Showing papers by "Ripudaman Manchanda published in 2020"

Integrating Reservoir Geomechanics with Multiple Fracture Propagation and Proppant Placement

Abstract: This paper presents the formulation and results from a coupled finite-volume (FV)/finite-area (FA) model for simulating the propagation of multiple hydraulically driven fractures in two and three dimensions at the wellbore and pad scale. The proposed method captures realistic representations of local heterogeneities, layering, fracture turning, poroelasticity, interactions with other fractures, and proppant transport. We account for competitive fluid and proppant distribution between multiple fractures from the wellbore. Details of the model formulation and its efficient numerical implementation are provided, along with numerical studies comparing the model with both analytical solutions and field results. The results demonstrate the effectiveness of the proposed method for the comprehensive modeling of hydraulically driven fractures in three dimensions at a pad scale.

Integrated Analysis of Tracer and Pressure-Interference Tests To Identify Well Interference

Abstract: In ultralow-permeability reservoirs, communication between wells through connected fractures can be observed through tracer and pressure-interference tests. Understanding the connectivity between fractured horizontal wells in a multiwell pad is important for infill well drilling and parent-child well interactions. Interwell tracer and pressure-interference tests involve two or more fractured horizontal wells and provide information about hydraulic-fracture connectivity between the wells. In this work, we present an integrated approach based on the analysis of tracer and pressure interference data to obtain the degree of interference between fractured horizontal wells in a multiwell pad. We analyze well interference using tracer (chemical tracer and radioactive proppant tracer) and pressure data in an 11-well pad in the Permian Basin. Changes in pressure and tracer concentration in the monitor wells were used to identify and evaluate interference between the source and monitor wells. Extremely low tracer recovery and weak pressure response signify the absence of connected fractures and suggest that interference through matrix alone is insignificant. Combined tracer and pressure-interference data suggest connected fracture pathways between the communicating wells. The degree of interference can be estimated in terms of pressure response times and tracer recovery. An effective reservoir model was used to simulate pressure interference between wells during production. Simulation results indicate that well interference observed during production is primarily because of hydraulically connected fractures. Combined tracer and pressure-interference analysis provides a unique tool for understanding the time-dependent connectivity between communicating wells, which can be useful for optimizing infill well drilling, well spacing, and fracture sizing in future treatment designs.

Preloading Depleted Parent Wells To Avoid Fracture Hits: Some Important Design Considerations

Abstract: Mitigating the negative impact of fracture hits on production from parent and child wells is challenging. This work shows the impact of parent-well depletion and repressurization on child-well fracture propagation and parent-well productivity. The goal of this study is to develop a method to better manage production/injection in the parent well so that the performance of the child well can be improved by minimizing fracture interference and fracture hits. A fully integrated equation-of-state compositional hydraulic fracturing and reservoir simulator has been developed to seamlessly model fluid production/injection (water or gas) in the parent well and model propagation of multiple fractures from the child well. The effects of drawdown rate and production time is presented for a typical shale play for three different fluid types: black oil, volatile oil, and dry gas. The results show that different reservoir fluids and drawdown strategies for the parent wells result in different stress distributions in the depleted zone, and this affects fracture propagation in the child well. Different strategies were studied to repressurize the parent well by varying the injected fluids (gas vs. water), the volumes of the preload fluid, and so on. It was found that fracture hits can be avoided if the fluid injection strategy is designed appropriately. In some poorly designed preloading strategies, fracture hits are still observed. Last, the impact of preloading on the parent-well productivity was analyzed. When water was used for preloading, water blocking was observed in the reservoir, and it caused damage to the parent well. However, when gas was injected for preloading, the oil recovery from the parent well was observed to increase. Such simulations of parent–child well interactions provide much-needed quantification to predict and mitigate the damage caused by depletion, fracture interference, and fracture hits.

