Modeling the Impact of Capillary Pressure Reduction by Surfactants (2007)

Modeling the Impact of Capillary Pressure Reduction by Surfactants Rick David Gdanski Rick David Gdanski Halliburton Energy Services Group Search for other works by this author on: This Site Google Scholar Paper presented at the International Symposium on Oilfield Chemistry, Houston, Texas, U.S.A., February 2007. Paper Number: SPE-106062-MS https://doi.org/10.2118/106062-MS Published: February 28 2007 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Gdanski, Rick David. "Modeling the Impact of Capillary Pressure Reduction by Surfactants." Paper presented at the International Symposium on Oilfield Chemistry, Houston, Texas, U.S.A., February 2007. doi: https://doi.org/10.2118/106062-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE International Conference on Oilfield Chemistry Search Advanced Search AbstractFluid recovery after fracturing treatments in tight gas reservoirs is often critical in obtaining maximum production rates. Fluid recovery aids in washing broken fracturing fluid out of the propped fracture and restores the relative permeability to gas in the invaded matrix of the fracture face. However, recovery of fracturing fluids from the invaded matrix requires overcoming both capillary pressure-driven imbibition and the capillary exit pressure that occurs at the fracture boundary between the matrix and propped fracture. Surface active materials, such as alcohols and surfactants, are often used to reduce the surface tension, and hence the capillary pressure functions in the matrix. These materials are expected to enhance recovery of the fracturing fluid from the matrix, improving load recoveries. Modeling this process with classical reservoir simulators is not possible because they do not allow for the impact of surface tension reduction on capillary pressure functions. A previously reported simulator for modeling fracturing fluid movement has been modified to accommodate the impact of surface tension reduction on capillary pressure. This simulator uses the simultaneous solution (SS) method for solving the two-phase flow equations, followed by calculation of the movement of chemicals based on the pressure solution at each time step. A new modification to the SS method has been developed to allow proper modeling of the impact of capillary pressure reduction by surfactants.Surfactants can reduce capillary pressure in the matrix by reducing surface tension and/or by changing the wettability of the rock surface when they adsorb on a surface. The classical SS method does not maintain proper "mass balance" when surfactants are allowed to change the capillary pressure; the reason for which is demonstrated in this work. The new modification allows surfactants to impact capillary pressure through surface tension reduction and wettability changes.IntroductionSurfactants have many well-known uses in stimulation treatments, including emulsion prevention, wettability alteration, and surface tension reduction. Some surfactants are considered effective for enhancing load recovery of fracturing treatments while some surface active materials, such as methanol, are also considered useful for repairing water blocks. It is generally understood that these materials impact fluid movement and fluid saturations by affecting capillary pressure and relative permeabilities. Recent experimental work has been conducted to quantify the effects of surface wettability changes by certain chemicals on relative permeabilities1 and the role of methanol by evaporation.2 While this work can be evaluated and modeled in the context of classical reservoir simulations,3 the impact of surface wettability changes and surface tension reduction on capillary pressure cannot be modeled with typical simulators.Capillary pressure in reservoirs with permeabilities above 1 md is usually relatively minor (only a few psi) and can often be ignored. As the permeability falls to the microdarcy range, however, the capillary pressure of water in a gas reservoir can easily be several hundred psi. Invading water can, therefore, experience pressure gradients that the gas phase does not experience since gas is the non-wetting phase. Reducing the surface tension is expected to also reduce the capillary pressure. Reducing the capillary pressure is often simply expected to reduce the capillary exit pressure, which is sometimes called the "capillary end effect." However, this terminology ignores the fact that there is a very strong capillary suction into the deeper matrix. As such, reducing the surface tension, and hence the capillary pressure function, can conceptually increase the rate of imbibition and make it more difficult to remove water from the matrix. Resolving this tug-of-war can be difficult in the absence of numerical modeling. Keywords: flow in porous media, concentration, SS method, surfactant, hydraulic fracturing, Simulation, surface tension reduction, Fluid Dynamics, water saturation, reduction Subjects: Hydraulic Fracturing, Reservoir Fluid Dynamics, Flow in porous media This content is only available via PDF. 2007. Society of Petroleum Engineers You can access this article if you purchase or spend a download.