Every gas well ceases producing as reservoir pressure depletes. The usual liquid presence in the reservoir can cause further problems by accumulating in the wellbore and reducing production even more. There are a number of options in well completion to prevent liquid loading even before it becomes a problem. Tubing size and perforation interval optimization are the two most common methods. Although completion optimization will prevent liquid accumulation in the wellbore for a certain time, eventually as the reservoir pressure decreases more, the well will start loading. As liquid loading occurs it is crucial to recognize the problem at early stages and select a suitable prevention method. There are various methods to prevent liquid loading such as / gas lift, plunger lift, pumping and velocity string installation. This study set out to construct a decision tree for a possible expert system used to determine the best result for a particular gas well. The findings are tested to confirm by field applications as attempts of the expert system.

Gas hydrates are crystalline compounds made of gas and water molecules. Methane hydrates are found in marine sediments and permafrost regions; extensive amounts of methane are trapped in the form of hydrates. The unique behavior of hydrate-bearing sediments requires the development of special research tools, including new numerical algorithms (tube- and pore-network models) and experimental devices (high pressure chambers and micromodels). Hydraulic conductivity decreases with increasing variance in pore size distribution; while spatial correlation in pore size reduces this trend, both variability and spatial correlation promote flow focusing. Invading gas forms a percolating path while nucleating gas forms isolated gas bubbles; as a result, relative gas conductivity is lower for gas nucleation than for gas invasion processes, and constitutive models must be properly adapted for reservoir simulations. Physical properties such as gas solubility, salinity, pore size, and mixed gas conditions affect hydrate formation and dissociation; implications include oscillatory transient hydrate formation, dissolution within the hydrate stability field, initial hydrate lens formation, and phase boundary changes in real field situations. High initial hydrate saturation and high depressurization favor gas recovery efficiency during gas production from hydrate-bearing sediments. Even a small fraction of fines in otherwise clean sand sediments can cause fines migration and concentration, vuggy structure formation, and gas-driven fracture formation during gas production by depressurization.

Gas wells suffer a decrease in productivity because of the formation of a liquid hydrocarbon “condensate” in the near wellbore area. This "condensate" forms near producing wells when the flowing pressure is below the reservoir fluid's dew point. Several methods have been shown to temporarily alleviate this problem, but eventually the condensate bank reforms and the productivity again decreases. The use of surfactants to alter the near wellbore wettability to neutral wetting is a potential longer term solution to liquid blocking in these reservoirs. This alteration increases the gas and liquid relative permeabilities and thereby the productivity by reducing the residual liquid saturation. This enhancement allows the accumulated liquid to flow and is durable as long as the wettability alteration is persistent. This solution has been shown to be successful through core flood experiments and field trials in high permeability sandstones, but no improvements had been observed in low permeability cores. As the global demand for energy increases, the petroleum industry has begun to develop unconventional (low permeability) assets, new techniques are needed to maintain and improve their productivity. Liquid blocking in these wells can have a much larger impact on both the gas and condensate production in such low permeability formations. Applying this technique increases both gas and condensate mobility and should increase the economic producing life of these wells. Core flood experiments were conducted to investigate the ability of a chemical treatment to alter the wettability of low permeability sandstones. Previous experimentation did not find any improvement because the increased capillary forces prevented the treatment solution from being easily displaced. This concealed the benefit achieved when the wettability was altered. These experiments recorded smaller relative permeability increases compared to higher permeability core floods, so super critical carbon dioxide was tested as an alternative solvent. While the new treatment was more injectable, it was not as successful at altering wettability. Progress has been made on a solution to liquid blocking in low permeability sandstones, but additional research needs to be completed to further optimize this method. / text

Depressurization is thought to be a promising method for gas recovery from methane hydrate reservoirs, but considerable water production is expected when this method is applied to the hydrate reservoir of high initial water saturation. In this case, the prediction of water production is a critical problem. This study examined relative permeability curves during hydrate dissociation by comparing numerical simulations with laboratory experiments. Data of gas and water volumes produced during depressurization were taken from gas recovery experiments using sand-packed cores containing methane hydrates. In each experiment, hydrates were dissociated by depressurization at a constant pressure. The surrounding temperature was held constant during dissociation. The volumes of gas and water produced, the temperatures inside of the core, and the pressures at the both ends of the core were measured continuously. The experimental results were compared with numerical simulations by using the simulator MH21-HYDRES (MH21 Hydrate Reservoir Simulator). The experimental results showed that considerable volume of water was produced during hydrate dissociation, and the simulator could not reproduce the large water production when we used typical relative permeability curves such as the Corey model. To obtain good matching for the volumes of gas and water produced during hydrate dissociation, the shape of relative permeability curves was modified to express the rapid decrease in gas permeability with increasing water saturation. This result suggests that the connate water can be easily displaced by hydrate-dissociated gas and move forward in the hydrate reservoir of high initial water saturation.

