Analysis of Transparent Gelatin as a Reservoir Analogue for Hydraulic Fracturing Laboratory Experiments

Abstract

ABSTRACT: Gelatin was often used as a reservoir analogue material to model hydraulic fracturing in brittle, hydrocarbon-filled rock formations, with its transparency allowing direct, visual observation of the fracture growth. Nevertheless, not many studies elaborate on the scalability of laboratory experiments where gelatin was used in comparison to actual field-scale hydraulic fracture treatments. Model laws from the literature derived to relate lab-scale physical models displaying hydraulic fracture growth to the prototype parameters are used to assess the representation of elastic deformation, crack formation energy, treatment time, and confining stress environment, honoring the governing laws of fluid-driven fracture propagation in linearly elastic media. In this work, the lab-scale parameters of an experimental study on gelatin blocks of 7-to-8%-by-weight concentration are assessed against typical slickwater and crosslinked gel fracture treatment parameters from the Barnett Shale as part of a dimensional scaling evaluation. The analysis shows the gelatin reservoir analogue scaling better against crosslinked gel compared to slickwater field operations, with the laboratory conditions accentuating Mode I fracture toughness over viscous fluid effects, compared to the field. Subsequently, a set of laboratory parameters is proposed at a higher gelatin concentration (18-to-19%-by-weight), yielding improved scalability against field operations, minimizing the difference between the lab-scale and the corresponding field-scale values of each dimensionless group, within the constraints of the available laboratory equipment. Finally, the implications of the absence of leakoff in experiments on gelatin specimens is discussed and comparisons are made between gelatin and other transparent lab-scale reservoir analogues. 1. INTRODUCTION Analogue experimental work is –bar none– a fundamental branch of scientific method. Selecting the appropriate analogue material, which satisfies a set of criteria determining whether a candidate analogue material can be considered a laboratory version of the natural counterpart is one of the biggest challenges when developing an experimental study. This paper elaborates on the scalability of transparent gelatin as a reservoir analogue in hydraulic fracturing block experiments.