Optimization of hydraulic fracturing design under spatially variable shale fracability

空间可变页岩可压裂性条件下的水力压裂设计优化

Journal of Petroleum Science and Engineering, Volume 138, February 2016, Pages 174-188

Atefeh Jahandideh, Behnam Jafarpour

Abstract:Current hydraulic fracturing designs are based on equal fracture intervals (spacing) along horizontal wells. Typical fracture spacing ranges from 50 to 600 feet while the fracture half-lengths normally vary between 100 and 600 feet. Symmetric spacing designs assume homogeneous shale mechanical property distributions, e.g. rock brittleness or fracability, which may not be the case in many shale plays. Fracability of the shale rock is an important property that controls the efficiency of the fracturing process. Therefore, the heterogeneity in shale fracability can have an important impact on the design and optimization of the hydraulic fracturing process. In particular, the optimal number, location, and length of the fractures can depend on rock fracability distribution. In this paper, we develop an optimization approach for hydraulic fracturing design under geospatial variability in shale fracability and investigate several aspects of the proposed fracture design optimization approach. In particular, we optimize the hydraulic fracturing design by implementing a variant of the Simultaneous Perturbation Stochastic Approximation algorithm to maximize the net present value of the shale asset, including the cost of fracturing and the revenue from gas production. The optimization framework provides a systematic design approach for hydraulic fracturing of unconventional reservoirs and can be applied to improve production efficiency and reduce the cost and environmental impact of hydraulic fracturing. We demonstrate the effectiveness and suitability of the proposed method using a series of numerical experiments in shale gas development.

Mechanisms of imbibition during hydraulic fracturing in shale formations

页岩储层水力压裂过程中的渗吸机理

Journal of Petroleum Science and Engineering, Volume 141, May 2016, Pages 125-132

Z. Zhou, H. Abass, X. Li, D. Bearinger, W. Frank

Abstract:Hydraulic fracturing technology has been proven to significantly increase production from shale gas and oil formations. However, during a hydraulic fracturing treatment a large percentage of the fracturing fluid usually remains unrecovered. Therefore, the reasons for this low fracturing fluid recovery have become the focus of many studies. Imbibition of fracturing fluid in the shale is believed to be one of the explanations for the low amount of the fracture fluid recovery. The fluid is imbibed by the shale matrix and trapped inside the rock. Capillarity has generally been the primary mechanism considered during imbibition in conventional formations, such as sandstone and carbonate formations. In shale formations osmosis diffusion also exists and cannot be ignored because the clay in the shale rock functions similarly to that of a membrane. It is believed that both capillarity and osmosis diffusion work together to result in imbibition during hydraulic fracturing in shale formations. This paper investigates the effects of both capillarity and osmosis diffusion as the key mechanisms in fluid imbibition through simultaneous imbibition experiments. The results of these tests illustrate that the imbibition process is dominated by both capillarity and osmosis diffusion. This domination is based on the change of water saturation in shale rocks. In addition, the capillary and osmotic pressures, which influence the imbibed rate, can be qualitatively determined by the contact angle and salinity, respectively. Higher capillary and osmotic pressures correlate to faster rates of imbibition.This study, which examines the mechanisms of imbibition and their influences, can improve the understanding of fluid behavior when imbibition occurs during hydraulic fracturing in shale formations. The understanding of this behavior is useful for further simulation research.

Adsorption of hydraulic fracturing fluid components 2-butoxyethanol and furfural onto granular activated carbon and shale rock

水力压裂液成分乙二醇单丁醚和糠醛对颗粒活性炭和页岩石的吸附

Chemosphere, Volume 164, December 2016, Pages 585-592

Katherine E. Manz, Gregory Haerr, Jessica Lucchesi, Kimberly E. Carter

Abstract:The objective of this study was to understand the adsorption ability of a surfactant and a non-surfactant chemical additive used in hydraulic fracturing onto shale and GAC. Experiments were performed at varying temperatures and sodium chloride concentrations to establish these impacts on the adsorption of the furfural (a non-surfactant) and 2-Butoxyethanol (2-BE) (a surfactant). Experiments were carried out in continuously mixed batch experiments with Langmuir and Freundlich isotherm modeling. The results of the experiments showed that adsorption of these compounds onto shale does not occur, which may allow these compounds to return to the surface in flowback and produced waters. The adsorption potential for these chemicals onto GAC follows the assumptions of the Langmuir model more strongly than those of the Freundlich model. The results show uptake of furfural and 2-BE occurs within 23 h in the presence of DI water, 0.1 mol L−1 sodium chloride, and in lab synthesized hydraulic fracturing brine. Based on the data, 83% of the furfural and 62% of the 2-BE was adsorbed using GAC.