In this study / gas production by depressurization method from a hydrate reservoir containing free gas zone below the hydrate zone is numerically modeled through 3 dimensional, 3 phase, non-isothermal reservoir simulation. The endothermic nature of hydrate decomposition requires modeling to be non-isothermal / hence energy balance equations must be employed in the simulation process. TOUGH-Fx, the successor of the well known multipurpose reservoir simulator TOUGH2 (Pruess [24]) and its very first module TOUGH-Fx/Hydrate, both developed by Moridis et.al [23] at LBNL, are utilized to model production from a theoretical hydrate reservoir, which is first studied by Holder [11] and then by Moridis [22], for comparison purposes. The study involves 2 different reservoir models, one with 30% gas in the hydrate zone (case 1) and other one with 30% water in the hydrate zone (case 2). These models are further investigated for the effect of well-bore heating. The prominent results of the modeling study are: &amp / #8226 / In case 1, second dissociation front develops at the top of hydrate zone and most substantial methane release from the hydrate occurs there. &amp / #8226 / In case 2 (hydrate-water in the hydrate zone), because a second dissociation front at the top of hydrate zone could not fully develop due to high capillary pressure acting on liquid phase, a structure similar to ice lens formation is observed. &amp / #8226 / Initial cumulative replenishment (first 5 years) and the replenishment rate (first 3.5 years) are higher for case 2 because, production pressure drop is felt all over the reservoir due to low compressibility of water and more hydrate is decomposed. Compared to previous works of Holder [11] and Moridis [22], amount of released gas contribution within the first 3 years of production is significantly low which is primarily attributed to the specified high capillary pressure function.

Na alimentação animal, o sorgo pode ser explorado de diversas formas. Além dos grãos, a planta pode ser oferecida na forma de silagem, rolão, verde ou ainda pastejada; embora o valor nutritivo pode sofrer algumas variações pela presença ou ausência de compostos fenólicos como os taninos condensados. O objetivo deste trabalho foi avaliar a composição química-bromatológica, qualidade fermentativa e produção de gases in vitro nas silagens de sorgo granífero adicionados com diferentes níveis de guandu. O estudo foi dividido em dois experimentos. O primeiro estudo (Capítulo 3) avaliou os efeitos da adição de forragem de guandu sobre a composição química-bromatológica e fermentativas da silagem de sorgo granífero. Os tratamentos foram compostos por: T1 - Silagem com 100% de sorgo, T2 - Silagem com 25% de guandu e 75% de sorgo, T3 - Silagem com 50% de guandu e 50% de sorgo, T4 - Silagem com 75% de guandu e 25% de sorgo e T5 Silagem com 100% de guandu. As variáveis estudadas para a composição química e fermentativas das silagens foram: matéria seca (MS), proteína bruta (PB), fibra em detergente neutro (FDN), fibra em detergente neutro (FDA), carboidratos totais (CHOT), matéria mineral (MM), fenóis totais (FT), taninos totais (TT), taninos condensados (TC), pH, capacidade tampão (CT), perdas fermentativas e ácido lático. A adição de guandu promoveu efeito linear (P<0,01) nas silagens para os teores de MS, PB, FDN, FDA, FT, assim como para as perdas fermentativas de MS da silagem. Enquanto para os teores de CHOT, MM e TC verificaram-se respostas quadráticas (p<0,01) entre as silagens. Inclusões de 25, 50 e 75% de guandu, com base na matéria fresca, seriam suficientes para melhorar o valor nutricional assim como para se obter melhor padrão fermentativo da silagem de sorgo. O segundo estudo (Capítulo 4) avaliou a produção total de gases, metano, degradabilidade da MS (DMS) e degradabilidade da MO (DMO) em silagens de sorgo granífero com níveis crescentes de guandu através da técnica in vitro de produção de gases. Foram avaliadas as cinco silagens de sorgo granífero com níveis crescentes (0, 25, 50, 75 e 100%) de guandu utilizados como substratos. Para avaliar o efeito do tanino nas silagens sobre a produção de gases, procedeu-se um bioensaio, no qual os substratos foram incubados na presença de polietileno glicol (PEG), macro molécula capaz de ligar-se aos taninos presente no substrato, liberando os nutrientes para a fermentação; sendo o efeito do tanino medido pelo incremento na produção de gases. Não houve diferença estatística para a produção total de gases e metano para os níveis de inclusão do guandu, entretanto houve diferença significativa para o contraste nível zero e a inclusão do guandu. Para os incrementos também não houve diferença