In-Situ Water-Blocking Measurements and Interpretation Related to Fracturing Operations in Tight Gas Reservoirs

Abstract

Summary Invasion of aqueous drilling, completion, or fracturing fluids can reduce the relative permeability to gas and thereby causes a water block. In the case of low-permeability formations, the capillary pressure tends to be high because of the small pore size. Cleanup of water blocks requires high drawdown unless water vaporization by the flowing gas is improved by using specific additives such as alcohols. The purpose of this work is to investigate fracture-face damage by measuring relevant petrophysical parameters: absolute-permeability damage and gas return permeabilities. Measurements are performed in representative conditions of a fracturing operation in a tight gas formation: cores with an absolute permeability of 10 μd set at Swi and experimental pressure of 200 bars for the fracturing-fluid invasion. Water and gas saturations during the fracturing-fluid invasion and during gas backflow are monitored by X-ray equipment. Adding alcohol in the fracturing fluid has a striking effect on resolving water blocks. Cake formation on the simulated fracture face is also discussed. Numerical simulations are performed to assess relative permeabilities from the experimental results. It is shown that hysteresis of gas and water relative permeabilities has a strong impact on the rate of water removal. Sufficiently high pressure drawdown is crucial to overcome capillary forces and initiate the alcohol- assisted vaporization process. Water removal by water vaporization is assessed and compared to the experimental results.

Rate enhancement in unconventional gas reservoirs by wettability alteration

“…For core length L ¼ 0.1 m, permeability k varying from 0.01 to 10 md, gas viscosity m varying from 10 À5 to 4 Â 10 À5 Pa s, and pressure P varying from 5 Â 10 5 to 10 7 Pa, the maximum velocity where the incompressibility assumption is valid varies from 1.2 Â 10 À5 to 1 m/ s. The typical flow velocities in cores have the order of magnitude 10 À6 e10 À5 m/s (Barenblatt et al, 1990;Bazin et al, 2010). Therefore, gas compressibility is negligible under the conditions of these laboratory studies by Bazin et al (2010), so the incompressibility assumption is valid.…”

“…Therefore, gas compressibility is negligible under the conditions of these laboratory studies by Bazin et al (2010), so the incompressibility assumption is valid. For fractured wells, velocity at the fracture face is calculated using Eq.…”

“…In this section, the laboratory coreflooding carried out by Bazin et al (2010) under two flow rates are analysed in order to validate the model proposed in Sections 2 and 3. Cylindrical Môli ere sandstone core from tight gas reservoir with diameter of 3.8 cm and length of 7 cm is used.…”

Effect of Wettability Alteration on Productivity Enhancement in Unconventional Gas Reservoirs: Application of Nanotechnology

“…Laboratory coreflooding tests with two flow rates (Bazin et al, 2010) are analysed to validate the model developed in Section 3.…”

Advances in Understanding Liquid Flow in Gas Shales

“…Fracturing fluid imbibition into the rock matrix can severely damage absolute permeability through clay swelling and dispersion (Scott et al, 2007). Furthermore, in low-permeability reservoirs, capillary pressure can be several hundreds psi (Holditch, 1979) and therefore, fracturing fluid imbibition results in fluid retention (Economides and Martin, 2007;Dutta et al, 2013;Bazin et al, 2010). This process, called "water blocking", causes the relative permeability of gas to be reduced and thus decreases the gas production, dramatically (Shaoul et al, 2011).…”