Natural Gas Wells Research Articles

Unified Decline Type-Curve Analysis for Natural Gas Wells in Boundary-Dominated Flow

SummaryRate-time decline-curve analysis is the technique most extensively used by engineers in the evaluation of well performance, production forecasting, and prediction of original fluids in place. Results from this analysis have key implications for economic decisions surrounding asset acquisition and investment planning in hydrocarbon production. State-of-the-art natural gas decline-curve analysis heavily relies on the use of liquid (oil) type curves combined with the concepts of pseudopressure and pseudotime and/or empirical curve fitting of rate-time production data using the Arps hyperbolic decline model. In this study, we present the analytical decline equation that models production from gas wells producing at constant pressure under boundary-dominated flow (BDF) which neither employs empirical concepts from Arps decline models nor necessitates explicit calculations of pseudofunctions. New-generation analytical decline equations for BDF are presented for gas wells producing at (1) full production potential under true wide-open decline and (2) partial production potential under less than wide-open decline. The proposed analytical model enables the generation of type-curves for the analysis of natural gas reservoirs producing at constant pressure and under BDF for both full and partial production potential. A universal, single-line gas type curve is shown to be straightforwardly derived for any gas well producing at its full potential under radial BDF. The resulting type curves can be used to forecast boundary-dominated performance and predict original gas in place without (1) iterative procedures, (2) prior knowledge of reservoir storage properties or geological data, and (3) pseudopressure or pseudotime transformations of production data obtained in the field.

Studies investigate effects of hydraulic fracturing

The use of hydraulic fracturing, also known as fracking, to enhance the retrieval of natural gas from shale has been increasing dramatically—the number of natural gas wells rose about 50% since 2000. Shale gas has been hailed as a relatively low‐cost, abundant energy source that is cleaner than coal. However, fracking involves injecting large volumes of water, sand, and chemicals into deep shale gas reservoirs under high pressure to open fractures through which the gas can travel, and the process has generated much controversy. The popular press, advocacy organizations, and the documentary film Gasland by Josh Fox have helped bring this issue to a broad audience. Many have suggested that fracking has resulted in contaminated drinking water supplies, enhanced seismic activity, demands for large quantities of water that compete with other uses, and challenges in managing large volumes of resulting wastewater. As demand for expanded domestic energy production intensifies, there is potential for substantially increased use of fracking together with other recovery techniques for “unconventional gas resources,” like extended horizontal drilling.

Response of mule deer to habitat modification near natural gas development

Mule deer ( Odocoileus hemionus ) are known to shift habitat use in response to environmental modifications, including those associated with energy development. Their specific behavioral responses, however, and capacities to habituate to particular aspects of energy development have not been effectively studied. We examined mule deer response to habitat alteration near natural gas wells in Las Animas County, Colorado, USA in 2008—2010, an area experiencing development for extraction of natural gas. We created 10-1 ha openings in forests adjacent to 10 wells by removing standing trees in 2008, with concomitant establishment of 10 1-ha control sites adjacent to the same wells. On each site, we estimated deer use, indexed by pellet density, before and after tree removal. Concurrently, we measured plant production, cover, nutritional quality, species composition and biomass removed by deer and other large herbivores. Species richness and diversity and graminoid and forb cover and biomass increased on cut sites following tree removal. Use increased following tree removal on cut and control sites, but was greater on cut sites in 2010. Herbivores removed negligible quantities of vegetation on control sites in both years, suggesting that control sites may have been used primarily for concealment. Mule deer demonstrated the behavioral capacity to habituate to habitat modifications and other environmental changes associated with development for the extraction of energy. Managing forage and habitat availability appears to have the potential to affect the type of response and degree of habituation by mule deer to such development.

Unknown Quantity: Regulating Radionuclides in Tap Water

Radioactivity surrounds us; each day we are exposed to a certain amount by virtue of being alive on planet Earth. Some of this exposure comes from radioactive substances (radionuclides) that occur naturally in a wide variety of geologic and soil formations. Occasionally these naturally occurring substances become more concentrated or accessible through human activities such as mining and nuclear energy production, resulting in greater potential for exposure than their original natural occurrence would suggest. Other radionuclides are artificially created. Residents in almost all parts of the United States live on lands that contain minor to substantial concentrations of radionuclides of one type or another.1 These substances often make their way into tap water, leading to exposures by ingestion, inhalation, or dermal pathways during showering or other contact with the water. Although radionuclides are widespread, there are large gaps in our knowledge about sources of these materials, their distribution, associated health risks, and mitigation measures. However, the information we do have suggests that current drinking water standards for radionuclides established by the U.S. Environmental Protection Agency (EPA) may not adequately protect health. The EPA is set to review these standards relatively soon, and the next two years are prime time for filling in numerous information gaps and doing other legwork to make sure the review is as well informed as possible.