significativa para as variáveis (PG, CH4, DMS e DMO). Por outro lado, houve maior PG e maior incremento para o nível de 25% de guandu com a presença do PEG. Foi encontrado maior emissão de metano e incremento de metano para o nível 50% de guandu, quando comparado com os demais níveis. Houve maior DMS e DMO no substrato com 100% de guandu com a presença do PEG. Concluiu-se que a adição de forragem de guandu na silagem de sorgo aumentou o conteúdo de PB e reduziu os teores de FDN, implicando um melhor valor nutritivo das silagens, contudo os taninos condensados precisariam ser monitorados para futuros experimentos in vivo / In animal nutrition, sorghum can be used in various ways. Besides grain, the plant can be offered as silage, pollard, green or even grazed. Although the nutritional value may undergo some changes by the presence or absence of phenolic compounds such as condensed tannins. The objective of this study was to evaluate the chemical composition, fermentation quality and gas production in vitro in sorghum silage added with different levels of pigeon pea. The study was divided into two experiments. The first study (Chapter 3) evaluated the effects of the addition of pigeon pea grass on the chemical composition and fermentation of sorghum silage. The treatments were: T1 - silage with 100% sorghum, T2 - silage with 25% of pigeon pea and sorghum 75%, T3 - silage with 50% of pigeon pea and sorghum 50%, T4 - silage with 75% pigeon pea and 25% of sorghum and T5 - silage with 100% pigeon pea. The parameters of chemical composition and fermentation of the silage were: dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), total carbohydrates (TCHO), ash, total phenolics (TP), total tannins (TT), condensed tannins (CT), pH, buffer capacity (BC), losses of fermentation and lactic acid. The addition of pigeon pea showed linear effect (P <0.01) in silage for DM, CP, NDF, ADF, TP, as well as the levels of CT and fermentation losses in DM of silage. As for the contents of TCHO, CT and MM there were quadratic responses (p <0.01) among silages. The results observed that, inclusion of 25, 50 and 75% pigeon pea, based on fresh weight, are sufficient to improve the nutritional value and to achieve better fermentation pattern of sorghum silage. The second study (Chapter 4) evaluated the production of gases, methane, DM degradability and degradability of OM in silage sorghum with increasing levels of pigeon pea using the technique of bioassay gas production. Five types of grain sorghum silage with increasing levels (0, 25, 50, 75 and 100%) of pigeon pea were used as substrates and evaluated by gás production technique. There were no significant differences with and without the presence of PEG within each level using regression, for (GP, CH4 and DMD), but there were significant effect for using of contrast for the variables (GP, CH4 and OMD). No significant difference was observed for the increments for the variables (GP and CH4,). On the other hand GP was more increase in the level of 25% of pigeon pea in the presence of PEG. Compared with the other levels of pigeon pea the level 50% showed higher emissions of methane. In the presence of PEG,DMD and OMD Showed higher percentage on the substrate with 100% of pigeon pea . it can be concluded that ,the addition of pigeon pea in sorghum silage increased the PC content and decreased the NDF, implying a higher nutritive value of silages, but the tannins need to be monitored for future experiments in vivo

Com o objetivo de estudar o uso de inóculo de fezes em substituição do conteúdo ruminal de bubalinos na técnica in vitro de produção de gases, este presente trabalho comparou as avaliações realizadas em três ensaios. Foram utilizados três bubalinos da raça Mediterrâneo, machos, adultos, castrados, fistulados no rúmen com média de peso vivo de 450 (± 18,7) kg. Estes animais receberam uma dieta basal, composta de silagem de milho (70%) e concentrado (30%). Estes animais foram os doadores dos 2 tipos de inóculos, que foram conteúdo ruminal (CR) e fezes. O primeiro ensaio realizado foi com alimentos concentrados: grão de milho, farelo de soja, farelo de trigo e farelo de algodão; o segundo ensaio foi com leguminosas forrageiras: alfafa (Medicago sativa L. ), estilosantes pioneiro (Stylosanthes macrocephala cv. Pioneiro), soja perene (Neonotonia wightii) e leucena (Leucaena leucocephala); e o terceiro e último ensaio foi realizado com gramíneas forrageiras: capim braquiarão (Brachiaria brizantha cv. Marandu), capim buffel (Cenchrus ciliaris L. cv. Biloela), estrela africana (Cynodon plectostachyus) e capim mombaça (Panicum maximum Jacq. cv. Mombaça). Os valores médios obtidos de produção