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Author: Mohammed Rashnur Rahman Publisher: ISBN: Category : Hydraulic fracturing Languages : en Pages : 320
Book Description
Previous empirical models of propped fracture conductivity are based either on data sourced from single investigations or on data not in the public domain. In this work, statistically rigorous models of propped fracture conductivity are developed using a database of fracture conductivity experiments reported in technical literature over the last 40 years. The database contains the results from about 2700 experimental runs. Propped fracture conductivity is the dependent variable and proppant types, mesh size, proppant concentration, formation hardness, closure stress, formation temperature, and polymer concentration are the independent variables. The mother database is partitioned into subsets; that is different databases with each daughter database having complete information in relation to the dependent and independent variables. As a result, the number of independent variables included in the daughter databases varied from three to six. Seventy percent of the data was used to develop the models while 30% of the data was used to validate them. First, fixed effect models were developed using regression analysis. Afterwards, three, four and five factor models were compared for two types of proppant: sand and ceramic proppant. The five factor model appeared to be the most prominent one. The analysis was further carried out using five factors of these two types of proppant. Mixed effect modeling was employed because of the disparate sources of the data and also the temporal diversity of the dataset. The mixed effect model appeared to be the better than the fixed effect model while compared the error terms. Also, because the mother database contained some missing values, two statistical imputation approaches were employed to predict the missing values which are categorical imputation and multiple imputation using chained equations. Imputations are employed because it is speculated that a model developed using a large number of data points should provide better predictions. Generally, the mean squared error (MSE) is less in the mixed effect model for sand and in the categorical imputation model for ceramic proppant. But, to be more precise on the performance of the models, model predictions were compared with an existing propped fracture conductivity model and different case histories published in literature. Subsequently, the models of this research can be arranged in order of predictive performance: multiple imputation model, mixed effect model, fixed effect/categorical imputation model. The results also indicate that mesh size, closure stress, formation hardness, and proppant concentration significantly affect fracture conductivity from a statistical point of view. Formation temperature and polymer concentration affect conductivity negatively but they were not statistically significant. Engineers will have access to a propped fracture conductivity database based on experiments reported over the past 40 years in technical literature. Engineers can use the models developed based on this database to generate statistical distributions of propped fracture conductivity for a variety of proppant characteristics and formation conditions. The models presented here are based on data from experimental investigations in different laboratories thereby reducing the bias that may be present in single laboratory investigations.
Author: Mohammed Rashnur Rahman Publisher: ISBN: Category : Hydraulic fracturing Languages : en Pages : 320
Book Description
Previous empirical models of propped fracture conductivity are based either on data sourced from single investigations or on data not in the public domain. In this work, statistically rigorous models of propped fracture conductivity are developed using a database of fracture conductivity experiments reported in technical literature over the last 40 years. The database contains the results from about 2700 experimental runs. Propped fracture conductivity is the dependent variable and proppant types, mesh size, proppant concentration, formation hardness, closure stress, formation temperature, and polymer concentration are the independent variables. The mother database is partitioned into subsets; that is different databases with each daughter database having complete information in relation to the dependent and independent variables. As a result, the number of independent variables included in the daughter databases varied from three to six. Seventy percent of the data was used to develop the models while 30% of the data was used to validate them. First, fixed effect models were developed using regression analysis. Afterwards, three, four and five factor models were compared for two types of proppant: sand and ceramic proppant. The five factor model appeared to be the most prominent one. The analysis was further carried out using five factors of these two types of proppant. Mixed effect modeling was employed because of the disparate sources of the data and also the temporal diversity of the dataset. The mixed effect model appeared to be the better than the fixed effect model while compared the error terms. Also, because the mother database contained some missing values, two statistical imputation approaches were employed to predict the missing values which are categorical imputation and multiple imputation using chained equations. Imputations are employed because it is speculated that a model developed using a large number of data points should provide better predictions. Generally, the mean squared error (MSE) is less in the mixed effect model for sand and in the categorical imputation model for ceramic proppant. But, to be more precise on the performance of the models, model predictions were compared with an existing propped fracture conductivity model and different case histories published in literature. Subsequently, the models of this research can be arranged in order of predictive performance: multiple imputation model, mixed effect model, fixed effect/categorical imputation model. The results also indicate that mesh size, closure stress, formation hardness, and proppant concentration significantly affect fracture conductivity from a statistical point of view. Formation temperature and polymer concentration affect conductivity negatively but they were not statistically significant. Engineers will have access to a propped fracture conductivity database based on experiments reported over the past 40 years in technical literature. Engineers can use the models developed based on this database to generate statistical distributions of propped fracture conductivity for a variety of proppant characteristics and formation conditions. The models presented here are based on data from experimental investigations in different laboratories thereby reducing the bias that may be present in single laboratory investigations.
