Abstract
Polymer gels used in hydraulic fracturing to generate fracture geometry and ensure proppant transport are also known to damage the proppant pack permeability, and this damage reduces the well production rate. As reuse of produced water and other highly saline water sources for fracturing applications grows, there is further damage expected from scale/precipitate deposition into the proppant pack. Past studies in the literature focus on impairment of proppant pack permeability from broken polymer gel residue, but precipitation of scale from source water is not considered. The objectives of this study are (i) to develop laboratory methods of assessing conductivity reduction from different fluid-based factors such as polymer residue and scale and (ii) to develop correlations to predict retained permeability based on simplified measurements. The simple methods will minimize the need for the standard conductivity testing, which can be time consuming, expensive, prone to significant test-to-test variation, and still subject to experimental artifacts. By the use of simplified procedures, the cost of conductivity testing can be reduced while allowing validation of the simplified method results.
We demonstrate a simple benchtop method to measure permeability of a proppant pack damaged by polymer residue, scale, or both. This method provides an opportunity to study a specific damage source in isolation, where the test is not influenced by problems such as spatial inhomogeneity of gel break, ineffective cleanup of filter cake, creation of proppant crush fines, etc., that are inherent in conventional API-type conductivity tests.
Experimental measurements of retained permeability arising from different sources such as polymer residue and scale were compared with traditional conductivity measurements. They were also correlated with empirical permeability models that rely on proppant pack porosity.
One key insight from the new, simplified method for proppant damage assessment is that the loss of permeability correlates with porosity reduction from polymer residue volume with a similar extension to scale precipitation.
