Effectiveness Of Hydraulic Fracturing Research Articles

Hydraulic Fracturing Effect on Flow Resistance in Gas Drainage Hole Area in Coal

Hydraulic Fracturing Effect on Flow Resistance in Gas Drainage Hole Area in Coal

Complex Resistivity Dispersion Characteristics of Water‐Bearing Coal Based on Double Cole‐Cole Model

Reservoir fracture evaluation is an important research topic in the coalfield. In recent years, complex resistivity (CR) has been widely used in oil logging and achieved good results, such as permeability evaluation, water saturation (Sw) prediction, and aquifer identification. Therefore, the method has the potential to evaluate coal seam fracture. In the experiment, the real part R and imaginary part X of bituminous and anthracite coal with different Sw were measured by the impedance measuring instrument, then the Double Cole-Cole model was used to fit experimental data and analyze conductive mechanism. The main results are as follows: (1) the dispersion of CR parameters Reρ and Imρ is closely related to the metamorphism degree, frequency, and Sw; (2) induced polarization is the fundamental reason for the variation of coal samples’ complex resistivity parameters with frequency change; and (3) the Double Cole-Cole model agrees well with the experimental data, and the model parameters m1 and τ2 are strongly correlated with Sw. The parameters m1 and τ2 can be used to evaluate the Sw of fractures in coal seams and thus to evaluate the effect of hydraulic fracturing.

Dual diagnostic method for fracture morphology of thermal coalbed methane reservoir

In most thermal coalbed methane production practices, the average single well production is low and the economic benefit is low. In order to improve the production of thermal coalbed methane, this paper presents a dual diagnosis method for fracture morphology of thermal coalbed methane reservoir to improve hydraulic fracturing effect. The study is carried out as follows: firstly, improved log-log curve method to adapt to coal seam fracturing construction, secondly, establish the inclined stress calculation model of coal seam to obtain the critical depth value, and finally, combine the improved log-log method and critical depth method to form a dual diagnosis approach. Take Baiyang River in Xinjiang as an example, obtain the traffic, rock mechanics and other parameters suitable for the Baiyang River block, the fracture morphology is verified by fracturing data. The experimental results show that the approach can diagnose fracture morphology accurately. <br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/TSCI191209454E">10.2298/TSCI191209454E</a><u></b></font>

Analysis of the tempo‐spatial effects of hydraulic fracturing by drilling through underground coal mine strata on desorption characteristics

AbstractTo elucidate the tempo‐spatial effect and the corresponding mechanism of hydraulic fracturing on gas desorption, the experiments of the hydraulic fracturing in the field and the gas adsorption‐desorption in the laboratory were carried out, respectively. The difference of the effects on the total amount of gas desorption, desorption proportion, moisture content, and in situ gas drainage concentration of the original and fracturing coal samples were studied. The results show that coal moisture increase in the 29 m area of hydraulic fracturing, the greater moisture content and the smaller amount of gas desorption, and the 9 m coal samples moisture content is 2.77 times greater than that of the original coal samples, and whose total amount of gas desorption for 29.8% of the original coal samples. In addition, the closer to the fracturing borehole, the smaller the desorption velocity, which is the fastest in the initial 5 minutes. The desorption velocity of the original coal samples is 5.6 times greater than that of the 9 m coal samples. The desorption proportion of the coal samples is high in early stages, η30 min is 64% (ηi is the proportion of the instantaneous total of gas desorption to the total gas desorption, %), and for η6 h‐12 h is 10%. The tempo‐spatial effects of desorption characteristics can be expressed as the time‐delay effect and a space‐reduction effect. Furthermore, the upper limit of deformation of the coal seam is 3.3‰ and the ability of gas desorption in coal seam significantly decreases. The time of gas drainage concentration exhibits more than 30% increases from the 10 days in the nonfracturing area to 90 days in the fracturing area. Finally, hydraulic fracturing crushes coal, replaces absorption gas, increases the moisture content of coal, reduces various stresses, makes coal shrink, and ultimately achieves the effects of pressure relief and permeability improvement.

