Modeling Performance of Horizontal Wells with Multiple Fractures in Tight Gas Reservoirs PDF Download
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Author: Guangwei Dong Publisher: ISBN: Category : Languages : en Pages :
Book Description
Multiple transverse fracturing along a horizontal well is a relatively new technology that is designed to increase well productivity by increasing the contact between the reservoir and the wellbore. For multiple transverse fractures, the performance of the well system is determined by three aspects: the inflow from the reservoir to the fracture, the flow from the fracture to the wellbore, and the inflow from the reservoir to the horizontal wellbore. These three aspects influence each other and combined, influence the wellbore outflow. In this study, we develop a model to effectively formulate the inter-relationships of a multi-fracture system. This model includes a reservoir model and a wellbore model. The reservoir model is established to calculate both independent and inter-fracture productivity index to quantify the contribution from all fractures on pressure drop of each fracture, by using the source functions to solve the single-phase gas reservoir flow model. The wellbore model is used to calculate the pressure distribution along the wellbore and the relationship of pressure between neighboring fractures, based on the basic pressure drop model derived from the mechanical energy balance. A set of equations with exactly the same number of fractures will be formed to model the system by integrating the two models. Because the equations are nonlinear, iteration method is used to solve them. With our integrated reservoir and wellbore model, we conduct a field study to find the best strategy to develop the field by hydraulic fracturing. The influence of reservoir size, horizontal and vertical permeability, well placement, and fracture orientation, type (longitudinal and transverse), number and distribution are completely examined in this study. For any specific field, a rigorous step-by-step procedure is proposed to optimize the field.
Author: Guangwei Dong Publisher: ISBN: Category : Languages : en Pages :
Book Description
Multiple transverse fracturing along a horizontal well is a relatively new technology that is designed to increase well productivity by increasing the contact between the reservoir and the wellbore. For multiple transverse fractures, the performance of the well system is determined by three aspects: the inflow from the reservoir to the fracture, the flow from the fracture to the wellbore, and the inflow from the reservoir to the horizontal wellbore. These three aspects influence each other and combined, influence the wellbore outflow. In this study, we develop a model to effectively formulate the inter-relationships of a multi-fracture system. This model includes a reservoir model and a wellbore model. The reservoir model is established to calculate both independent and inter-fracture productivity index to quantify the contribution from all fractures on pressure drop of each fracture, by using the source functions to solve the single-phase gas reservoir flow model. The wellbore model is used to calculate the pressure distribution along the wellbore and the relationship of pressure between neighboring fractures, based on the basic pressure drop model derived from the mechanical energy balance. A set of equations with exactly the same number of fractures will be formed to model the system by integrating the two models. Because the equations are nonlinear, iteration method is used to solve them. With our integrated reservoir and wellbore model, we conduct a field study to find the best strategy to develop the field by hydraulic fracturing. The influence of reservoir size, horizontal and vertical permeability, well placement, and fracture orientation, type (longitudinal and transverse), number and distribution are completely examined in this study. For any specific field, a rigorous step-by-step procedure is proposed to optimize the field.
Author: Jiajing Lin Publisher: ISBN: Category : Languages : en Pages :
Book Description
Horizontal wells have been used to increase reservoir recovery, especially in unconventional reservoirs, and hydraulic fracturing has been applied to further extend the contact with the reservoir to increase the efficiency of development. In the past, many models, analytical or numerical, were developed to describe the flow behavior in horizontal wells with fractures. Source solution is one of the analytical/semi-analytical approaches. To solve fractured well problems, source methods were advanced from point sources to volumetric source, and pressure change inside fractures was considered in the volumetric source method. This study aims at developing a method that can predict horizontal well performance and the model can also be applied to horizontal wells with multiple fractures in complex natural fracture networks. The method solves the problem by superposing a series of slab sources under transient or pseudosteady-state flow conditions. The principle of the method comprises the calculation of semi-analytical response of a rectilinear reservoir with closed outer boundaries. A statistically assigned fracture network is used in the study to represent natural fractures based on the spacing between fractures and fracture geometry. The multiple dominating hydraulic fractures are then added to the natural fracture system to build the physical model of the problem. Each of the hydraulic fractures is connected to the horizontal wellbore, and the natural fractures are connected to the hydraulic fractures through the network description. Each fracture, natural or hydraulically induced, is treated as a series of slab sources. The analytical solution of superposed slab sources provides the base of the approach, and the overall flow from each fracture and the effect between the fractures are modeled by applying superposition principle to all of the fractures. It is assumed that hydraulic fractures are the main fractures that connect with the wellbore and the natural fractures are branching fractures which only connect with the main fractures. The fluid inside of the branch fractures flows into the main fractures, and the fluid of the main fracture from both the reservoir and the branch fractures flows to the wellbore. Predicting well performance in a complex fracture network system is extremely challenged. The statistical nature of natural fracture networks changes the flow characteristic from that of a single linear fracture. Simply using the single fracture model for individual fracture, and then adding the flow from each fracture for the network could introduce significant error. This study provides a semi-analytical approach to estimate well performance in a complex fracture network system.