potencial de gases em cada ensaio foram menores (P&lt;0,05) para as amostras fermentadas com inóculos de fezes que com conteúdo ruminal, sendo respectivamente, para concentrados (140,23 e 194,08 mL.g-1MS), gramíneas (161,99 e 230,25 mL.g-1MS) e leguminosas (141,78 e 170,70 mL.gm-1MS). Conclui-se que inóculos de fezes não apresentam condições satisfatórias para substituição do inóculum com conteúdo ruminal para uso na técnica de produção in vitro de gases. / In order to study the use of faeces as inoculum as alternative for buffalo rumen contents in the in vitro gas production technique, the present work evaluations of three tests. We used three Mediterranean buffalos, male, adult, neutered, fistulated in the rumen, with an average live weight of 450 (± 18.7) kg. These animals received a basal diet composed of corn silage (70%) and concentrated (30%). These buffalo were the donors of the two types of inocula, rumen content (CR) and faeces. The first test was carried out with concentrate foods: corn grain, soybean meal, wheat bran and cottonseed meal, the second test was with legumes: alfalfa (Medicago sativa L. ), Pioneiro estilo (Stylosanthes macrocephala cv. Pioneiro) , perennial soybean (Neonotonia wightii) and leucaena (Leucaena leucocephala) and the third and last test was carried out with grasses: Marandu grass (Brachiaria brizantha cv. Marandu), buffel grass (Cenchrus ciliaris L. cv. Biloela), African Star grass (Cynodon plectostachyus) and Mombasa grass (Panicum maximum Jacq. cv. Mombasa). The average values of potential production of gas in each test were lower (P&lt;0.05) for samples fermented with an inoculum of faeces with rumen contents, being respectively, for concentrates (140.23 and 194.08 mL.g-1MS), grasses (161.99 and 230.25 mL.g-1MS) and legumes (141.78 and 170.70 mL.g-1MS). It follows that fecal inoculum unsatisfactory condition for replacing the inoculum with rumen technique for use in the in vitro production of gases technique.

O uso da suplementação com levedura viva em equinos tem sido estudado, pelo potencial de redução da produção de lactato no intestino grosso sendo relatado por alguns autores, melhora da digestibilidade aparente da proteína bruta. Porém, o uso de levedura viva protegida ainda não foi relatado para a espécie. O objetivo do trabalho foi avaliar a digestibilidade aparente dos nutrientes e parâmetros de fermentação intestinal e gástrica com a suplementação de levedura viva e levedura viva protegida em equinos em manutenção. O delineamento experimental foi o quadrado latino duplo balanceado com oito animais, quatro dietas avaliados por quatro períodos de 22 dias cada, sendo 15 dias de adaptação à dieta, 5 dias de coleta de fezes (CTF), 1 dia para coleta de conteúdo gástrico e 2 semanas de intervalo entre os períodos. As médias dos tratamentos foram comparadas através de contrastes ortogonais (C1: controle [CTR] versus levedura [LEV], levedura protegida [PROT] e levedura viva + levedura protegida [L + P]; C2: L + P versus LEV e PROT; C3: LEV versus PROT). O nível de significância do teste utilizado foi a 10%. Não foram observados efeitos para pH nas fezes, concentração sérica de fator tumoral alfa, concentrações de ácido lático e ácidos de cadeia curta nas diferentes dietas. Não foi observado significância para a digestibilidade aparente dos nutrientes da dieta quando se usou levedura viva ou protegida (P=0,0683). Houve aumento das concentrações de ácido acético com o uso de levedura no conteúdo gástrico (P=0,0082). Avaliando a técnica de coleta sugerida, a adaptação realizada para este procedimento de coleta de digesta gástrica apresentou fácil aplicabilidade, com alta tolerância pelos equinos, além de proporcionar perfeita precisão do local de coleta a ser avaliado. A levedura viva e levedura protegida não apresentam efeito quanto a degradabilidade in vitro da matéria seca e da fibra em detergente neutro (P &gt; 0,05). A fermentação com inóculo de fezes possui maiores taxas de produção de gás quando se utiliza feno como substrato e suplementação com levedura viva (P=0,0190). Quando se utiliza de conteúdo gástrico como inóculo, a levedura protegida apresenta menor produção de gases (P=0,0484). / The use of live yeast supplementation in equines has been studied for the potential reduction of lactate production in the large intestine and is reported by some authors to improve the apparent digestibility of crude protein. However, the use of protected live yeast has not yet been reported for the species. The aim of this study was to evaluate the apparent digestibility of nutrients and parameters of intestinal and gastric fermentation with the supplementation of live yeast and protected live