Could the Mesoproterozoic Kyalla Formation Emerge as a Viable Gas Condensate Source Rock Reservor Play in the Beetaloo Sub-Basin?

Reservoir and geomechanical analysis of Kyalla Formation core and wireline logs acquired at Beetaloo W-1 indicate the presence of two potential Source Rock Reservoir (SRR) intervals; the middle Kyalla SRR and the lower Kyalla SRR. The key properties of the SRRs include TOC 1-3%wt, PHUT 5-10%BV, SWT 30-60%PV, free gas porosity 2-5%BV, and 20-40scf/ton adsorbed gas content. A Poissons Ratio of 0.15-0.2 and Young’s Modulus of 30-35GPa suggest favourable geomechanical properties for effective hydraulic fracture stimulation. The lower Kyalla SRR has the greatest potential as it displays consistently positive geomechanical properties over the entire SRR interval as well as consistently high free gas porosity (>2-3%BV). Mudgas and core analysis indicate that the reservoir hydrocarbon phase is likely to be a wet gas. Potential retrograde condensation may yield significant condensate and LPG fractions from the produced gas stream.The positive reservoir and geomechanical properties within the Kyalla Formation SRR intervals at Beetaloo W-1 suggest further appraisal work is warranted to determine the deliverability of the SRRs and to determine what LPG and Condensate yields can be recovered at the well head.

Laboratory Investigation of the Effect of Injection Rate on Hydraulic Fracturing Performance in Artificial Transversely Laminated Rock Using 3D Laser Scanning

Among many factors that affect the hydraulic fracturing responses, the injection rate is identified as the first critical factor to be considered by many researchers. However, the internal mechanism of injection rate on the morphology of fracturing surface and gas productivity are still not well understood. In scaled laboratory experiments, artificial interlayered model blocks were produced, according to the development characteristics of silty laminae in continental shale, China, to investigate the effect of injection rate on hydraulic fracturing effectiveness. Macroscopic failure morphology descriptions combined with mesoscopic 3-D laser scanning techniques are both used to reveal the internal influence mechanism of injection rate. Results show that hydraulic fracturing effectiveness improves with the increase of injection rate, by enhancing the total contact area of fracture system, and increasing micro-fractures in the fracture surface. The experimental result first reveals the influential mechanism of injection rate on hydraulic fracturing performance.

Transient-Rate Analysis of Stress-Sensitive Hydraulic Fractures: Considering the Geomechanical Effect in Anisotropic Shale

Summary Production from multistage-fractured horizontal wells (MFHWs) in shale reservoirs causes stress changes that further influence the conductivities of hydraulic fractures. Moreover, many shale rocks are strongly anisotropic. The objective of this study is to semianalytically model hydrocarbon-flow dynamics in reservoirs with MFHWs. The effects of stress-sensitive hydraulic fractures and shale anisotropy are considered. First, this study explores the relationship between principal-stress and pore-pressure changes in anisotropic shale. Second, an exponential correlation is further incorporated to describe the fracture conductivities vs. pore-pressure changes in anisotropic shale. The exponential correlation is validated by matching experimental data of fracture conductivities vs. effective stress. The fracture compressibility df in the exponential equation is stress-dependent rather than constant. Next, this study discretizes each hydraulic fracture into several source segments. For each segment in each timestep, pressure distribution is calculated with source/sink functions. Both the stress field and the hydraulic-fracture conductivities are updated according to the pressure distribution with the previously mentioned correlations before starting the next timestep. In addition to the constant-bottomhole-flowing-pressure condition, nonconstant bottomhole pressure (BHP) in real-field cases can also be entered for this semianalytical model. The model is validated by comparing its results with numerical simulations. A series of type curves q vs. t is generated on the basis of model calculations. The type curves are applied to investigate the effects of initial fracture conductivity Fci, initial fracture compressibility dfi, declining rate of fracture compressibility β, shale anisotropy, and the BHP profiles on MFHW transient-rate behavior. To maximize the hydrocarbon production, the BHP profile must be adjusted on the basis of fracture stress-sensitive characteristics. The semianalytical model is used to analyze two field cases with different pwf profiles under the influence of stress-sensitive hydraulic fractures.

