Browsing by Subject "Unconventional"
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Item Analysis of Water Based Fracture Fluid Flowback to Determine Fluid/Shale Chemical Interaction(2014-12-18) Agim, Kelechi NConcerns about the substantial amounts of water and chemicals pumped into the subsurface during hydraulic fracturing are valid because long term effects of these stimulation actions are unknown at the present time. Although less than 1% of the hydraulic fracturing fluid composition is made up of the various chemicals, reactions are likely to occur when said chemicals are in contact with other elements from the rock. To reduce the amount of water being used in these fracture treatments, flowback from stimulated reservoirs are considered as base fluid to prepare additional fracture fluid. However, in order re-use the fluid, it must be treated appropriately since the produced waters are chemically altered. Hence, the changes that ensue in both the rock and fluid have to be studied and quantified where possible. Shale samples from the Barnett, Eagle Ford and Marcellus were exposed to a cross-linked gel composition for 1, 5, 10 and 30 days at simulated reservoir conditions (elevated temperature and pressure). Collected samples were sent to a commercial laboratory for analysis. Concentration of the cations, anions and dissolved metals in the fluid were measured before and after contact with the rock to establish any reactions that might have taken place. To uncover the effects of hydraulic fracturing treatment on the different rock types, the mineralogy was determined using X-Ray fluorescence (XRF). Also, tests of total organic content (TOC) were performed to ascertain what kinds of changes may have affected the elements within the rock. Differences in measured quantities of cations, anions etc. confirm that chemical reactions occur. Furthermore, the variations observed between the base fluid and those exposed to the different shale types corroborate that the different composition of elements in the rocks can be correlated to the different concentrations of measured properties of the simulated flowback.Item Evaluation of Membrane Treatment Technology to Optimize and Reduce Hypersalinity Content of Produced Brine for Reuse in Unconventional Gas Wells(2012-10-19) Eboagwu, UcheOver 18 billion barrels of waste fluids are generated annually from oil and gas production in the United States. As a large amount of water is used for oilfield operations, treating and reusing produced water can cut the consumption of fresh water in well sites. This research has helped to develop a membrane process train for a mobile produced water treatment unit for treating oilfield produced brine for reuse. To design the process train, over 30 sets of combination tests at pilot laboratory scale were performed using pretreatment, microfiltration and nanofiltration processes. Membrane performance was selected based on high flux separation efficiency, high tolerance for solids and fluid treatments. Over 95 % solids rejection and greater than 80 % oil removal efficiency were obtained in all these tests. Process train (pre-treatment and membrane) performance was monitored by chemical analysis of permeate and models fitting experimental data for the process. From the results, hydrocarbon rejection was analyzed; total organic carbon rejection was 47.9 %, total carbon content averaged 37.3 % rejection and total inorganic carbon rejection was at 3.66 %. BTEX removal efficiency ranged from 0.98 % to 52.7 % with the progressive pretreatment methods of using cartridge filters. The nanofiltration membrane showed significant reduction in total dissolved solids and in both anionic and cationic species. The process train is seen to follow a sequence of treatment from cartridge and oil removal filter treatment to microfiltration treatment to ultrafiltration, followed by nanofiltration for the purpose of this research. Further research still needs to be done on to determine the kind of analytical test which will give real time feedback on effectiveness of filters. In summary, the process train developed by TAMU-GPRI possesses distinct advantages in treating oilfield produced brine using membrane technology. These advantages include high quality of permeate, reduced sludge and the possibility of total recycle water systems. The small space requirement, moderate capital costs and ease of operation associated with the use of the mobile unit membrane technology also makes it a very competitive alternative to conventional technologies.Item A general poro-elastic model for pad-scale fracturing of horizontal wells(2015-12) Manchanda, Ripudaman; Sharma, Mukul M.; Espinoza, David N; McClure, Mark W; Olson, Jon E; Roussel, Nicolas PEconomic production of oil and gas from tight rocks requires horizontal well drilling with multiple hydraulic fractures along the length of the horizontal wells. Multiple horizontal wells are drilled and fractured close to each other to increase the recovery of oil and gas from a single location or pad. Interference between fractures in a horizontal well pad is commonly observed in the field. There is no clear understanding of the impact of various operational and reservoir parameters