Author: Olufemi Morounfopefoluwa Olorode Publisher: ISBN: Category : Languages : en Pages :
Book Description
Various models featuring horizontal wells with multiple induced fractures have been proposed to characterize flow behavior over time in tight gas and shale gas systems. Currently, there is little consensus regarding the effects of non-ideal fracture geometries and coupled primary-secondary fracture interactions on reservoir performance in these unconventional gas reservoirs. This thesis provides a grid construction tool to generate high-resolution unstructured meshes using Voronoi grids, which provides the flexibility required to accurately represent complex geologic domains and fractures in three dimensions. Using these Voronoi grids, the interaction between propped hydraulic fractures and secondary "stress-release" fractures were evaluated. Additionally, various primary fracture configurations were examined, where the fractures may be non-planar or non-orthogonal. For this study, a numerical model was developed to assess the potential performance of tight gas and shale gas reservoirs. These simulations utilized up to a half-million grid-blocks and consider a period of up to 3,000 years in some cases. The aim is to provide very high-definition reference numerical solutions that will exhibit virtually all flow regimes we can expect in these unconventional gas reservoirs. The simulation results are analyzed to identify production signatures and flow regimes using diagnostic plots, and these interpretations are confirmed using pressure maps where useful. The coupled primary-secondary fracture systems with the largest fracture surface areas are shown to give the highest production in the traditional "linear flow" regime (which occurs for very high conductivity vertical fracture cases). The non-ideal hydraulic fracture geometries are shown to yield progressively lower production as the angularity of these fractures increases. Hence, to design optimum fracture completions, we should endeavor to keep the fractures as orthogonal to the horizontal well as possible. This work expands the current understanding of flow behavior in fractured tight-gas and shale-gas systems and may be used to optimize fracture and completion design, to validate analytical models and to facilitate more accurate reserves estimation.
Author: Jie Zeng Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Current analytical models for multi-fractured horizontal wells (MFHW) generally neglect reservoir heterogeneity, typical seepage characters of unconventional reservoir, partially penetrating fracture and various fracture damage mechanisms. In this thesis, three linear flow models have been developed to facilitate pressure and rate behavior analysis of shale, tight sand and unconventional reservoir with damaged fractures. These models are validated by comparing with KAPPA Ecrin and are more accurate than previous linear flow models in modeling partially penetrating cases. Field data are analyzed and results prove the reliability of these models. The first model is for heterogeneous shale reservoir with multiple gas transport mechanisms. It subdivides the reservoir into seven parts, namely, two upper/lower regions, two outer regions, two inner regions, and hydraulic fracture region. Fracture interference is simulated by locating a no-flow boundary between two adjacent fractures. The locations of these boundaries are determined based on the boundary's pressure to satisfy the no-flow assumption. Adsorption/desorption, gas slippage and diffusion effects are included for rigorous modeling of flow in shale. Sensitivity analysis results suggest that larger desorption coefficient causes smaller pressure and its derivative as a larger proportion of gas is desorbed in formation and contributes to productivity. The influences of other parameters, such as matrix II permeability, matrix block size, secondary fracture permeability, hydraulic fracture conductivity, and fracture pattern are also discussed. The second model is for heterogeneous tight sand reservoir with threshold pressure gradient (TPG). The linear flow sub-regions are the same as those of the first model. TPG and pressure drop within the horizontal wellbore are included. Simulation results suggest that TPG affects middle-late time behaviors. Greater TPG results in higher pressure drop and accelerates production decline. But this influence is marginal when TPG is small. Effects of other parameters, such as formation permeability, fracture length, conductivity, and wellbore storage are also investigated. The third model is for heterogeneous reservoir with various fracture damage. In this model, the following possible fracture damage situations are discussed: (1) choked fracture damage (2) partially propped fracture, (3) fracturing fluid leak-off damage, (4) dual or multiple damage effects. Simulation results indicate that choked frature damage influences early-mid time performance. Partially propped section within fracture dominates formation linear flow regime. Only severe matrix impairment near fracture face can have noticeable effects on pressure and rate response. A new parameter, skin factor ratio, is applied to describe the relative magnitude of multiple damage mechanisms. Reservoir heterogeneity and fracture damage make the pressure and rate behaviors deviate significantly from undamaged one but one can distinguish major damage mechanisms even in heterogeneous reservoir.
Author: Roberto Aguilera Publisher: PennWell Books ISBN: Category : Science Languages : en Pages : 730
Book Description
This book deals exclusively with naturally fractured reservoirs and includes many subjects usually treated in separate volumes. A highly practical edition, Naturally Fractured Reservoirs is written for students, reservoir geologists, log analysts and petroleum engineers.