Experimental study on characteristics of water containing coal complex resistivity dispersion

In recent years, there have been great advances in the evaluation of complex resistivity method for rock permeability.Using a complex resistivity method, as a potential non-contact detection method, it is feasible to forecast the permeability of coal seam and evaluate the effect of hydraulic fracturing. In this paper, measurement and numerical simulation are both carried out based on electrical properties of rock. For this purpose, the authors attempted to measure real and imaginary parts of the complex resistivity of two kinds of metamorphic coal in different values of water saturation (Sw) under normal temperature and pressure conditions. The achieved experimental results are presented as follows: (1) The influence of polarization on the complex resistance is very important, which is the cause of frequency dispersion; (2) Regarding real and imaginary parts of the complex resistivity of coal's dispersion characteristics, the real part always gradually decreases with the increase of frequency, while the imaginary part is changed, and the curve has obvious extreme point; (3) the amplitude of real and imaginary parts gradually decrease with increase of Sw; (4) The curve of imaginary part is two segments(only peak), the Cole-Cole model is applicable, while curve is three segments (trough-peak), the double Cole-Cole model is applicable. The results show that the effect of medium polarizability on coal complex resistivity cannot be ignored, indicating that complex resistivity method possesses a great capability in terms of development of coalbed methane and coal mining.

Analyzing the Well-Interference Phenomenon in the Eagle Ford Shale/Austin Chalk Production System With a Comprehensive Compositional Reservoir Model

SummaryWell interference is a common phenomenon in unconventional-reservoir development. The completion and production of infill wells can lead to either positive or negative well-interference impacts on the existing producers. Many researchers have investigated the well-interference phenomenon; however, few of them attempted to apply rigorous simulation methods to analyze both positive and negative well-interference effects, especially in two different formations. In this work, we develop a comprehensive compositional reservoir model to study the well-interference phenomena in the Eagle Ford Shale/Austin Chalk production system. The reservoir model considers capillary pressure in the vapor/liquid-equilibrium (VLE) equation (nanopore-confinement effect), and applies the embedded discrete-fracture model (EDFM) for dynamic fracture modeling. We also include a multisegment-well model to characterize the wellbore-crossflow effect introduced by fracture hits. The simulation results indicate that negative well-interference impact is much more common in the production system. With a smaller permeability difference, the hydraulic-fracturing effect can lead to a positive well-interference period of several hundred days. The nanopore-confinement effect in the Eagle Ford Shale can contribute to the negative well-interference effect. We also analyze the impact of other factors such as initial reservoir pressure, matrix porosity, initial water saturation, and the natural-fracture system on the well performance. Our work provides valuable insights into dynamic well performance under the impact of well interference.

Experimental study on physical simulation of shale gas hydraulic fracturing

Physical simulation of hydraulic fracturing based on the feature of shale gas reservoir is an effective means to comprehend fracture geometry and extension mechanism, which is also one of the most effective methods for shale gas reservoir reconstruction. Take hydraulic fracturing construction as reference and select critical factor for object, shale gas hydraulic fracturing experimental system was designed. The system consists of true triaxial module, hydraulic servo pump module and acoustic emission module. By setting up different parameters of fracturing in simulation experiment, the influence of parameter factors on hydraulic fracturing effect is studied. The results show that type and quantity of perforation, size and direction of in-situ stress, fracturing fluid displacement and other parameters have different influence on the fracturing effect. This experiment provides a certain theoretical basis for shale gas hydraulic fracturing technology in construction site.