on the observed interference. This inter-well interference can occur through the creation of complex fracture networks and/or poro-elastic stress changes. In this research, the development of a poro-elastic numerical simulator was undertaken to evaluate hydraulic fracturing practices in pad-scale scenarios. The primary motivation was to assess the impact of various operational parameters such as fracture spacing, well spacing and fracture sequencing on the geometry of the created fractures. Two approaches were used to understand the problem at hand. In the first approach, static fractures were simulated in 3-D and the impact of their stress shadow on subsequent fractures was studied. It was observed that fracture spacing, injection volume, and time between successive fractures were the most important parameters that could be used to optimize the creation of fractures in a well. Formation properties such as Young’s modulus and horizontal stress contrast modified the magnitude and spatial extent of the stress shadow and the extent of stress reorientation. It was shown that stage spacing, well spacing and fracture sequencing together with fracture designs (volume of sand pumped and fluids used) can be adjusted to obtain non-intersecting, transverse fractures that efficiently drain the reservoir. A hypothesis, time dependent closure of induced unpropped fractures, was presented to explain why zipper fracturing often outperforms conventional sequential fracturing. The hypothesis was tested and confirmed with a field data set made available to us by Shell from the Eagle Ford shale. In the second approach, a novel finite volume based 3-D, geomechanical, field-scale numerical simulator was developed to simulate propagation of multiple fractures simultaneously in a poro-elastic reservoir. This provided a more realistic model of the pad-scale fracturing process. The ability of the model to perform realistic pad-scale simulations was demonstrated for a variety of field situations such as multi-cluster multi-stage fracturing, infill-well fracturing, re-fracturing, mini-frac analysis and fracture network simulations. The inclusion of poro-elastic effects and reservoir heterogeneity in the model allowed us to examine the effects of reservoir depletion on fracture geometry in refraced and infill wells.Item Investigation of analytical models incorporating geomechanical effects on production performance of hydraulically and naturally fractured unconventional reservoirs(2014-08) Aybar, Umut; Sepehrnoori, Kamy, 1951-; Patzek, Tadeusz W.Petroleum and Geosystems EngineeringItem Minimizing Water Production from Unconventional Gas Wells Using a Novel Environmentally Benign Polymer Gel System(2012-02-14) Gakhar, KushExcess water production is a major economic and environmental problem for the oil and gas industry. The cost of processing excess water runs into billions of dollars. Polymer gel technology has been successfully used in controlling water influx without damaging hydrocarbon production in conventional naturally fractured or hydraulically fractured reservoirs. However, there has been no systematic investigation on effectiveness and placement conditions of polymer gels for shutting off water flow from fractures with narrow apertures in shale and tight gas reservoirs. The existing polymer gels, like those based on Chromium(III) Acetate, as a crosslinker will exert very high extrusion pressure to effectively penetrate the narrow aperture fractures present in shale and tight gas reservoirs. This gives rise to a need for a new polymer gel system that can be used for selectively shutting off water flow from narrow aperture fractures in shale and tight gas reservoirs. The new gel system will have a longer gelation time than the existing polymer gels; this ensures minimum crosslinking of the gel by the time it reaches bottom hole. The gelant solution will be pumped at low pressure so that, it penetrates only pre-existing fractures in the formation with ease. This study for the first time focuses on developing an environmentally benign polymer gel system based on high molecular weight HPAM, as a base polymer and a commercial grade PEI as an organic crosslinker. Gel samples of different concentration ratios of the polymer and crosslinker were prepared and classified under Sydansk code of gel strength to find optimum concentration ratios that gave good gels. The gel system was characterized using Brookfield DV-III Ultra Rheometer and Fann-35 Viscometer.Item Probabilistic Performance Forecasting for Unconventional Reservoirs With Stretched-Exponential Model(2011-08-08) Can, BunyaminReserves estimation in an unconventional-reservoir setting is a daunting task because of geologic uncertainty and complex flow patterns evolving in a long-stimulated horizontal well, among other variables. To tackle this complex problem, we present a reserves-evaluation workflow that couples the traditional decline-curve analysis with a probabilistic forecasting frame. The stretched-exponential production decline model (SEPD) underpins the production behavior. Our recovery appraisal workflow has two different applications: forecasting probabilistic future performance of wells that have production history; and