A New Mechanism for the Formation of Hydraulic Fracture Swarms

Abstract: Mine-back experiments, lab experiments, and cores taken through fractured rock show that hydraulic fracturing treatments can create swarms of fractures. Subcritical crack growth, microcracking ahead of the fracture tip and failure of weak planes in the rock are mechanisms that have helped explain fracture swarming observed in both natural and hydraulic fractures. In this work, we show that fracture swarms can also form in homogeneous rocks by complex stress fields induced in the reservoir by propagating hydraulic fractures or by other geologic events. A 3-D fracturing simulator based on the Displacement Discontinuity Method (DDM) and a 3-D fracturing-reservoir simulator based on the Finite Volume Method (FVM) were used to simulate hydraulic fracture propagation. These models can accurately account for stress shadow effects and simulate fracture turning during propagation with the direction of propagation calculated using the maximum tangential stress criterion. Simultaneous propagation of multiple fractures is simulated to exhibit multi-stranded fracture propagation behavior in the absence of natural fractures in the reservoir. Additionally, we assess the impact of natural fractures in the reservoir on the created fracture swarms. The stress shadow around a single fracture is spatially variable. Simulation of the propagation of multiple fractures shows that parts of the fractures propagating in lower stress contrast regions turn more readily than the parts of the fractures propagating in higher stress contrast regions. The smaller width of the fracture in the high-stress layers induces a smaller stress shadow while the larger width of the fracture surface in the low-stress layers induces a larger stress shadow. Higher stress interference in certain layers causes fracture turning in those layers and induces splitting of the fracture tip resulting in swarms of fractures. The FVM simulations clearly show this effect. Fracture branching and tip splitting are only evident when these simulations are run in 3-D. The fracture branching results obtained from the simulators show good agreement with field core-through observations from the Eagle Ford and the Permian basins. This work shows that the stress field created by propagating fractures can result in the creation of fracture swarms. It is shown that this branching can happen in the absence of material flaws and weaknesses. This new mechanism of fracture branching to create fracture swarms is quantified through both DDM and finite volume simulations.

DFIT Analysis and Interpretation in Layered Rocks

Abstract: Diagnostic fracture injection tests (DFITs) are often used to estimate formation properties such as closure stress, pore pressure, and matrix permeability. These estimations are typically based on analysis of pressure data assuming the closure of simple planar fractures in homogeneous reservoirs. These interpretations are incorrect when dealing with complex reservoir environments such as layered reservoirs with different properties and stresses. This paper investigates the impact of such complex environments on DFIT interpretation and presents a systematic method to analyze the data. A 3-D implicitly integrated poroelastic fracture-reservoir-wellbore model is used to simulate DFITs. DFIT fracture propagation and well shut-in are simulated with implicitly computed fluid leak-off and fracture closure. The model is validated by simulating a DFIT for a homogeneous reservoir and the implicitly calculated surface pressure is interpreted to obtain the simulation inputs (stress, pore pressure, permeability, etc.). A multi-layer reservoir model is then built in the numerical simulation domain and a DFIT is simulated in the target layer. The properties and thickness of the layers are varied to analyze their impact on the observed DFIT signature. We analyze the impact of layer thicknesses, layer stresses, pressure and permeability of each layer, stress contrast between the layers, fracture interaction with bedding planes and the rock roughness and hardness of each layer on the DFIT pressure signature. We show that the layer property variations can cause different but characteristic DFIT pressure responses. Fracture propagation into layers with different stresses induces multiple closure events in the observed pressure signature, which provides a quantitative representation of the fracture height growth. The emergence of these closure events in the pressure signature are found to be dependent on the hardness and modulus of the rock layers and the fluid communication between the closing parts of the fracture. The DFIT signature patterns are also found to correlate with the interaction of the fracture with bedding planes (cross/arrest/divert) and provide valuable insights into fracture containment. In this work we present best practices for performing DFIT analysis in layered reservoirs. Results from simulated DFITs in layered reservoirs clearly show the effect of key heterogeneity parameters on DFIT responses. The results from this work can be used to more accurately determine reservoir closure stress, pore pressure, reservoir permeability, fracture compliance, fracture conductivity, and fracture containment in heterogeneous reservoirs.

