[PDF] Dna Based Tracers For Fractured Reservoir Characterization eBook

Author : Yuran Zhang
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Page : pages
File Size : 25,62 MB
Release : 2020
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A thorough understanding of the subsurface fracture network is crucial for the effective exploitation and management of geothermal energy, unconventional hydrocarbon resources, groundwater reservoirs, etc. While conventional tracer technology is a useful tool to characterize the complex network of flowpaths in geologic reservoirs, tracers are limited in unique variations and hence insufficient for characterizing reservoirs with a large number of wells. In addition, conventional tracer testing only provides a "snapshot" of the flowpath properties which may be inadequate for reservoirs that are subjected to changes. This research sought to resolve the limitations of conventional tracer testing by exploring novel, DNA-based tracer candidates. DNA's infinite number of unique sequences and hence great degree of specificity makes it a promising tracer candidate for improved subsurface characterization. We first investigated the use of uniquely designed, synthetic DNA fragments as injected tracers. The method to measure target-specific DNA tracer concentration is described. The effect of DNA sequence, fragment length and porous medium on DNA transport was studied to provide guidance to potential field applications and data interpretation. It was found that DNA transport was not affected by DNA sequence (i.e. the arrangement of nucleotides). The length of DNA fragments does not affect the shape of the tracer return curve, but does affect tracer mass recovery. Shorter DNA appeared to be more prone to adsorption, while longer DNA appeared to be more prone to size exclusion effect. We then extended the concept of DNA-based tracers towards the genomic DNA of fluid-associated microorganisms that naturally colonize a geologic reservoir. Instead of targeting just a few microbes, we proposed taking advantage of the entire microbial community population in a reservoir fluid sample as unique signatures pinpointing the origins of fluids. We tested this method at a mesoscale enhanced geothermal system (EGS) testbed at Sanford Underground Research Facility (SURF) by sampling indigenous fluids produced from separate fractures and analyzing their microbial community structure via high-throughput 16S rRNA gene amplicon sequencing. We found that hydraulically isolated fractures at our field site hosted distinct microbial community populations, demonstrating substantial microbial heterogeneity across fractures. However, locally within a fracture, the microbial community were relatively homogenized, serving as a unique natural tracer or "fingerprint" of the fracture. We demonstrated at our field site that sampling indigenous fluids from an undisturbed, newly developed reservoir could help us identify natural interwell connectivity when more than one well were drilled into the same natural fracture. Finally, building upon the idea of reservoir indigenous microbial populations as natural tracers, we investigated the potential of this novel data source in an actively circulating, dynamic reservoir. Again using the EGS testbed at SURF, we sampled the produced fluids from the reservoir that underwent long-term flow circulation. Sampling was conducted regularly in a 5-month time series and the microbial populations in the fluids were sequenced. We found that although the whole circulating reservoir were connected hydraulically, the difference in relative connectivity among fractures still allowed different flowing fractures to have different microbial community signatures. The long-term microbial monitoring at our site identified the switch of production zone of a borehole likely due to major changes in the fracture network. Changes in fracture network were also observed from microbial time-series data after a week-long injection halt, likely due to the reopened hydraulic fracture not restoring to its initial state. We thereby demonstrated that long-term microbial community monitoring in an active reservoir may effectively enable the direct observation of fracture network evolution. Such information is difficult to achieve via other reservoir diagnostic methods.