yeast in horses. The experimental design was the double balanced latin square with eight animals, four diets evaluated for four periods of 22 days each, being 15 days of adaptation to the diet, 5 days of collection of feces (CTF), 1 day for collection of gastric content and 2 weeks interval between periods. The treatments were compared by means of orthogonal contrasts (C1: control [CTR] versus yeast [LEV], protected yeast [PROT] and live yeast + protected yeast [L + P]; C3: LEV versus PROT). The level of significance of the test used was 10%. No effects were observed for faecal pH, serum concentration of alpha tumor factor, lactic acid concentrations and short chain acids in the different diets. It was no possible to observe a difference significance on apparent digestibility in nutrients of diets when living or protected yeast (P = 0.0683). There was an increase in acetic acid concentrations with the use of yeast in gastric contents (P = 0.0082). Evaluating the suggested collection technique, the adaptation performed for this procedure of gastric digestion was easy to apply, with high tolerance by the horses, besides providing perfect accuracy of the collection site to be evaluated. Live yeast and protected yeast have no effect on the in vitro degradability of dry matter and neutral detergent fiber (P&gt; 0.05). Fermentation with fecal inoculum has higher rates of gas production when hay is used as a substrate and supplementation with live yeast (P = 0.0190). When gastric contents are used as the inoculum, the protected yeast presents lower gas production (P = 0.0484).

Air pollutants and greenhouse gases are two groups of important trace components in the earth’s atmosphere that can affect local air quality, be detrimental to the human health and ecosystem, and cause climate change. Human activities, especially the energy use and energy production processes, are responsible for a significant share of air pollutants and greenhouse gases in the atmosphere. In this work, I specifically focused on characterizing air pollutants and greenhouse gas emissions from the on-road gasoline and diesel vehicles, which is an important energy use process that largely contributes to the urban air pollutions, and from the natural gas production systems, which is a major energy production process that has increased dramatically in recent years and is expected to have a long-lasting impact in the future. We conducted multi-seasonal measurements in the Fort Pitt Tunnel in Pittsburgh, PA to update the on-road vehicle emission factors, to measure the size distribution of vehicle emitted particulate matter (PM), and to quantify the volatility distributions of the vehicle emitter primary organic aerosol (POA). We also conducted mobile measurements in the Denver-Julesburg Basin, the Uintah Basin, and the Marcellus Shale to quantify facility-level VOC emission from natural gas production facilities, and I constructed a gridded (0.1° × 0.1°) methane emission inventory of natural gas production and distribution over the contiguous US. I found that the stricter emission standards were effective on regulating NOx and PM emissions of diesel vehicles and the NOx, CO and organic carbon (OC) emissions of gasoline vehicles, while the elemental carbon (EC) emissions of gasoline vehicles did not change too much over the past three decades. Vehicle-emitted particles may be largely externally mixed, and a large fraction of vehicle-emitted particles may be purely composed of volatile component. Vehicle-emitted smaller particles (10– 60 nm) are dominantly (over 75%) composed of volatile component. The size-resolved particles and particles emission factors for both gasoline and diesel vehicles are also reported in this work. I also found that the POA volatility distribution measured in the dynamometer studies can be applied to describe gas-particle partitioning of ambient POA emissions. The POA volatility distribution measured in the tunnel does not have significant diurnal or seasonal variations, which indicate that a single volatility distribution is adequate to describe the gas-particle partitioning of vehicle emitted POA in the urban environment. The facility-level VOC emission rates measured at gas production facilities in all three gas production fields are highly variable and cross a range of ~2-3 order of magnitudes. It suggests that a single VOC emission profile may not be able to characterize VOC emissions from all natural gas production facilities. My gridded methane emission inventory over the contiguous US show higher methane emissions over major natural gas production fields compared with the Environmental Protection Agency Inventory of US Greenhouse