Anti-channeling cementing technology for long horizontal sections of shale gas wells

Large-scale hydraulic fracturing combined with horizontal well drilling is the key technology in shale gas development. But poor cementing quality is a crucial bottleneck restricting well completion and reservoir stimulation. In this paper, the shale gas development blocks in the Sichuan Basin were taken as the examples to explore the process and support measures that can be used to keep the mechanical integrity of cement sheath under the effect of hydraulic fracturing. It is indicated that the near-bit three-centralizer drifting BHA used for casing stiffness simulation can decrease the casing running difficulty in the long horizontal section of a shale gas well and increase the time efficiency and safety of casing running; that the flushing efficiency of high-efficiency oil flushing spacer fluid system is higher than 90% from room temperature to 120 °C, so it can guarantee the displacement efficiency of cement slurry to the oil-based drilling fluid and the effective cementing of borehole wall; that the performance of anti-channeling ductile cement slurry used in the cementing of long horizontal sections in this area after it is set is confirmed, with the elastic modulus of set cement being lower than 7 GPa and triaxial strength being higher than 40 MPa, so as to alleviate or avoid the damage to cement sheath in the process of fracturing; and that cementing quality is improved by applying the support technologies, e.g. drilling fluid adjustment, pre-stress cementing and ground high-pressure pumping. During 2015–2016, these cementing technologies were applied in 85 wells in the Sichuan Basin. The average well depth of these wells is 4832 m, the average length of horizontal sections is 1560 m and the quality rate of well cementing is 89.58%. During the waiting-on-cement (WOC) time after well cementing, there is no sustained casing pressure. And gas channeling in the annulus during well drilling, completion and test is improved remarkably. It is concluded that this suite of technologies can guarantee and improve the cementing quality of long horizontal sections in shale gas wells and provides good cementing conditions for shale gas development.

Effects of mechanical layering on hydraulic fracturing in shale gas reservoirs based on numerical models

Generally, induced hydraulic fractures are generated by fluid overpressure and are used to increase reservoir permeability through forming interconnected fracture systems. However, in heterogeneous and anisotropic rocks, many hydraulic fractures may become arrested or offset at layer contacts under certain conditions and do not form vertically connected fracture networks. Mechanical layering is an important factor causing anisotropy in sedimentary layers. Hence, in this study, with a shale gas reservoir case study in the Longmaxi Formation in the southeastern Chongqing region, Sichuan Basin, we present results from several numerical models to gain quantitative insights into the effects of mechanical layering on hydraulic fracturing. Results showed that the fractured area caused by hydraulic fracturing indicated a linear relationship with the neighboring layer’s Young’s modulus. An increase of the neighboring layer’s Young’s modulus resulted in better hydraulic fracturing effects. In addition, the contact between two neighboring layers is regarded as a zone with thickness and mechanical properties, which also influences the effects of hydraulic fracturing in reservoirs. The initial hydraulic fracture was unable to propagate into neighboring layers under a relatively low contact’s Young’s modulus. When associated local tensile stresses exceeded the rock strength, hydraulic fractures propagated into neighboring layers. Moreover, with the contact’s Young’s modulus becoming higher, the fractured area increased rapidly first, then slowly and finally became stable.

High-Volume Hydraulic Fracturing and Human Health Outcomes: A Scoping Review.

Examine extent of peer-reviewed literature exploring human health effects of hydraulic fracturing (HVHF). A scoping review methodology was used to examine peer-reviewed studies published from 2000 through 2017 that empirically examine direct health impacts of hydraulic fracturing. Through September 2017, only 18 studies were found published in peer-reviewed journals that met our requirements for inclusion in the review. Most of these studies resulted in positive or mixed findings of health outcomes. The paucity of studies reflects the difficulty in drawing direct connections between HVHF and human health outcomes. Many health outcomes may take years to emerge, exposure often occurs in lightly populated rural areas with older, poorer, and sicker residents, and diagnosis is difficult without physician knowledge of prior exposure. Primary care providers should record thorough histories to help guide future treatment.

Study on the Influence of Bedding Density on Hydraulic Fracturing in Shale

Natural fractures and weak bedding planes are important for forming complex fracture networks in shale reservoirs. There are many sets of shale layers with different bedding densities in Sichuan, China. In this paper, three typical drilling cores with different bedding densities were collected. The shale rock mechanical properties and fracture morphology are investigated. Bedding density affects the strength and deformation characteristics. A fracture characterization model is proposed, and the hydraulic fracturing effects are evaluated. It is shown that with decreasing bedding density, the peak strength and elastic modulus increase, and Poisson’s ratio decreases gradually. The effect of natural fractures on hydraulic fracturing is investigated by analyzing the expansion of hydraulic fracture. The research shows that natural fractures have a significantly induced effect on the initiation and propagation of hydraulic fracture. According to the results of physical simulation of hydraulic fracturing, three types fracture extension models are established: a strong extended complex fracture model, a weak bedding extended complex fracture model, and a natural fracture crack propagation model. Natural fractures with different bedding structural properties may result in different propagation types of hydraulic fracture.