Author : Aymen Abduljalil Alramadhan
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Page : 311 pages
File Size : 14,55 MB
Release : 2013
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In order to understand the complex fracture network that controls water movement in Sherrod Area of Spraberry Field in West Texas and to better manage the on-going waterflood performance, a field scale inter-well tracer test was implemented. This test presents the largest inter-well tracer test in naturally fractured reservoirs reported in the industry and includes the injection of 13 different tracers and sampling of 110 producers in an area covering 6533 acres. Sherrod tracer test generated a total of 598 tracer responses from 51 out of the 110 sampled producers. Tracer responses showed a wide range of velocities from 14 ft/day to ultra-high velocities exceeding 10,000 ft/day with same-day tracer breakthrough. Re-injection of produced water has caused the tracers to be re-injected and added an additional challenge to diagnose and distinguish tracer responses affected by water recycling. Historical performance of the field showed simultaneous water breakthrough of a large number of wells covering entire Sherrod area. This research investigate analytical, numerical, and inversion modeling approaches in order to categorize, history match, and connect tracer responses with water-cut responses with the objective to construct multiple fracture realizations based entirely on water-cut and tracers' profiles. In addition, the research highlight best practices in the design of inter-well tracer tests in naturally fractured reservoirs through lessons learned from Sherrod Area. The large number of tracer responses from Sherrod case presents a case of naturally fractured reservoir characterization entirely based on dynamic data. Results indicates that tracer responses could be categorized based on statistical analysis of tracer recoveries of all pairs of injectors and producers with each category showing distinguishing behavior in tracers' movement and breakthrough time. In addition, it showed that tracer and water-cut responses in the field are dominantly controlled by the fracture system revealing minimum information about the matrix system. Numerical simulation studies showed limitation in dual porosity formulation/solvers to model tracer velocities exceeding 2200 ft/day. Inversion modeling using Gradzone Analysis showed that east and north-west of Sherrod have significantly lower pore volume compared to south-west. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151192

Author : Morgan F. Ames
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Page : pages
File Size : 49,16 MB
Release : 2016
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One of the most significant open problems in geothermal reservoir engineering is the development of a reliable and accurate method to predict thermal breakthrough. Such a method would enable more informed decisions to be made regarding reservoir management. Methods developed at present include analytical models and solute tracers, both of which have limitations. The use of particles as temperature-sensitive tracers is a promising approach due to the high degree of control of the physical and chemical properties of nanomaterials and micromaterials. Additionally, particles experience less matrix diffusion than solute tracers and tend to stay in high velocity fluid streamlines, which results in earlier particle breakthrough in the absence of significant particle deposition. These properties could potentially be exploited to infer temperature and measurement location, which could in turn provide useful information about thermal breakthrough. In order to assess whether particle tracers can provide more useful information about future thermal behavior of reservoirs than existing solute tracers, models were developed for both solute tracers and particle tracers. Three existing solute tracer types were modeled: conservative solute tracers (CSTs), reactive solute tracers with temperature-dependent reaction kinetics (RSTs), and sorbing solute tracers that sorb reversibly to fracture walls (SSTs). Additionally, three particle tracers which have not been developed in practice were modeled: dye-releasing tracers (DRTs) that release a solute dye at a specified temperature threshold, threshold nanoreactor tracers (TNRTs) with an encapsulated reaction that does not begin until a specified temperature threshold is reached, and temperature-time tracers (TTTs) capable of recording detailed temperature-time histories of each particle. In this study, TTTs represent the most informative tracer with respect to thermal breakthrough. These models were used in the context of an inverse problem in which synthetic tracer data were calculated for several "true" discrete fracture networks. Next, computational optimization was used to match these data by adjusting fracture location, length, and orientation for a variable number of fractures. Finally, the thermal behaviors of the fracture networks with the best fits to the data were compared to those of the true fracture networks, and the tracers were ranked according to their forecasting ability. Overall, thermal breakthrough forecast error was found to increase with fracture network complexity. However, in all cases, all tracers forecasted thermal breakthrough with unrealistic accuracy. This is partly due to neglecting thermal interference between closely spaced fractures in the thermal model. In all three cases, CSTs were found to be the least informative tracer type because they are insensitive to temperature. SSTs were also modeled as insensitive to temperature in this work, but they performed better than CSTs because sorption is sensitive to surface area, which is also closely related to a reservoir's thermal performance. In order to fully understand the relative informativity of these solute and particle tracers, a second study was performed using a uniform parallel fracture reservoir model that accounts for interference between fractures in both thermal and tracer transport. In this study, a seventh type of tracer test was also considered in which all three solute tracer types (CSTs, RSTs, and SSTs) were used simultaneously to gain the benefits of all three tracer types. This tracer type was designated ALLSOL, which is short for "all solutes." As with the discrete fracture network modeling study, synthetic data were generated and matched using optimization, after which thermal breakthrough forecasts were calculated. The decision variables used in optimization were the number of fractures and fracture length, width, aperture, and spacing. Two inverse problem scenarios with different fracture spacings were examined: 15 meter spacing and 5 meter spacing. In both scenarios, all individual solute tracers had significant error, particle tracers and ALLSOL forecasted thermal breakthrough more accurately than individual solute tracers, and ALLSOL had slightly more accurate forecasts than particle tracers. In the 15 meter spacing scenario, both RST and TNRT had very inaccurate forecasts because the temperature distribution is somewhat insensitive to fracture spacing at early time when fracture spacing is sufficiently large. This resulted in good matches and small objective function values for inaccurate estimates of fracture spacing. In order to determine if other tracers besides RST and TNRT are insensitive to spacing at early time when spacing is sufficiently large, the objective function values of all tracer types were evaluated using the optimal solution for TNRT in the 15 meter spacing scenario. Low objective function values and good fits to the data were observed for every tracer type except for TTT, indicating that TTT is the only tracer type considered that is capable of detecting differences in spacing at early time when the true fracture spacing is large. This is because the temperature is measured directly by the TTT rather than inferring the temperature from the return curve, as is the case for all other tracer types. In the 5 meter spacing case, the RST had a very inaccurate thermal breakthrough forecast because its return curve has a nonunique relationship with the temperature distribution (i.e. the RST return curve was matched by a reservoir with a significantly different temperature distribution from the true reservoir, which happened to result in the same amount of reaction). Forecast error was generally larger in the uniform parallel fracture modeling scenarios than in the discrete fracture network modeling scenarios. This demonstrates the importance of accounting for thermal interference in temperature-sensitive tracer modeling.