Response of Elk to Habitat Modification Near Natural Gas Development

Elk (Cervus elaphus) are known to shift habitat use in response to environmental modifications, including those associated with various forms of energy development. The specific behavioral responses underlying these trends, however, have not been effectively studied. To investigate such effects, we examined elk response to habitat alteration near natural gas wells in Las Animas County, Colorado, USA in 2008-2010. We created 10 1-ha openings in forests adjacent to 10 operating natural gas wells by removing standing timber in 2008, with concomitant establishment of 10 1-ha control sites adjacent to the same wells. On each site, we estimated elk use, indexed by pellet density, before and after timber removal. Concurrently, we measured plant production and cover, nutritional quality, species composition and biomass removed by elk and other large herbivores. Species richness and diversity, graminoid and forb cover, and graminoid and forb biomass increased on cut sites following tree removal. Differences were greater in 2010 than in 2009, and elk and deer removed more plant biomass in 2010 than 2009. Elk use of cut sites was 37% lower than control sites in 2009, but 46% higher in 2010. The initially lower use of cut sites may be attributable to lack of winter forage on these sites caused by timber removal and associated surface modification. The increased use of cut sites in 2010 suggested that elk possessed the behavioral capacity, over time, to exploit enhanced forage resources in the proximity of habitat modifications and human activity associated with maintenance of operating natural gas wells.

The Future of Fracking: New Rules Target Air Emissions for Cleaner Natural Gas Production

Natural gas is lauded as a cleaner-burning fuel than either coal or oil, but getting the fuel out of the ground can be a dirty process, especially given the widespread adoption of the technology known as hydraulic fracturing (“fracking”). Concerns about toxic air emissions from previously unregulated fracking sites led to the U.S. Environmental Protection Agency (EPA) announcement on 18 April 2012 of new and updated air pollution regulations for these facilities and certain other elements of oil and natural gas production and transmission.1 Compliance with the new regulations is expected to result in major reductions in emissions of methane and volatile organic compounds (VOCs), particularly from new fracked natural gas wells. The rules were a hot topic nationally, drawing more than 156,000 comments after the proposed version was released in mid-2011. Under the final rules, companies have until January 2015 to fully phase in the control measures needed; by comparison, the initial proposal called for a 60-day phase-in for many major requirements. The EPA says about half of all new wells already use the equipment needed to capture the targeted emissions.2 A hydraulic fracturing natural gas drilling rig on the eastern Colorado plains. In 2009 there were more than 38,000 natural gas wells in the state. Many environmental groups consider the new regulations an improvement over the existing situation, but they tend to be disappointed much more wasn’t done. “This is quite a milestone,” says Jeremy Nichols, Climate and Energy Program director for the advocacy group WildEarth Guardians, one of two groups that filed suit against the EPA in 2009 to force action on the issue. “But is the work done? No, of course not. It’s a floor to build on, providing a minimal level of protection.” The oil and natural gas industry has its own concerns about the new rules but has indicated it can work with them. In a press release issued the day the rules were announced, Howard Feldman, director of regulatory and scientific affairs for the American Petroleum Institute, said, “EPA has made some improvements in the rules that allow our companies to continue reducing emissions while producing the oil and natural gas our country needs.”3

Bacterial Communities Associated with Production Facilities of Two Newly Drilled Thermogenic Natural Gas Wells in the Barnett Shale (Texas, USA)