Author: Francis Nzubechukwu Nwabia Publisher: ISBN: Category : Hydraulic fracturing Languages : en Pages : 0
Book Description
Hydraulically fractured horizontal wells are widely adopted for the development of tight or shale gas reservoirs. The presence of highly heterogeneous, multi-scale, fracture systems often renders any detailed characterization of the fracture properties challenging. The discrete fracture network (DFN) model offers a viable alternative for explicit representation of multiple fractures in the domain, where the comprising fracture properties are defined in accordance with specific probability distributions. However, even with the successful modelling of a DFN, the relationship between a set of fracture parameters and the corresponding production performance is highly nonlinear, implying that a robust history-matching workflow capable of updating the pertinent DFN model parameters is required for calibrating stochastic reservoir models to both geologic and dynamic production data. This thesis will develop an integrated approach for the history matching of hydraulically fractured reservoirs. First, multiple realizations of the DFN model are constructed with conditioning data based on available geological information such as seismic data, well logs, and rate transient analysis (RTA) interpretations, which are useful for inferring the prior probability distributions of relevant fracture parameters. A pilot point scheme and sequential indicator simulation are employed to update the distributions of fracture intensities which represent the abundance of secondary fractures (NFs) in the entire reservoir volume. Next, the model realizations are upscaled into an equivalent continuum dual-porosity dual-permeability model and subjected to numerical multiphase flow simulation. The predicted production performance is compared with the actual recorded responses. Finally, the DFN-model parameters are adjusted following an indicator-based probability perturbation method. Although the probability perturbation technique has been applied to update facies distributions in the past, its application in modeling DFN distributions is limited. An indicator formulation is proposed to account for the non-Gaussian nature of the DFN parameters. The algorithm aims at minimizing the objective function while reducing the uncertainties in the unknown fracture parameters. The novel probabilistic-based framework is applied to estimate the posterior probability distributions of transmissivity of the primary fracture (Tpf), transmissivity of the secondary induced fracture (Tsf) and secondary fracture intensity (Psf32L), secondary fracture aperture (re), length and height (L and H), in a multifractured shale gas well in the Horn River Basin. An initial realization of the DFN model is sampled from the prior probability distributions using the Monte Carlo simulation. These probability distributions are updated to match the production history, and multiple realizations of the DFN models are sampled from the updated (posterior) distributions accordingly. The key novelty in the developed probabilistic approach is that it accounts for the highly nonlinear relationships between fracture model parameters and the corresponding flow responses, and it yields an ensemble of DFN realizations calibrated to both static and dynamic data, as well as the related upscaled flow-simulation models. The results demonstrate the utility of the developed approach for estimating secondary fracture parameters, which are not inferable from other static information alone.
Author: Craig Matthew Freeman Publisher: ISBN: Category : Languages : en Pages :
Book Description
Various analytical, semi-analytical, and empirical models have been proposed to characterize rate and pressure behavior as a function of time in tight/shale gas systems featuring a horizontal well with multiple hydraulic fractures. Despite a small number of analytical models and published numerical studies there is currently little consensus regarding the large-scale flow behavior over time in such systems. The purpose of this work is to construct a fit-for-purpose numerical simulator which will account for a variety of production features pertinent to these systems, and to use this model to study the effects of various parameters on flow behavior. Specific features examined in this work include hydraulically fractured horizontal wells, multiple porosity and permeability fields, desorption, and micro-scale flow effects. The theoretical basis of the model is described in Chapter I, along with a validation of the model. We employ the numerical simulator to examine various tight gas and shale gas systems and to illustrate and define the various flow regimes which progressively occur over time. We visualize the flow regimes using both specialized plots of rate and pressure functions, as well as high-resolution maps of pressure distributions. The results of this study are described in Chapter II. We use pressure maps to illustrate the initial linear flow into the hydraulic fractures in a tight gas system, transitioning to compound formation linear flow, and then into elliptical flow. We show that flow behavior is dominated by the fracture configuration due to the extremely low permeability of shale. We also explore the possible effect of microscale flow effects on gas effective permeability and subsequent gas species fractionation. We examine the interaction of sorptive diffusion and Knudsen diffusion. We show that microscale porous media can result in a compositional shift in produced gas concentration without the presence of adsorbed gas. The development and implementation of the micro-flow model is documented in Chapter III. This work expands our understanding of flow behavior in tight gas and shale gas systems, where such an understanding may ultimately be used to estimate reservoir properties and reserves in these types of reservoirs.
Author: Guangwei Dong
Author: Guangwei Dong
Author: Jiajing Lin
Author: Shanshan Yao
Author: Olufemi Morounfopefoluwa Olorode
Author: Jie Zeng
Author: Imad Brohi
Author: Roberto Aguilera
Author: Feng Zhang
Author: Francis Nzubechukwu Nwabia
Author: Craig Matthew Freeman