The effects of combined-cycle generation and hydraulic fracturing on the price for coal, oil, and natural gas: Implications for carbon taxes

We identify how the increased efficiency of generating electricity using gas-fired combined-cycle technology and the increased production of natural gas due to hydraulic fracturing in the US affect the first purchase price for coal, oil, and natural gas and their prices at electricity generating plants by estimating a cointegrating vector autoregression model from monthly observations between January 1991 and February 2016. Simulation experiments indicate that combined-cycle generation raises the long-run price of natural gas, both at the wellhead and electricity generating plants. Conversely, the increased production of natural gas has a relatively small long-run effect on natural gas prices. Historical counterfactuals indicate increased natural gas production since June 2003 lowers natural gas prices by an average of $0.16 per million BTU while combined cycle generation increases prices by an average of $0.54 per million BTU since April 1999. This increase is captured by natural gas producers such that the margin between prices at electricity generating plants and the wellhead shrinks by about $0.05 per million BTU. This analysis suggests that market relations among energy prices and their statistical ordering will reinforce the direct effects of a carbon tax on relative prices in ways that enhance interfuel substitution towards natural gas.

Optimization and Evaluation of Multiple Hydraulically Fractured Parameters in Random Naturally Fractured Model Blocks: An Experimental Investigation

Researchers have recently realized that the non-tectonic natural fractures are developed in shale formations and significant for the exploitation of shale gas. Studies have shown that the tectonic fractures in naturally fractured reservoirs have influences on the maximization of stimulated reservoir volume (SRV) during hydraulic fracturing. However, the effect of the non-tectonic randomly natural fractures on the fracturing network propagation is not well understood. Laboratory experiments are proposed to study the evolution of fracturing network in naturally fractured formations with specimens that contain non-tectonic random fractures. The influences of the dominating factors were studied and analyzed, with an emphasis on natural fracture density, stress ratio, and injection rate. The response surface methodology was employed to perform the multiple-factor analysis and optimization in the maximization of the SRV. A sensitivity study reveals a number of interesting observations resulting from these parameters on the fracturing network evaluation. It is suggested from the geometry morphology of fracturing network that high natural fracture density and injection rate tend to maximize the fracturing network. The influence of stress contrast on fracturing network is nonlinear; an optimal value exists resulting in the best hydraulic fracturing effectiveness.

Determination of solvation free energy of carbon dioxide (CO2) in the mixture of brine, Alfa Olefin Sulfonate (AOS) and CH4 after foam fracturing in the shale reservoirs on enhanced shale gas recovery (ESGR)

Fracturing in the form of foam fracturing is often involved in dealing with the exploitation of unconventional shale resources. On the other hand, Molecular Dynamics (MD) simulation has been developed progressively in the recent decades to provide the temporal and the spatial resolutions, which are experimentally unavailable. The MD simulation considers the atomic and the molecular interactions at microscopic and macroscopic levels. The objective of this research is to improve fluid interaction during hydraulic fracturing of the shale gas reservoirs. The potential parameters include the high reservoir pressure and high temperature (HPHT), the concentration of the surfactant, the presence of carbon dioxide (CO2), and the brine salinity. The simulation focuses on the post effect of hydraulic fracturing on the shale system after the fracturing process has had taken place whereby the CO2 is introduced into the shale gas system, which consists of methane (CH4) with brine and surfactants applied during the foam fracturing is Alfa Olefin Sulfonate (AOS). Different brine salinity, temperature, and pressure are varied in the simulation to determine the most spontaneous combination for the reservoir condition for the solvation of CO2 in the shale fluid system in the reflection of solvation free energy. The simulation result is validated with the experimental study, which is performed to determine the critical micelle concentration (CMC) value of AOS solution in the two-phase fluid consisting of CO2 and brine. The result shows that the most spontaneous system happens at the condition of 423.15 K and 30,000 ppm salinity. The pressure is fairly insignificant to the output of solvation free energy. The larger the negativity of the solvation free energy indicates that the more spontaneous of the CO2 in the interaction with the surrounding particles in the system. This research is beneficial in the future prediction of the behavior and the spontaneity of the CO2 in the shale gas recovery. Apart from that, the CMC in simulation and experimental results are 0.014 wt% and 0.016 wt% which proves that the simulation result is valid.