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File Size : 17,33 MB
Release : 1984
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Retention processes such as adsorption and diffusion into an immobile region can effect tracer movement through a fractured reservoir. This study has conducted experimental work and has developed a two-dimensional model to characterize retention processes. A method to directly determine some important flow parameters, such as the fracture aperture, from the analysis of tracer tests has been developed as a result of the new two-dimensional model. The experimental work consisted of batch experiments designed to both reproduce earlier work and to determine the magnitude of the retention effects. Negligible retention was observed from which it was concluded that the batch experiments were not sensitive enough and that more sensitive flowing tests were needed. A two-dimensional model that represents a fractured medium by a mobile region, in which convention, diffusion, and adsorption are allowed, and an immobile region in which only diffusion and adsorption are allowed has been developed. It was possible to demonstrate how each of the mass-transfer processes included in the model affect tracer return curves by producing return curves for any set of the defining variables. Field data from the New Zealand was numerically fit with the model. The optimum values of the parameters determined from curve fitting provided a direct estimate of the fracture width and could be used to estimate other important flow parameters if experimentally determinable values were known. 25 refs., 22 figs., 6 tabs.

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Page : pages
File Size : 24,22 MB
Release : 2005
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The transport of chemicals or heat in fractured reservoirs is strongly affected by the fracture-matrix interfacial area. In a vapor-dominated geothermal reservoir, this area can be estimated by inert gas tracer tests, where gas diffusion between the fracture and matrix causes the tracer breakthrough curve (BTC) to have a long tail determined by the interfacial area. For water-saturated conditions, recent studies suggest that sorbing solute tracers can also generate strong tails in BTCs that may allow a determination of the fracture-matrix interfacial area. To theoretically explore such a useful phenomenon, this paper develops an analytical solution for BTCs in slug-tracer tests in a water-saturated fractured reservoir. The solution shows that increased sorption should have the same effect on BTCs as an increase of the diffusion coefficient. The solution is useful for understanding transport mechanisms, verifying numerical codes, and for identifying appropriate chemicals as tracers for the characterization of fractured reservoirs.