Multi-Well Poroelastic Pressure Interference Analysis: Towards Real-Time Fracture Diagnostics

Abstract: Traditionally, time-consuming, numerical simulations are used to calculate and interpret poroelastic pressure changes induced by hydraulic fractures. In this work, we develop and apply semi-analytical models to calculate the poroelastic pressure signature and estimate the geometry of the propagating fracture. The speed of the analytical forward model allows us to apply inverse models (which require the forward model to be run hundreds of times) to compute the fracture geometry in near-real-time. A 3-D, semi-analytical model is developed to calculate reservoir deformation, stress shadow, and pressure changes around multiple hydraulic fractures. The model is extended and combined with an inversion algorithm to calculate the geometry of the propagating fracture for a measured poroelastic pressure signature recorded in a monitoring well. The model is then applied to a real field scenario with a treatment well and a fractured monitoring well where the pressure signature measured in the monitoring wells is used to estimate the dimensions of the propagating fractures in several fracturing stages. The analytical model presented here is shown to be very accurate for predicting the stress shadow of multiple propagating fractures. This model is used to quantify the impact of various operational unknowns on the poroelastic pressure signature. We consider scenarios where the pressure change in the monitoring well is measured through isolated fractures in the monitoring well. We demonstrate the impact of the number of propagating fractures, their length, height, net pressure, and the monitoring well fracture geometry on the observed pressure change. Based on this understanding, an inversion algorithm is developed to convert the recorded poroelastic pressure into the dimensions of the propagating fractures and the dimensions of the monitoring fractures. Finally, the method is used to interpret poroelastic pressure measurements recorded in a pair of wells in the Delaware basin to estimate fracture dimensions. In this work, we showcase the development and application of a novel semi-analytical model to interpret poroelastic pressure signatures observed in isolated monitoring well fractures. The application of the new method to estimate fracture dimensions is shown using a newly developed inversion algorithm. The efficient computations provide clear evidence that the developed workflow can be used for near-real-time fracture diagnostics.

Fracture Sequencing in Multi-Well Pads: Impact of Staggering and Lagging Stages in Zipper Fracturing on Well Productivity

Abstract: Zipper fracturing is a method of sequencing frac jobs in multi-well pads that helps increase operational efficiency and reduce stimulation time for a pad. This technique involves stimulating several wells in a pad in a prescribed sequence of stages. In this work, we provide a thorough assessment of the various factors impacting the effectiveness of zipper fracturing treatments and provide a methodology for selecting an optimum sequence of fracture stages. A fully implicit, parallelized, 3-D, pad-scale reservoir-fracturing simulator is used to simulate the dynamic propagation of multiple, non-planar fractures from multiple treatment wells while capturing the stress interference between fractures. This interference is captured both on an intra-well as well as an inter-well scale. Interaction between fractures propagating from different wells is found to be dependent on pad design, completion design, and reservoir parameters. We evaluate the effectiveness of the stimulation operation by comparing the impact of operation decisions on the created fracture geometries and simulated productivity of the propagated fractures using seamless fracturing-reservoir simulations. The simulation results are used to understand the impact of well spacing, stage spacing, staggering of zipper-frac wells, lagging of stages during zipper fracturing, size of the frac job, stress contrast in the reservoir and rock properties. Using multi-cluster fracturing simulations and accurate proppant distribution calculations in the wellbore, we consider the impact of various operational decisions mentioned above on the distribution of proppant in the created fractures. We observe that fracture closure during shut-in of a stage impacts the created fracture geometries. This affects the proppant distribution in the fractured stages. The impact of the operational decisions on the fracture conductivity degradation during stimulation is also captured using seamless fracture-reservoir simulations. We show that the results obtained from these simulations can help design pad-scale operations to maximize the fracture-reservoir contact area or improve the productivity of the wells. In this work, for the first time, we assess the impact of zipper fracturing on well productivity by performing coupled fracturing-reservoir simulations. The software is used to simulate fracture propagation and fracture closure during shut-in and production. The results obtained from these simulations recommend an optimized fracture sequencing, stage lag and staggering strategy to maximize the productivity of the pad.