Experimental study of directional propagation of hydraulic fracture guided by multi-radial slim holes

The conventional hydraulic fracturing fails in the target oil/gas zone (remaining oil, closed reservoir, etc.) which is not located in the azimuth of maximum horizontal stress of available wellbores. The technology of directional propagation of hydraulic fracture guided by vertical multi-radial slim holes is innovatively developed. In order to verify this technology, lots of true triaxial hydraulic fracturing simulation experiments were carried out with artificial cores, aiming at investigating the influence of in-situ stress, fracturing fluid displacement, and azimuth, diameter, number, and spacing of radial slim holes on fracture propagation. The results show that directional propagation of hydraulic fractures guided by vertical multi-radial slim holes is feasible. Regardless of varied radial slim hole and in-situ stress parameters, hydraulic fracture always initiates in the heel of radial slim hole. For hydraulic fracturing assisted by single radial slim hole, smaller horizontal stress difference (3 MPa, σH/σh = 1.25) and smaller radial slim hole azimuth (15°) may guide propagation of hydraulic fractures along radial slim hole, and larger horizontal stress difference (6 MPa, σH/σh = 1.67) can sharply reduce guidance of radial slim hole. Affected by mutual interference from guidance of radial slim holes and controlling of horizontal in-situ stress, fractures tend to distort along fracture length and fracture height. For hydraulic fracturing assisted by vertical multi-radial slim holes, horizontal stress difference is one of key factors influencing the directional propagation effect of hydraulic fracture. Larger horizontal in-situ stress difference (>6 MPa, σH/σh > 1.67) hardly results in directional propagation of hydraulic fracture along radial slim hole row, and creates bigger diversion angle of fracture, and larger azimuth (>45°) of radial slim hole row reduces the guidance strength, resulting small fracture diversion radius. In conditions of larger angle between target zone and maximum horizontal stress, and requirement of large azimuth of radial slim hole row, the effective hydraulic fracture propagation along radial slim holes and ideal fracture height will be achieved through human intervention, e.g. increment of the number and diameter of radial slim holes, reduction of radial slim holes spacing, increment of fracturing fluid displacement, etc. The simulation results provide methods for designing directional propagation of hydraulic fractures guided by vertical multi-radial slim holes.

EFFICIENCY ANALYSIS OF HYDRAULIC FRACTURING IN KISLORSKOE OIL FIELD

Background The paper presents an analysis of the efficiency of geological and technical measures performed in the wells of the Kislorskoe oil field. Aims and Objectives Conduct an analysis of the effectiveness of hydraulic fracturing in the Kislorskoe field, assess the operational characteristics of the wells after the fracturing. Results It was established that the geological and technological measures such as sidetracking with a horizontal termination, the hydraulic fracturing of the formation, perforation of non-perforated layers of strata, the repair and insulation works had a positive impact on the development of oil reserves at the facility. The main reasons for the insignificant effect are the high water cut of the production (due to the breakthrough of the bottom water) and the low filtration and reservoir properties of the formation in the interval of hydraulic fracturing.

Разработка вероятностно-статистических моделей для оценки эффективности применения пропантного гидравлического разрыва пласта (на примере объекта Тл-Бб Батырбайского месторождения)

Разработка вероятностно-статистических моделей для оценки эффективности применения пропантного гидравлического разрыва пласта (на примере объекта Тл-Бб Батырбайского месторождения)