We monitored the bacterial communities in the gas-water separator and water storage tank of two newly drilled natural gas wells in the Barnett Shale in north central Texas, using a 16S rRNA gene pyrosequencing approach over a period of 6 months. Overall, the communities were composed mainly of moderately halophilic and halotolerant members of the phyla Firmicutes and Proteobacteria (classes Βeta-, Gamma-, and Epsilonproteobacteria) in both wells at all sampling times and locations. Many of the observed lineages were encountered in prior investigations of microbial communities from various fossil fluid formations and production facilities. In all of the samples, multiple H(2)S-producing lineages were encountered; belonging to the sulfate- and sulfur-reducing class Deltaproteobacteria, order Clostridiales, and phylum Synergistetes, as well as the thiosulfate-reducing order Halanaerobiales. The bacterial communities from the separator and tank samples bore little resemblance to the bacterial communities in the drilling mud and hydraulic-fracture waters that were used to drill these wells, suggesting the in situ development of the unique bacterial communities in such well components was in response to the prevalent geochemical conditions present. Conversely, comparison of the bacterial communities on temporal and spatial scales suggested the establishment of a core microbial community in each sampled location. The results provide the first overview of bacterial dynamics and colonization patterns in newly drilled, thermogenic natural gas wells and highlights patterns of spatial and temporal variability observed in bacterial communities in natural gas production facilities.

Electric regulation: The fracking buzz

AbstractA news media buzz has solidified around the economic and environmental impacts resulting from hydraulic fracturing in natural gas wells. The strictest opponents of hydraulic fracturing assert environmental degradation threatens ecological and human health to a degree that is high enough to require the government to prohibit use of the technique. Proponents assert the need to develop this newly accessed source of safe domestic energy as a key component to the “nation's clean energy future.”

Four-compartment partition model of hazardous components in hydraulic fracturing fluid additives

Mass balance principles were applied to a four-compartment partition model for 12 different hazardous components of hydraulic fracturing fluid additives used in 47 completed natural gas wells in the Marcellus Shale. Spill scenarios were modeled as if 1000 gallons of diluted additive were discharged into a surface water body or onto soil. Resulting concentrations were ranked according to magnitude, providing a relative comparison of quantities to be expected in each compartment. Highest mass concentrations in the water, soil and biota compartments were due to sodium hydroxide, 4,4-dimethyl oxazolidine, and hydrochloric acid. 4,4-dimethyl oxazolidine ranked highest in the air compartment.

A critical assessment of the efficacy of biocides used during the hydraulic fracturing process in shale natural gas wells

We examined the efficacy of multiple biocides that are commonly used to control sulfate-reducing bacteria in fracturing fluids in shale natural gas formations. Seven biocides (tetrakis [hydroxymethyl] phosphonium sulfate, sodium hypochlorite, didecyldimethylammonium chloride, tri-n-butyl tetradecyl phosphonium chloride, glutaraldehyde, a glutaraldehyde and alkyldimethylbenzylammonium chloride blend, and a glutaraldehyde alkyldimethylethylbenzylammonium chloride blend) were examined. Minimum inhibitory concentrations (MIC) were determined using planktonic cells and biofilms of Desulfovibrio desulfuricans strain G20 and a sulfate-reducing enrichment culture that was obtained from a Barnett Shale frac pond. All biocides had higher MIC values for biofilms compared to planktonic cells from these two cultures. Higher concentrations of all biocides, except didecyldimethylammonium chloride, were required to kill planktonic cells of G20 that were exposed to humic acid. These results clearly indicate that biofilm formation by sulfate-reducing bacteria, as well as organic loading rates, negatively impact the efficacy of biocides. This work provides valuable information concerning the effects of biofilm formation and organic loading on biocide MIC values. These MIC data can be used as a guide for the control of microbial growth in future frac jobs, which should result in fewer incidences of sulfide production and corrosion in shale natural gas wells.

Temporal and hierarchical spatial components of animal occurrence: conserving seasonal habitat for greater sage‐grouse

Developing strategies for sustainable management of landscapes requires research that bridges regionally important ecological and socioeconomic issues, and that aims to provide solutions to sustainability problems. We integrated Global Positioning Systems (GPS) telemetry and statistical modeling to quantify hierarchical spatial and temporal components of occurrence among greater sage‐grouse (Centrocercus urophasianus;n= 87), a species of conservation concern, with the larger goal of developing spatially‐explicit guidance for conservation of important winter habitat in a Wyoming, USA landscape undergoing development for energy resources. The pattern of occurrence at the landscape level (second‐order) and within seasonal use areas (third‐order) included selection for shrub vegetation with a prominent sagebrush (Artemisiaspp.) component, and avoidance of rough terrain, mesic areas, and human activity. A change in resource selection behavior across the diel cycle was not an apparent component of the higher‐order selection process; however, at the finer scale of investigation sage‐grouse shifted behavior across the diel cycle in ways likely related to risk aversion or maintaining a favorable thermal environment (i.e., day‐time‐only avoidance of natural gas wells and night‐time‐only selection for taller shrubs). At both spatial scales there was considerably more variation among individuals in the sign of their association with anthropogenic features than with vegetation and terrain. The final spatially‐explicit model, which depicted lower‐order selection (local, patch‐level, and seasonal use area) across the diel cycle constrained by selection processes at a higher order (second‐order), validated well, offering specific guidance for managing human activity and sage‐grouse conservation in the study area, and general guidance in developing sustainable landscape management strategies when animal occurrence reflects multiple spatial and temporal processes.