Smart magnetic markers use in hydraulic fracturing

智能磁钉在水力压裂中的应用

Chemosphere, Volume 162, November 2016, Pages 23-30

Jarosław Zawadzki, Jan Bogacki

Abstract:One of the main challenges and unknowns during shale gas exploration is to assess the range and efficiency of hydraulic fracturing. It is also essential to assess the distribution of proppant, which keeps the fracture pathways open. Solving these problems may considerably increase the efficiency of the shale gas extraction. Because of that, the idea of smart magnetic marker, which can be detected when added to fracturing fluid, has been considered for a long time. This study provides overview of the possibilities of magnetic marker application for shale gas extraction. The imaging methods using electromagnetic markers, are considered or developed in two directions. The first possibility is the markers' electromagnetic activity throughout the whole volume of the fracturing fluid. Thus, it can be assumed that the whole fracturing fluid is the marker. Among these type of hydraulic fracturing solutions, ferrofluid could be considered. The second possibility is marker, which is just one of many components of the fracturing fluid. In this case feedstock magnetic materials, ferrites and nanomaterials could be considered. Magnetic properties of magnetite could be too low and ferrofluids' or nanomaterials' price is unacceptably high. Because of that, ferrites, especially ZnMn ferrites seems to be the best material for magnetic marker. Because of the numerous applications in electronics, it is cheap and easily available, although the price is higher, then that of magnetite. The disadvantage of using ferrite, could be too small mechanical strength. It creates an essential need for combining magnetic marker with proppant into magnetic-ceramic composite.

A review of the issues and treatment options for wastewater from shale gas extraction by hydraulic fracturing

页岩气开采水力压裂所产生的废水问题及应对策略

Fuel, Volume 182, 15 October 2016, Pages 292-303

José M. Estrada, Rao Bhamidimarri

Abstract:Since the beginning of this millennium, shale gas extraction by horizontal drilling and hydraulic fracturing has boosted U.S. gas production, changing the global energy markets and leading to low natural gas and oil prices. Following the expansion of this industry, other countries such as U.K., Poland or China are exploring and supporting its extraction as a way to secure energy independence in an increasingly unstable geopolitical context and as an effective transition substitute for coal while moving towards a renewable energy market. However, there are important environmental concerns associated to shale gas production including atmospheric pollution and air quality issues, risks of water pollution and nuisance to the population caused by road traffic and noise. Water management is one of the most challenging problems since hydraulic fracturing requires millions of liters of water and produces high volumes of liquid effluents at variable compositions and rates. The present review focuses on the characteristics of this wastewater and the options existing to minimize its environmental impacts. At the moment, deep well injection and re-use are the most commonly employed strategies for this wastewater in the U.S. but the stricter regulations in other regions will require further treatment. Partial treatment and reuse is the preferred option where feasible. Otherwise, techniques such as mechanical vapor compression, thermal distillation or forward osmosis may be needed in order to meet the requirements for discharge.

Coupled 3-D numerical simulation of proppant distribution and hydraulic fracturing performance optimization in Marcellus shale reservoirs

Marcellus页岩储层支撑剂分布及水力压裂性能优化耦合三维数值模拟

International Journal of Coal Geology, Volumes 147–148, 1 August 2015, Pages 35-45

B. Kong, E. Fathi, S. Ameri

Abstract:Effective hydraulic fracturing stimulation is highly reliant on the flow area and proppant pack permeability of the induced hydraulic fractures. The flow area is largely determined by proppant distribution while fracture permeability is mainly governed by proppant sizes. To create a fracture with a large flow area, small proppants are essential to maintain a minimum proppant settling velocity; on the other hand, large proppant sizes provide higher proppant pack permeability. Therefore, an optimum operational procedure, i.e., scheduling of injection rate, proppant size and volume, is required to achieve maximum well productivity index. This, however, requires both field experiments (e.g., small volume pre-job tests) and an advanced numerical simulator that couples solid and fluid transport with fracture propagation model including mass exchange between reservoir matrix and hydraulic fracture, i.e., leak-off rate.

In this study, we focused on developing new modules for our in-house 3-D numerical simulator where proppant transport and reservoir performance optimization is considered. In new module Navier–Stokes equation describing fluid flow in the fracture and leak-off in the formation is coupled with mass conservation equation governing the proppant transport, and solved using finite difference approach. Fracture propagation is also one-way coupled with proppant transport and fluid flow using in-house 3D hydraulic fracturing simulator “HFWVU”. During the simulation Proppant slippage velocity is considered over wide range of hydraulic fracturing propagation regimes, i.e., toughness-dominated to viscosity-dominated cases, with small and large leak-offs.

The simulation results predict that reservoir matrix permeability highly impacts the proppant size selection and pumping scheduling to achieve the optimum reservoir stimulation performance. Ignoring the fluid–solid interaction, i.e., proppant settling velocity, in hydraulic fracturing simulation leads to overestimating the efficiency of the process in wide range of operation conditions. It has also been predicted that the optimum combination of proppant size and their volume portion exists for specific reservoir and treatment conditions that can optimize fracture performance.

Uncertainty analysis of the reservoir behavior using experimental design technique shows that hydraulic fracturing efficiency on production performance can be highly influenced by reservoir matrix permeability, i.e., uncontrollable variable. This implies that the same hydraulic fracturing procedure applied in conventional reservoirs might not be as efficient in unconventional reservoir and special attention to reservoir characteristics needs to be made while designing the hydraulic fracturing procedure. Followed by reservoir matrix permeability, proppant volume and relative proppant/fluid density have the highest impact on hydraulic fracturing efficiency. This study couples hydraulic fracturing simulation with reservoir simulation and is a unique approach for the further understanding of proppant transport and settling, fracture geometry variation and fracture production performance. It also provides foundation for the development of sound numerical models for hydraulic fracturing design.