamination (use of the additives must be controlled) and production problems with the reservoir.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.