Towards Field Testing of the Flowback Technology for Multistage-Fractured Horizontal Wells: Modeling-Based Design and Practical Implications
Authors: Osiptsov Anderei , Vainshtein Albert , Boronin Sergei , Faizullin Ildar , Paderin Grigory , Shurunov Andrei , Uchuev Ruslan , Garagash Igor , Tolmacheva Kristina , Lezhnev Konstantin , Prunov Dmitry , Chebykin Nikolay 
Published: October 2019

Abstract
Selection of an optimum scenario of well flowback and startup after multistage fracturing and the design of the field experiment are based on mathematical modeling of filtration in a propped fracture, taking into account the compaction of a proppant pack, embedment of proppant into the fracture faces, tensile failure of the fracture walls and proppant flowback. For this purpose, we have proposed a simulation-based process for the development of a series of field trials for the well flowback after multistage fracturing. There are two different scenarios of flowback regime (smooth and aggressive) with a step-wise increase in the diameter of the choke to determine the upper and lower limits of the safe operating envelope of the well flowback. Based on the results of a series of parametric calculations, the preferred ranges of implementation of the flowback technology are formulated in terms of the steps of change and the duration of the periods of constant diameter of the choke, which are planned to be tested in the field. Several horizontal wells with hydraulic fracturing at the terrigenous field of Western Siberia will be planned to study the impact of inflow dynamics on the pipeline. To test the research hypotheses, two limiting scenarios of the flowback were proposed in terms of the dynamics of the opening of the choke with time: "smooth" and "aggressive" (the well is flowing without assistance, before the installation of the ESP). In addition to monitoring the parameters of well production (flow rate, water cut, bottom hole and wellhead pressure), suspension samples will be taken to analyze the particulate content, according to a pre-approved schedule for the purpose of granulometric analysis of the solid phase. The results of parametric numerical calculations, based on our in-house hydrodynamic and geomechanical models, allowed us to determine the critical values of drawdown, in which undesirable geomechanical phenomena are realized (primarily proppant flowback, proppant embedment into the fracture walls and compression of the proppant pack under the action of closure stresses and associated reduction in the width of the propped fracture, as well as the risk of rock failure). Parametric model-based studies suggest a hypothesis for testing in the field that the accumulated production after hydraulic fracturing depends on the dynamics of flowback and well startup. To select candidate wells, we use the results of solving the inverse problem to determine the governing parameters of the formation, in which undesirable geomechanical effects are most pronounced, as well as to take into account the requirements for the representativeness and repeatability of field tests. On the basis of the field data, a decision tree will be formed to maximize the efficiency of the experiment and operational supervision. The authors are aware of the scale of uncertainties associated with the interpretation of data obtained as a result of field experiments. The demand from the operator to improve the methodology of hydraulic fracturing in the region allows us to analyze the current methods of conducting flowback operations. Conducting field tests is possible without significant capital expenditures, since it does not require additional equipment on test wells. We proposed a simulation-based process for the development of a series of field trials on flowback.