Author: Kathryn Elizabeth Briggs Publisher: ISBN: Category : Languages : en Pages :
Book Description
Hydraulic fracturing is the primary stimulation method within low permeability reservoirs, in particular shale reservoirs. Hydraulic fracturing provides a means for making shale reservoirs commercially viable by inducing and propping fracture networks allowing gas flow to the wellbore. Without a propping agent, the created fracture channels would close due to the in-situ stress and defeat the purpose of creating induced fractures. The fracture network conductivity is directly related to the well productivity; therefore, the oil and gas industry is currently trying to better understand what impacts fracture conductivity. Shale is a broad term for a fine-grained, detrital rock, composed of silts and clays, which often suggest laminar, fissile structure. This work investigates the difference between two vertical zones in the Fayetteville shale, the FL2 and FL3, by measuring laboratory fracture conductivity along an artificially induced, rough, aligned fracture. Unpropped and low concentration 30/70 mesh proppant experiments were run on samples from both zones. Parameters that were controllable, such as proppant size, concentration and type, were kept consistent between the two zones. In addition to comparing experimental fracture conductivity results, mineral composition, thin sections, and surface roughness scans were evaluated to distinguish differences between the two zones rock properties. To further identify differences between the two zones, 90-day production data was analyzed. The FL2 consistently recorded higher conductivity values than the FL3 at closure stress up to 3,000 psi. The mineral composition analysis of the FL2 and FL3 samples concluded that although the zones had similar clay content, the FL2 contained more quartz and the FL3 contained more carbonate. Additionally, the FL2 samples were less fissile and had larger surface fragments created along the fracture surface; whereas the FL3 samples had flaky, brittle surface fragments. The FL2 had higher conductivity values at closure stresses up to 3,000 psi due to the rearrangement of bulky surface fragments and larger void spaces created when fragments were removed from the fracture surface. The conductivity difference between the zones decreases by 25% when low concentration, 0.03 lb/ft2, 30/70 mesh proppant is placed evenly on the fracture surface. The conductivity difference decrease is less drastic, changing only 7%, when increase the proppant concentration to 0.1 lb/ft2 30/70 mesh proppant. In conclusion, size and brittleness of surface fracture particles significantly impacts the unpropped and low concentration fracture conductivity. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152755
Author: Mark John McGinley Publisher: ISBN: Category : Languages : en Pages :
Book Description
Production of hydrocarbons from low-permeability shale reservoirs has become economically feasible thanks in part to advances in horizontal drilling and hydraulic fracturing. Together, these two techniques help to create a network of highly-permeable fractures, which act as fluid conduits from the reservoir to the wellbore. The efficacy of a fracturing treatment can best be determined through fracture conductivity analysis. Fracture conductivity is defined as the product of fracture permeability and fracture width, and describes both how much and how easily fluid can flow through fractures. It is therefore directly related to well performance. The goal of this work is to explore fracture conductivity of Marcellus shale samples fractured in both horizontal and vertical orientations. The Marcellus shale, located primarily in Pennsylvania, Ohio, West Virginia, New York, and Maryland, is the largest gas-bearing shale formation in North America, and its development has significant implications on regional economies, the northeast United States' energy infrastructure, and the availability of petrochemical plant feedstock. In this work, a series of experiments was conducted to determine the propped fracture conductivity of 23 different samples from Elimsport and Allenwood, Pennsylvania. Before conductivity measurements were taken, the pedigree of samples was verified through XRD analysis, elastic rock properties were measured and compared against literature values, and fracture surface contours were mapped and measured. Fracture conductivity of both horizontally and vertically-fracture samples was determined by measuring the pressure drop of nitrogen gas through a modified API conductivity cell. Results show that fracture conductivity varies as a function of fracture orientation only when anisotropy of the rock's mechanical properties is pronounced. It is hypothesized that the anisotropy of Young's Modulus and Poisson's Ratio play a significant role in fracture mechanics, and therefore in the width of hydraulically-induced fractures. Ultimately, the experiments conducted as part of this work show that fracture conductivity trends are strongly tied to both proppant concentration and the rock's mechanical properties. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155300
Author: Javed Akbar Khan Publisher: ISBN: Category : Electronic books Languages : en Pages : 0
Book Description
Optimum conductivity is essential for hydraulic fracturing due to its significant role in maintaining productivity. Hydraulic fracture networks with required fracture conductivities are decisive for the cost-effective production from unconventional shale reservoirs. Fracture conductivity reduces significantly in shale formations due to the high embedment of proppants. In this research, the mechanical properties of shale samples from Sungai Perlis beds, Terengganu, Malaysia, have been used for computational contact analysis of proppant between fracture surfaces. The finite element code in ANSYS is used to simulate the formation/proppant contact-impact behavior in the fracture surface. In the numerical analysis, a material property of proppant and formation characteristics is introduced based on experimental investigation. The influences of formation load and resulted deformation of formation are calculated by total penetration of proppant. It has been found that the formation stresses on both sides of fractured result in high penetration of proppant in the fracture surfaces, although proppant remains un-deformed.
