Pressure-Transient Behavior of Vertical Wells Considering Dynamic Water Hammer and Dynamic Induced Fracture: Theory and Case Studies

Water injection can result in thecreation of inducedfractureby connecting natural fractures. The induced fracture penetrates theentire reservoir, leading to the interconnection of injection andproduction wells and ultimately resulting in water breakthrough andthe abandonment of production wells. During well work, the inducedfracture exhibits dynamic behavior characterized by extension andclosure, known as the dynamic-induced fracture phenomena. During theshut-in process, fracture closure phenomena are often accompaniedby water hammer phenomena, which can be detected bottom hole pressuredata. However, numerical simulation methods are difficult to describetheir dynamic processes. Therefore, we urgently need a mathematicalmodel to fill this gap. In this work, we developed a waterflooding-induceddynamic fracture (WIDF) model. Dynamic water hammer phenomena, multi-dynamicclosure phenomena, and fracture storage phenomena are introduced intothe WIDF model to describe the induced fracture dynamic behavior.Field cases demonstrate that the WIDF model can improve the accuracyof interpreted parameters and correct incorrect model selection. Greenfunction and Newman product method are used to characterize single-phasewater flows within tight reservoirs. Then, the induced fracture isdiscrete into N segments through the boundary elementmethod. Discrete-induced fractures are divided into n parts. Basedon the induced fracture bending property, conductivity variation isindependent in each part. The feature line method is used to solvethe pressure response of the dynamic water hammer. The Duhamel principleis applied to couple the storage effects and reservoir pressure response.The Laplace transform method transforms the model into Laplace spaceso that it can be solved easily, and the Stehfest numerical inversionmethod transforms the model into real space to obtain the final solution.Our results show that the dynamic water hammer flow (DWH) regime withan oscillation curve and the multi-dynamic closure flow (MDCF) regimewith peaks exist on the type curve. Resistance coefficient (f) and inertia coefficient (I) controlthe DWH regime. Fracture storage coefficient (C f), dynamic fracture closure rates (Delpat m), and induced fracture closure half-lengths (x dfm) control the MDCF regime. It is worth notingthat the peak position can be adjusted by the Delpat m and x dfm parameters, achievinga more accurate match to the field cases. The C f is identified, which corrected for the amplified wellborestorage coefficient. Obtained permeability is also in a reasonablerange of permeability for tight reservoirs. In summary, a series ofmathematical methods are used to develop and solve an injection wellmodel to identify the dynamic behavior of the induced fracture. Numericalsimulation methods are used to verify the accuracy of the WIDF model.Two field cases from X Oilfield demonstrate the practicability ofthe WIDF model. Dynamic identification of the induced fracture wouldhelp engineers develop appropriate injection schemes to prevent waterbreakthroughs.

Automated summary

Water injection can lead to the creation of induced fractures, resulting in the interconnection of injection and production wells and water breakthrough. The development of a waterflooding-induced dynamic fracture model helps describe the dynamic behavior of induced fractures and is important for preventing water breakthroughs.