Browsing by Subject "Fracture conductivity"
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Item Creation and Impairment of Hydraulic Fracture Conductivity in Shale Formations(2014-07-10) Zhang, JunjingMulti-stage hydraulic fracturing is the key to the success of many shale gas and shale oil reservoirs. The main objectives of hydraulic fracturing in shale are to create artificial fracture networks that are conductive for oil and gas flow and extensive into the reservoir for high and long-lasting production, while economical to keep the well commercial. Due to the variation in shale mineralogical and mechanical properties, mechanisms of fracture conductivity creation in shale formations are complicated. Standard fracture conductivity measurement procedures were developed for high concentration propped fractures and need to be modified to measure the conductivity of unpropped fractures and the low concentration proppant packs. Water-based fracturing fluids can interact with the clay minerals in shale and eventually impact shale fracture conductivity. All these challenges require more studies to elevate the understanding of shale fracture conductivity creation and impairment. The aims of this work are to design an experimental framework to measure fracture conductivity created by different mechanisms, to develop a correlation calibrated by the experimental data to predict shale fracture conductivity, and to investigate the mechanisms of conductivity damage by water. We first present the laboratory procedures and experimental design that can accurately measure fracture conductivity of shale fractures. Then, a program is developed to calculate conductivity considering the physical processes that dictate propped fracture conductivity as observed in the experiments. After the undamaged shale fracture conductivity is measured by dry nitrogen, water with similar flowback water compositions is flowed to simulate the damage process followed by the second gas flow to measure the recovered fracture conductivity after the water damage. From this study, we find that the unpropped shale fractures are conductive up to certain closure stress by a variety of mechanisms. The correlation we develop can capture the physical processes in the shale fracture and can reasonably predict propped fracture conductivity. Shale fracture surface softening is identified as the dominant cause for the significant conductivity reduction after water flow. The systematic study on realistic shale fracture conductivity is the foundation of well performance analysis and production history matching. The investigation on water damage can better guide the fracturing design in shale reservoirs.Item Experimental study of the effect of stress and fluid sensitivity on propped and un-propped fracture conductivity in preserved reservoir shale(2016-05) Kakkar, Pratik; Sharma, Mukul M.; Daigle, Hugh CA good amount of work has been done on analyzing the effect of stress and fluid sensitivity on fracture conductivity in sandstones. This thesis tries to answer similar questions with regard to shale formations. Shales are very sensitive to aqueous fluids and their mechanical properties change when exposed to it. This mechanical property change in shale is mainly caused due to clay swelling. Some of the previous researchers working on shale fluid sensitivity failed to use preserved reservoir cores for their experiments and allowed them to dry out. This study has been conducted on preserved Utica and Eagle Ford core samples. Experiments were conducted to study the effect of effective stress on propped and un-propped fracture conductivity. These experiments were conducted at reservoir temperature and pressure conditions to mimic field conditions. Different fluids were flowed through the fracture to compare the effect of different fluids on fracture conductivity. To prevent clay swelling various clay stabilizers are used in the field during drilling and fracturing operations. Experiments were conducted to test the effectiveness of different clay stabilizers in preventing fracture conductivity reduction. Some of the clay stabilizers were more effective than others but all of them were unable to prevent fracture conductivity reduction when fracture was flowed with a high pH fluid.Item Impact of salt-tolerant friction reducers on shale stability and fracture conductivity(2014-08) Mimouni, Arielle Simone; Katz, Lynn Ellen; Oort, Eric van; Sharma, Mukul M.One of the main challenges of hydraulic fracturing is the reuse of flowback waters. While it alleviates the disposal and treatment costs of these concentrated brines, it also limits the environmental impacts of the fracking industry by reducing the amounts of fresh water necessary to produce gas. This research aims at optimizing this process by assessing the impacts of salt-tolerant friction reducers on shale stability and fracture conductivity. Polyacrylamide and polyethylene oxide based friction reducers were assessed over a wide range of NaCl and CaCl₂ concentrations, using a hot rolling oven and fracture conductivity experiments. The commonly used polyacrylamide based DR3046 was found to be a good shale stabilizer but did not efficiently reduce friction in the presence of divalent salts. While high molecular weight polyethylene oxides showed a high friction reduction in all brines, and reduced shale cuttings dispersion in the presence of salts, they did not maintain fracture conductivity. The newly developed Dispersion Polymer Friction Reducer (DPFR) showed the best and most consistent results for all salt concentrations, in terms of friction reduction, shale stabilization efficiency, and ability to maintain the highest fracture conductivity.Item A study of the effect of stress and fluid sensitivity on propped fracture conductivity in preserved reservoir shales(2013-05) Pedlow, John Wesley; Sharma, Mukul M.A sizable amount of literature exists analyzing the effect of confining stress on fracture conductivity in sandstones. This thesis attempts to answer similar questions with regard to shale formations. The low Young’s Moduli and Brinell hardness values characteristic of many prospective shale formations may lead to a great deal of embedment and fines production which can drastically reduce fracture conductivity. Furthermore, shales exhibit sensitivity to aqueous fluids which may cause them to be weakened in the presence of certain fracturing fluids. Previous work analyzing shale fluid sensitivity has failed to preserve the shales’ formation properties by allowing the shale to dry out. This paper presents a study of propped fracture conductivity experiments at reservoir temperature and pressure using various North American shale reservoir cores. Exposure to the atmosphere can alter the mechanical properties of the shale by either drying or hydrating the samples, so care was taken to preserve these shales in their native state by maintaining constant water activity (relative humidity). Variations in applied closure stress and aqueous fluid exposure were analyzed and in certain cases altered the propped fracture conductivity by crushing proppant, embedding the proppant into the fracture face, and producing fines. The damage to fracture conductivity is correlated to mineralogy for the various shale samples. These findings show that a one-size-fits-all frac design will not work in every shale formation, rather a tailored approach to each shale is necessary. In the future, the results of this work will be analyzed alongside easier to perform Brinell hardness tests, swelling tests, and other characterization techniques incorporated into the UT Shale Characterization Protocol. Correlations were developed to relate the simpler tests to the fracture conductivity experiments which yield a straight forward method to determine the role embedment and fluid sensitivity have on post treatment fracture conductivity in shales. The UT Shale characterization Protocol can then be used to optimize the design and execution of fracing treatments.