Author: Potcharaporn Pongthunya Publisher: ISBN: Category : Languages : en Pages :
Book Description
One of the most critical parameters in the success of a hydraulic fracturing treatment is to have sufficiently high fracture conductivity. Unbroken polymers can cause permeability impairment in the proppant pack and/or in the matrix along the fracture face. The objectives of this research project were to design and set up an experimental apparatus for dynamic fracture conductivity testing and to create a fracture conductivity test workflow standard. This entirely new dynamic fracture conductivity measurement will be used to perform extensive experiments to study fracturing fluid cleanup characteristics and investigate damage resulting from unbroken polymer gel in the proppant pack. The dynamic fracture conductivity experiment comprises two parts: pumping fracturing fluid into the cell and measuring proppant pack conductivity. I carefully designed the hydraulic fracturing laboratory to provide appropriate scaling of the field conditions experimentally. The specifications for each apparatus were carefully considered with flexibility for further studies and the capability of each apparatus was defined. I generated comprehensive experimental procedures for each experiment stage. By following the procedure, the experiment can run smoothly. Most of dry runs and experiments performed with sandstone were successful.
Author: Kan Wu Publisher: Elsevier ISBN: 0323953611 Category : Technology & Engineering Languages : en Pages : 296
Book Description
Fiber optic-based measurements are innovative tools for the oil and gas industry to utilize in monitoring wells in a variety of applications including geothermal activity. Monitoring unconventional reservoirs is still challenging due to complex subsurface conditions and current research focuses on qualitative interpretation of field data. Hydraulic Fracture Geometry Characterization from Fiber Optic-Based Strain Measurements delivers a critical reference for reservoir and completion engineers to better quantify the propagation process and evolution of fracture geometry with a forward model and novel inversion model. The reference reviews different fiber optic-based temperature, acoustic, and strain measurements for monitoring fracture behaviors and includes advantages and limitations of each measurement, giving engineers a better understanding of measurements applied in all types of subsurface formations. Stress/strain rate responses on rock deformation are given a holistic approach, including guidelines and an automatic algorithm for identification of fracture hits. Last, a novel inversion model is introduced to show how fracture geometry can be used for optimization on well placement decisions. Supported by case studies, Hydraulic Fracture Geometry Characterization from Fiber Optic-Based Strain Measurements gives today’s engineers better understanding of all complex subsurface measurements through fiber optic technology. Examine the basics of distributed fiber optic strain measurements Conduct a detailed analysis of strain responses observed in both horizontal and vertical monitoring wells Present a systematic approach for interpreting strain data measured in the field Highlight the significant insights and values that can be derived from the field measured strain dataset Support monitoring and modeling for subsurface energy extraction and safe storage
Author: Juan Correa Castro Publisher: ISBN: Category : Languages : en Pages :
Book Description
Unconventional gas has become an important resource to help meet our future energy demands. Although plentiful, it is difficult to produce this resource, when locked in a massive sedimentary formation. Among all unconventional gas resources, tight gas sands represent a big fraction and are often characterized by very low porosity and permeability associated with their producing formations, resulting in extremely low production rate. The low flow properties and the recovery factors of these sands make necessary continuous efforts to reduce costs and improve efficiency in all aspects of drilling, completion and production techniques. Many of the recent improvements have been in well completions and hydraulic fracturing. Thus, the main goal of a hydraulic fracture is to create a long, highly conductive fracture to facilitate the gas flow from the reservoir to the wellbore to obtain commercial production rates. Fracture conductivity depends on several factors, such as like the damage created by the gel during the treatment and the gel clean-up after the treatment. This research is focused on predicting more accurately the fracture conductivity, the gel damage created in fractures, and the fracture cleanup after a hydraulic fracture treatment under certain pressure and temperature conditions. Parameters that alter fracture conductivity, such as polymer concentration, breaker concentration and gas flow rate, are also examined in this study. A series of experiments, using a procedure of "dynamical fracture conductivity test," were carried out. This procedure simulates the proppant/frac fluid slurries flow into the fractures in a low-permeability rock, as it occurs in the field, using different combinations of polymer and breaker concentrations under reservoirs conditions. The result of this study provides the basis to optimize the fracturing fluids and the polymer loading at different reservoir conditions, which may result in a clean and conductive fracture. Success in improving this process will help to decrease capital expenditures and increase the production in unconventional tight gas reservoirs.