Gas Emission and Sinks (EPA GHGI) and the Emission Database for Global Atmospheric Research, version 4.2 (Edgar v4.2). The total methane emissions of the natural gas production and distribution sector estimated by my inventory are 74% and 20% higher than the Edgar v4.2 and EPA GHGI, respectively. I also run the GEOS-Chem methane simulation with my inventory and EPA GHGI and compare with the GOSAT satellite data, and results show that my inventory can improve the model and satellite comparison, but the improvement is very limited. The size-resolved emission factors of vehicle emitted particles and POA volatility distribution reported in this work can be applied by the chemical transport models to better quantify the contribution of vehicle emissions to the PM in the atmosphere. Since our measurement of VOC emissions of natural gas production facilities were conducted before EPA started to regulate VOC emissions from the O&NG production facilities in 2016, the facility-level VOC emission rates reported in this work can serve as the basis for future studies to test the effectiveness of the regulatory policies. The spatially resolved methane emission inventory of natural gas production and distribution constructed in this work can be applied to update the current default methane emission inventory of GEOS-Chem, and the updated methane emission inventory can be used as a better a priori emission field for top-down studies that inversely estimate methane emissions from atmospheric methane observation.

Tidal freshwater wetland soils contain large amounts of organic carbon, some of which is mineralized to carbon dioxide (CO2) and methane (CH4) by a diverse consortium of anaerobic microorganisms that includes fermenters, syntrophs, and methanogens (MG). These microbial groups are tightly linked and often rely on cooperative interspecies metabolisms (i.e., syntrophy) to survive. Environmental perturbations can disrupt these interactions and thus alter the rates and pathways of carbon cycling. One environmental change of particular concern in coastal wetlands is sea level rise, which can result in increased episodic saltwater intrusion events into these ecosystems. These events cause an influx of sulfate (SO4-2) to the soils and may stimulate sulfate-reducing bacteria (SRB), which can directly compete with syntrophs for energy sources (e.g., fermentation products such as butyrate). Since syntroph metabolism generates byproducts that serve as the energy source for many MG, this competition can have indirect negative effects on methanogenesis. In addition, SRB can directly compete with MG for these byproducts, particularly formate, H2, and/or acetate. The goal of this study was to understand how both MG and syntroph-MG consortia respond to and recover from SRB competition during an episodic saltwater intrusion event. To achieve this, microcosms containing soil slurry from a freshwater wetland were subjected to simulated saltwater intrusion, and metabolic inhibitors were used to isolate the activity of the various functional groups. This study focused on the breakdown of butyrate, which is a key energy source in syntroph‑MG consortia metabolisms. The observed changes in butyrate breakdown rates and byproduct accumulation during butyrate degradation assays confirmed that butyrate breakdown was mediated through syntroph-MG consortia, and that formate, rather than H2, was likely used as an electron carrier during syntrophic activity. Additions of SO4‑2 (as Na2SO4) to the freshwater microcosms stimulated SRB activity and shifted the MG community to favor acetoclastic members. These changes were accompanied by a 24% increase in CO2 production and an 80% decrease in CH4 production. Interestingly, when NaCl was added to achieve similar ionic strength, CH4 production decreased by ~32%, suggesting SRB competition is not the only factor affecting methanogenesis. Butyrate degradation rates demonstrated that while SRB were strong competitors for butyrate, concurrent syntrophic metabolism was possible. Further, data show that SRB were poor competitors for acetate, which could explain the increase in acetoclastic MG. Following removal of SRB competition, CH4 production recovered but only by ~50% after 28 days, which suggests that some MG communities in tidal freshwater wetlands may not be resilient to saltwater intrusion events. Over this same time, rates of syntrophic butyrate breakdown largely recovered, but butyrate breakdown resulted in the production of less CH4 and acetate and more CO2 and formate, indicating saltwater intrusion events may lead to persistent changes in the byproducts and pathways of carbon breakdown in tidal freshwater wetlands.