Matrix treatments of openhole horizontal wells are extremely difficult. Placement of the treatment fluids at the very places where necessary, i.e. where damage exists, calls for diversion techniques of superior performance, due to the length of the section to be treated. Failure in achieving high diverting efficiency results in either incomplete damage removal and/or requirements for uneconomical volumes of treatment fluids.

Suspensions of particulate diverting agents build up very efficient cakes, however are costly due to the huge depositing surface. Therefore, the preferred diverting technique consists in pumping viscous banks into sections of high fluid intake. These banks are made of either non-Newtonian gels or foams having downhole qualities in the 60 to 85% range.

The aim of the present paper is to provide modeling equations for the radial placement of viscous pills around openhole horizontal wells. Primary porosity reservoir rocks are considered (usually 50- to 5,000-mD permeability sandstones) as well as naturally fractured ones (mostly carbonates). The pills are made of gels of Power-law fluid mechanics behavior. The increasing apparent viscosity of the gel with increasing distance to the well (due to decreasing shear rate) is taken into account.

Fluid bank pseudoskin equations are derived and used to optimize the diverting process. Optimization is either achieved by the selection of the proper characteristics of the viscous pill (e.g. n’ and K’ coefficients of a Power-law fluid) or by the pill volume and injection rate at which the latter is squeezed into the reservoir rock. Quantitative guidelines are provided with the aim of minimizing the cost of the diverting process as well as the duration of the matrix treatment.

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