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Page : pages
File Size : 21,81 MB
Release : 1987
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Tracer tests have been an important technique for determining the flow and reservoir characteristics in various rock matrix systems. While the interwell tracer tests are aimed at the characterization of the regions between the wells, single-well injection-backflow tracer tests may be useful tools of preliminary evaluation, before implementing long term interwell tracer tests. This work is concerned with the quantitative evaluation of the tracer return profiles obtained from single well injection-backflow tracer tests. First, two mathematical models of tracer transport through fractures, have been reviewed. These two models are based on two different principles: Taylor Dispersion along the fracture and simultaneous diffusion in and out of the adjacent matrix. Then the governing equations for the transport during the injection-backflow tests have been solved. Finally the results were applied to field data obtained from Raft River and East Mesa geothermal fields. In order to determine the values of the parameters of the models that define the transport mechanisms through fractures a non-linear optimization technique was employed. 26 refs., 10 figs.

Author : Akhil Datta-Gupta
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Page : pages
File Size : 32,49 MB
Release : 2005
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We explore the use of efficient streamline-based simulation approaches for modeling and analysis partitioning interwell tracer tests in heterogeneous and fractured hydrocarbon reservoirs. We compare the streamline-based history matching techniques developed during the first two years of the project with the industry standard assisted history matching. We enhance the widely used assisted history matching in two important aspects that can significantly improve its efficiency and effectiveness. First, we utilize streamline-derived analytic sensitivities to relate the changes in reservoir properties to the production response. These sensitivities can be computed analytically and contain much more information than that used in the assisted history matching. Second, we utilize the sensitivities in an optimization procedure to determine the spatial distribution and magnitude of the changes in reservoir parameters needed to improve the history-match. By intervening at each iteration during the optimization process, we can retain control over the history matching process as in assisted history matching. This allows us to accept, reject, or modify changes during the automatic history matching process. We demonstrate the power of our method using two field examples with model sizes ranging from 10{sup 5} to 10{sup 6} grid blocks and with over one hundred wells. We have also extended the streamline-based production data integration technique to naturally fractured reservoirs using the dual porosity approach. The principal features of our method are the extension of streamline-derived analytic sensitivities to account for matrix-fracture interactions and the use of our previously proposed generalized travel time inversion for history matching. Our proposed workflow has been demonstrated by using both a dual porosity streamline simulator and a commercial finite difference simulator. Our approach is computationally efficient and well suited for large scale field applications in naturally fractured reservoirs with changing field conditions. This considerably broadens the applicability of the streamline-based analysis of tracer data and field production history for characterization of heterogeneous and fractured reservoirs.

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Page : 8 pages
File Size : 48,3 MB
Release : 2004
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A key parameter governing the performance and life-time of a Hot Fractured Rock (HFR) reservoir is the effective heat transfer area between the fracture network and the matrix rock. We report on numerical modeling studies into the feasibility of using tracer tests for estimating heat transfer area. More specifically, we discuss simulation results of a new HFR characterization method which uses surface-sorbing tracers for which the adsorbed tracer mass is proportional to the fracture surface area per unit volume. Sorption in the rock matrix is treated with the conventional formulation in which tracer adsorption is volume-based. A slug of solute tracer migrating along a fracture is subject to diffusion across the fracture walls into the adjacent rock matrix. Such diffusion removes some of the tracer from the fluid in the fractures, reducing and retarding the peak in the breakthrough curve (BTC) of the tracer. After the slug has passed the concentration gradient reverses, causing back-diffusion from the rock matrix into the fracture, and giving rise to a long tail in the BTC of the solute. These effects become stronger for larger fracture-matrix interface area, potentially providing a means for estimating this area. Previous field tests and modeling studies have demonstrated characteristic tailing in BTCs for volatile tracers in vapor-dominated reservoirs. Simulated BTCs for solute tracers in single-phase liquid systems show much weaker tails, as would be expected because diffusivities are much smaller in the aqueous than in the gas phase, by a factor of order 1000. A much stronger signal of fracture-matrix interaction can be obtained when sorbing tracers are used. We have performed simulation studies of surface-sorbing tracers by implementing a model in which the adsorbed tracer mass is assumed proportional to the fracture-matrix surface area per unit volume. The results show that sorbing tracers generate stronger tails in BTCs, corresponding to an effective enhancement of diffusion. Tailing in BTCs for sorbing tracers may provide adequate sensitivity for quantifying the fracture-matrix interface area. We discuss requirements for tracer sorption and present considerations for designing a tracer test that would determine fracture-matrix interface area.