Production Enhancement by Microproppants: Concept Proof Using Laboratory Experiment and Numerical Modeling

ABSTRACT: In our previous work, an improved fracturing treatment, which combines a mixture of solid delayed acid generating material (SDAGM) with microproppants in the pad/pre-pad fluids during the engineering process, was demonstrated to be an effective technology by a series of laboratory tests and further investigated with mesoscopic fluid dynamics – microscopic solid mechanics coupling simulations. In this work, two field-scale porous media fluid flow models, consisting of rock matrix, randomly distributed microfractures and a major hydraulic fracture, are developed to evaluate the production enhancement of using microproppants for a producing well in an unconventional reservoir. The rock matrix is constructed as porous media with hydraulic properties of tight carbonate formation. The fluid flow in the rock matrix and fractures are mutually communicated. The permeability of zones representing hydraulic fracture and microfractures are determined by upscaling the hydraulic conductivities of fracture and microfractures containing supporting proppants and microproppants. The simulation can predict the well productivity with and without microproppants in the hydraulic fracturing treatment. This developed model can be applied to optimize the concentration of microproppants in the field operation to maximize the well productivity. 1. INTRODUCTION Horizontal drilling and multistage hydraulic fracturing are two critical technologies that make it economically feasible to produce hydrocarbon from unconventional reservoir formations. Horizontal drilling increases the wellbore length exposed to reservoir mass. Hydraulic fracturing enhances production by creating fractures and sustaining their opening using solid particles (called proppants) such that the contact area between producing rock mass and fluid pathways (fractures and well) are significantly increased. Most unconventional formations, such as shales and tight carbonates, contain extensive natural microfractures. Before hydraulic fracturing treatment, these microfractures may be sealed and thus inactive. Hydraulic fracturing will change the stress state around the newly created main fractures, which may reactivate existing natural fractures impacted by the stress change (see Fig. 1). In addition, new microfractures may also be created. Similar to main hydraulic fractures, these microscopic fractures, pre-existing or newly created, will close after the hydraulic fracturing pressure is released. If they can be kept open (e.g., during production), the well productivity can be further enhanced significantly. However, the proppants designed for supporting the main hydraulic fractures cannot enter these microfractures because of their large size relative to the microfracture aperture.