Proppant Flowback: Can We Mitigate the Risk?

Abstract

We propose a new model and workflow to predict, quantify and mitigate undesired flowback of proppant from created hydraulic fractures. We demonstrate several field cases in which we predict significant proppant flowback and propose options for mitigation. Mitigation of proppant flowback is based on case- specific changes in the fracturing treatment design and modifications in the well startup schedule that preserve near-wellbore conductivity. The presented workflow integrates four key components of proppant flowback study: (A) simulation of the fracturing job with a high-resolution model of proppant placement inside a fracture; (B) subsequent simulation of flowback from the created fractures equipped by a validated proppant flowback model; (C) a series of laboratory experiments, which quantify the proppant flowback for a wide range of commercial proppants; and (D) an accurate mathematical model, which is validated by the results of laboratory experiments and integrated into a flowback simulator to predict the behavior of injected proppant. Each component is presented with sufficient details to demonstrate its necessity for accurate modeling of a coupled solid-and-fluid flow inside a fracture. The presented theory of proppant pack mobilization is based on the concept of a proppant pack erosion process evolving from free boundaries of proppant packs. The theory confirms that proppant flowback critically depends on flow rate, proppant, fracture, and reservoir parameters. Laboratory experiments on proppant flowback in a cell support these theoretical predictions. The theoretical model of proppant flowback is integrated into the numerical simulator of early-time production from a fractured reservoir and predicts flowback of both injected solids and fluids from a fracture. We show that the combination of the proppant flowback model, laboratory experiments, hydraulic fracturing design tool, and early-time production simulator result in a useful workflow for prediction and mitigation of issues with proppant flowback and production decline. The entire workflow was validated using field cases where proppant flowback was observed. Modeled amounts of flowed back proppant are in good agreement with amounts of proppant observed in the field. Hydraulic fracturing design optimization was performed to minimize or eliminate proppant flowback. The novelty of the proposed study is related to the model of proppant flowback, which accounts for erosion of the proppant pack and is calibrated against unique laboratory experiments. The presented model and proppant flowback mitigation workflow can assist in understanding and mitigating proppant flowback events that can occur during wide range of oilfield operations.

Experimental Study on the Backflow Mechanism of Proppants in Induced Fractures and Fiber Sand Control Under the Condition of Large-Scale and Fully Measurable Flow Field

“…Figure 17 shows the shape of the sand bank before and after flowback with different fiber lengths. The calculated CRs under different fiber lengths (3,6, and 12 mm) are 0.38, 0.34, and 0.29, respectively, which indicate that the proppant pack becomes more resistant to fluid action with the increase of fiber length.…”

“…Related studies have shown that the average gas production decline rate of proppant backflow gas wells is more than 3 times that of normal production wells. 3 In addition, the accumulation of backflow proppants at the bottom of the well buries the gas layer or causes erosion of surface pipelines when it is discharged from the wellhead, and so on, which poses safety hazards in construction and production. 4,5 Therefore, the study of proppant backflow is of great significance for the development and production of gas wells.…”

Application of accelerated fixed-point algorithms to hydrodynamic well-fracture coupling

“…The numerical model of a hydraulic fracture [17] is the key component of the simulator and incorporates both hydrodynamical and geomechanical aspects of the problem. Fluid flow relative to the proppant pack inside the fracture is governed by the Darcy law.…”

Cascading Failure Phenomenon in the Multi-Stage Hydraulically Fractured Wells

“…We were 425 prescribing different critical velocity or, equivalently, different critical flow rate for each fracture in the range from 3.3 bbl/day to 87.0 bbl/day. In the numerical model, we coupled the model of the transient flows in a well, described in [22], with the numer-430 ical models of individual fractures [23]. Each fracture was represented by a grid of conductive cells with fixed width simulating a porous medium.…”

“…The well and fracture models were coupled using iterative algorithm based on Picard iterations (or fixed point itera-440 tions method) [25] that ensured balance of pressures and flow rates between them within certain tolerance. More detailed description of the numerical model and its application to simulation of the cascading failure problem can be found in [23,26]. The problem of pressure-rate coupling 445 between well and fractures has been closely investigated in [27], including study of accuracy and influence of different modifications of algorithm on convergence of fixed point iterations.…”