Author: Weiwei Wu (Ph. D.) Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
A large proportion of the hydraulic fractures created during a hydraulic fracturing treatment remain unpropped after hydraulic fracturing despite the significant quantities of proppant injected in the process. These fractures either have a fracture width smaller than the size of the proppants, or are too far away from the wellbore where proppant cannot reach. Their presence has been demonstrated and corroborated by multiple independent sources of evidence such as flowback, production and microseismic data. These unpropped fractures present a huge potential for production enhancement, since they possess a very large contact area with the reservoir. Unfortunately, this potential flow area is closed by the closure stress during production. Without the presence of proppants, unpropped fractures are expected to behave differently from propped fractures. In this study, fracture conductivities of unpropped fractures in shales are measured with preserved Eagle Ford and Utica shale cores to better understand their closure behavior, in particular those after exposure to fracturing fluids. The unpropped fractures exhibit fracture conductivities 2 to 4 orders of magnitude lower than those of propped fractures, and are more sensitive to closure stress. Plastic deformation is found to dominate the closure process, and strong hysteresis occurs in unpropped fracture conductivity with a 70-80% reduction after a loading-unloading cycle of closure stress. Exposure to water-based fracturing fluids reduces unpropped fracture conductivity by shale softening or fines production. Unpropped fracture conductivities also appear to be sensitive to shale mineralogy, which affects the shale mechanical properties and shale-fluid interaction. A numerical model is developed to simulate the closure of unpropped and natural fractures, and to compute their corresponding fracture conductivity. A conjugate gradient algorithm and fast Fourier transform technique are incorporated to dramatically enhance the computation efficiency. Plastic deformation and deformation interaction among asperities, ignored in some previous models, are considered and shown to play an important role in the closure process. The model is validated against analytical solutions and experiments, for both elastic-only and elastoplastic scenarios. The compliance of unpropped fractures is demonstrated to be sensitive to the roughness and hardness of fracture surfaces, while less affected by Young's modulus. The new model is also capable of simulating closure of heterogeneous fracture surfaces. More plastic deformation and lower fracture conductivity is measured when surfaces with high clay content are used. Given the same mineralogy, the mineral distribution pattern shows a smaller impact on the closure behavior. The possibility of employing acid fracturing to stimulate unpropped fractures is also explored. The acid-etched topography of shale fracture surfaces is found to be dependent on both the content and distribution of the carbonate minerals. Shales with a high carbonate content (over 60 wt%) generally tend to develop rougher acid-etched surfaces. However, more carbonate content does not always necessarily lead to increased etched roughness. High etched roughness is more likely developed from a blocky, rather than scattered, distribution of carbonate minerals. A new experimental method, the "half-core approach", is formulated to address the challenge caused by shale heterogeneity in experimentally evaluating and comparing fracture performance. The half-core approach splits one shale core into two half cores, which are then subjected to treatments of interest independently, followed by assemblage into individual full cores with a spacer for fracture conductivity measurement. The half-core approach is effective in creating a baseline with reduced sample variation among shales to improve evaluation of fracturing fluids. Similar mineralogy and mechanical properties are found between half-cores among preserved shale samples spanning a wide range of mineralogy from Barnett, Eagle Ford, Haynesville and Utica shales. By applying the half-core approach, acid fracturing is systematically benchmarked against brine with Eagle Ford shales categorized into low (below 40 wt%), medium (40-70 wt%) and high (over 70 wt%) carbonate content. Compared to brine exposure, non-uniform acid fracturing enhances unpropped fracture conductivities for shales for a wide range of carbonate contents, while uniform acid fracturing generally leads to lower fracture conductivities due to shale softening. The unetched zone in non-uniform etching reduces shale softening and creates a surface topography that enhances fracture flow. Channels are more likely to form in carbonate-rich shale (over 70 wt%). Development of channels substantially increases the unpropped fracture conductivity, and reduces the hysteresis of unpropped fracture conductivities to closure stress. The presence of carbonate veins is found to promote the development of non-uniform etching
Author: Mohammed Rashnur Rahman
Author: Mohammed Rashnur Rahman
Author: Kathryn Elizabeth Briggs
Author: Mark John McGinley
Author: Javed Akbar Khan
Author: Potcharaporn Pongthunya
Author: Jan-Erik Andersson
Author: Kan Wu
Author: Joseph F. Connell
Author: Juan Correa Castro
Author: Weiwei Wu (Ph. D.)