forecasting production from new wells without production data. For the new field case, numerical model runs are made in accord with the statistical design of experiments for a range of design variables pertinent to the field of interest. In contrast, for the producing wells the early-time data often need adjustments owing to restimulation, installation of artificial-lift, etc. to focus on the decline trend. Thereafter, production data of either new or existing wells are grouped in accord with initial rates to obtain common SEPD parameters for similar wells. After determining the distribution of model parameters using well grouping, the methodology establishes a probabilistic forecast for individual wells. We present a probabilistic performance forecasting methodology in unconventional reservoirs for wells with and without production history. Unlike other probabilistic forecasting tools, grouping wells with similar production character allows estimation of self-consistent SEPD parameters and alleviates the burden of having to define uncertainties associated with reservoir and well-completion parameters.Item Revised productivity index equation to improve transient history match for the Capacitance Resistance Model(2016-12) Pan, Zhong; Lake, Larry W.The Capacitance Resistance Model (CRM) is a data-driven reservoir model developed for well surveillance and management. The model is gaining popularity in reservoir engineering community because of its simplicity and ability to provide insights on well-to-well connectivity during water/gas flooding project. Furthermore, the model can be used to optimize injection scheme or even plan for infill drilling. The model was built on the assumptions that during waterflooding the dominant flow regime is semi-steady state. However, to extend the functionality of this model to unconventional reservoirs, a productivity index model that works well in transient flow regime should be investigated. In this thesis, two different productivity models are proposed. The first is the combined productivity index model. This model originates from the analytical solution of single compartment model and the constant behavior of the productivity index in fracture-dominated flow. These two components are then linearly combined to form a new productivity index model. The second is the logistic productivity index model, which uses a well-studied logistic growth model to capture the S-shaped production profile starting from a transient linear flow regime to a late-time fracture-dominated regime. These two proposed productivity index models are incorporated into the fundamental CRM equation, respectively, to derive the logistic CRM and combined CRM. To validate the models, multiple reservoir simulations were conducted to generate synthetic cases capturing both transient linear flow and fracture-dominated regime, and then the proposed models were fitted to the simulation data using Microsoft Excel Solver. Case validation is also accomplished with field data. Very good history matches were obtained from these two models, and they demonstrate that with proper revision to semi-steady state model CRM is able to match production history sufficiently and quickly. In addition, the combined CRM is physics-based so it is shown that the model is able to provide insights on some important reservoir properties.Item Zonal isolation improvement through enhanced cement-shale bonding(2014-12) Liu, Xiangyu, active 21st century; Oort, Eric vanThe incompatibility of cement and shale and the subsequent failure of primary cementing jobs is a very significant concern in the oil & gas industry. On wells ranging from hydraulically fractured shale land wells to deepwater wells, this incompatibility leads to an increased risk in failing to isolate zones, which could possibly present a well control hazard and can lead to sustained casing pressure. The cement-shale interface presents a weak link that often becomes compromised by the loads incurred either during drilling, completion/stimulation or production phases. To formulate cements for effective zonal isolation, it is crucial to evaluate the bond strength of the cement-shale interface. Although several studies have focused on the interactions between cement and sandstone, very few studies have addressed the bonding behavior of cement with shale. The conventional push-out test protocol used to measure cement-to-sandstone shear bond strength has proven to be difficult to apply on shale due to its laminated or brittle nature that complicates sample preparation and can lead to shale or cement matrix failure instead of failure at the interface. In this paper, we present a novel, simple and versatile laboratory test procedure to measure the shear bond strength between cement and shale. The new procedure was used to develop cement formulations to improve the cement-to-shale bond. Two different design approaches were investigated. One involves introducing Gilsonite into cement to maintain shale integrity. The second design involves using surfactant to improve cement interfacial sealing property. Our results indicate that bond strength of cement with shale can be enhanced significantly incorporating surfactant in cement slurries.