Disproportionate Permeability Reduction of Water-Soluble Silicate Gelants - Importance of Formation Wettability

Abstract

Disproportionate permeability reduction (DPR) may provide field solutions to address high volumes of water production and efficiency of oil recovery in non-communicating layered reservoirs. This work evaluates the lab-scale DPR effectiveness at different formation wettability conditions using an environmentally friendly, water-soluble, silicate gelant. A robust, time/temperature stable and easy-to-design water-soluble silicate gelant system is utilized to conduct DPR treatments in oil-and water-wet cores using a newly established steady-state, two-phase chemical system placement. The experimental procedure is applied to ensure the presence of moveable oil saturation at which the injected DPR fluid (gelant) gels in the treated zone and to quantitatively control the placement saturation conditions in the formation. DPR treatments are conducted using a steady-state, two-phase (oil/gelant) placement to better control the water/oil saturation at which the silicate gel sets. The performance of water-soluble, silicate-based DPR treatments are evaluated using pre-and post-treatment two-phase (brine/oil) steady-state and unsteady state permeability measurements.Strongly water-wet Berea cores are chemically treated to alter their wettability to oil wet and measured phase effective permeability curves are used to characterize the newly established core wettability. Treatment design should include filterability/injectivity and rheological studies of the DPR fluid to evaluate gelant interaction with the formation as well as gelation time and kinetics. Single-phase DPR fluid injectivity through Berea cores is excellent. At relatively high watercuts in water-wet cores, two-phase DPR-fluid/oil injectivity is good and even better in oil-wet cores regardless the watrecut. At relatively low watercuts in water-wet cores, the injectivity is not as good as in higher watercuts and the mobility reduction keeps increasing with the co-injection of the DPR-fluid/oil. DPR-fluid/oil placement experiments conducted at the same saturation conditions and water/oil ratio (WOR) showed that the ultimate oil residual resistance factor in oil-wet cores is significantly lower than the one in water-wet cores. This is mainly due to more favorable oil-phase continuity and distribution in oil-wet media compared to the corresponding ones in water-wet formations. In water-wet cores, encapsulation of oil by gel may cause oil-phase discontinuities and porous medium conductivity reduction. Wettability tests have shown that silicate gel is strongly water-wet. Therefore, in oil-wet DPR treatments, formed gel in porous media yields a mixed-wet formation and a lower trapped oil saturation compared to the water-wet formation.In either wetting state, relative permeability hysteresis was insignificant during the post-DPR treatment imbibition/drainage cycles. This also reflects stable gels during post-DPR treatment floods. DPR treatments conducted at high WOR in oil-wet cores have shown a minor gel ЉerosionЉ during the post-treatment two-and single-phase (water) inje...

Rock/Fluid/Polymer Interaction Mechanisms: Implications for Water Shut-off Treatment

“…In other words, the RPM's swelling/shrinking characteristics depend on the flowing fluid phase that ultimately leads to DPR phenomena and aids in selective permeability reduction (SPR). [26][27][28][29]41,111,161,178,179,181,185,192,193 The factors that influence the RPM's swelling/shrinking phenomena are the following:…”

“…Type of Flowing Fluid (Water, Oil, or Gas). It has been reported that as water can defuse through the polymer/ gel layer, the water induces charge repulsion between the hydrolyzed groups in polymer/gel which in turn the polymer/ gel swells and subsequently resists the flow of water; 27,37,41,111,181,185,192 see Figure 14a. Furthermore, it has been stated that the mechanical force exerted by flowing oil/ gas fluid on polymer/gel causes water expulsion from the polymer/gel which eventually causes gel shrinkage; 22,23,30,33,41,45,46,111,160,181,182,185,194 see Figure 14b.…”

“…This in turn can lead to reducing the relative permeability of both wetting and nonwetting fluids. ,,,,, However, for plausible interpretation to DPR observations, it has been reported that water-based RPMs swell (hydrates) in the presence of water and, therefore, resist water flow while they shrink (dehydrates) in the presence of oil/gas fluid so that oil/gas flow easily. In other words, the RPM’s swelling/shrinking characteristics depend on the flowing fluid phase that ultimately leads to DPR phenomena and aids in selective permeability reduction (SPR). − ,,,,,,,,, The factors that influence the RPM’s swelling/shrinking phenomena are the following:…”

Potential of Low-Salinity Waterflooding Technology to Improve Oil Recovery

“…For a strong water-wet rock, the relative permeability curves will crossover at a wetting phase saturation point of greater than 0.5, while a strong oil-wet rock relative permeability curves will crossover at a wetting phase saturation point of lesser than 0.5. A crossover point at a saturation of 0.5 and equal end points of relative permeability curve imply that the reservoir rock is in neutral-wet condition [16].…”

Associative Polymers as Enhanced Oil Recovery Agents in Oil-wet Formations - A Laboratory Approach

“…Berea core samples are chemically treated to alter their wettability towards oil-wet (oil-wet or less water-wet depending on the treatment procedure). A summary of the wettability alteration process together with the wettability characterization of oil-wet cores are presented by Askarinezhad et al (2017a). The measured cores porosity and absolute brine permeability values are in the range of 21% -23% and 500 mD -900 mD, respectively.…”