Optimized foamers for natural gas well deliquification: A statistical design approach

Liquid foamers have gained their popularity in deliquifying aged natural gas wells and coal bed methane wells due to their cost effectiveness and ease of application. Foamers are usually combinational products with Corrosion Inhibitors (CIs) and Scale Inhibitors (SIs) included to provide additional benefits such as corrosion protection and addressing the scaling issues in these applications. Organic solvents are often used to improve secondary properties such as pour point, viscosity and/or pumpablity of the foamer formulations. Designing an effective multi-functional foamer is more an art than science in production chemicals for the oil and gas industry. In this paper, Design of Experiments (DOE) methods were utilized to investigate synergism and antagonism in foamer formulations containing different surfactants, CI and Ethylene Glycol Monobutyl Ether (EGMBE) as the winterization solvent. Correlations between formulation compositions and performances such as liquid unloading efficiency, corrosion protection, pour point and cost effectiveness were studied. Models were developed based on these correlations and validated for performance prediction. In addition, the synergism observed in liquid unloading performance of formulations containing binary surfactants mixture was probed by studying the Critical Micelle Concentration (CMC) and molecular interaction in aqueous solutions. The composition of mixed micelles and the interaction parameter β obtained using Rubingh’s theory, were also discussed.

Landscape features and weather influence nest survival of a ground-nesting bird of conservation concern, the greater sage-grouse, in human-altered environments

Ground-nesting birds experience high levels of nest predation. However, birds can make selection decisions related to nest site location and characteristics that may result in physical, visual, and olfactory impediments to predators. We studied daily survival rate [DSR] of greater sage-grouse (Centrocercus urophasianus) from 2008 to 2010 in an area in Wyoming experiencing large-scale alterations to the landscape. We used generalized linear mixed models to model fixed and random effects, and a correlation within nesting attempts, individual birds, and years. Predation of the nest was the most common source of nest failure (84.7%) followed by direct predation of the female (13.6%). Generally, landscape variables at the nest site (≤ 30 m) were more influential on DSR of nests than features at larger spatial scales. Percentage of shrub canopy cover at the nest site (15-m scale) and distances to natural gas wells and mesic areas had a positive relationship with DSR of nests, whereas distance to roads had a negative relationship with DSR of nests. When added to the vegetation model, maximum wind speed on the day of nest failure and a 1-day lag in precipitation (i.e., precipitation the day before failure) improved model fit whereby both variables negatively influenced DSR of nests. Nest site characteristics that reduce visibility (i.e., shrub canopy cover) have the potential to reduce depredation, whereas anthropogenic (i.e., distance to wells) and mesic landscape features appear to facilitate depredation. Last, predators may be more efficient at locating nests under certain weather conditions (i.e., high winds and moisture).

Evaluating the Effect of Natural Gas Developments on Highways

The natural gas reserve in the Barnett Shale geological formation is one of the largest onshore natural gas reserves in the United States. The development of a natural gas well is a traffic-intensive operation that involves high volumes of truck traffic; saltwater traffic generated during the production phase is a major contributor to truck volume. The effect of traffic related to the natural gas industry on Texas highways is quantified. The oversized and overweight database maintained by the Texas Department of Transportation (DOT) was used to quantify several key characteristics of the rig traffic. In addition, personnel from the Texas DOT's Fort Worth District provided critical information about construction and saltwater traffic, including truck types used, gross vehicular weights, number of trips, and haul distances. Pavement sections were located along the busiest trucking corridors to evaluate damage caused by the truck traffic associated with natural gas development. Results indicated the approximate damage due to rig traffic was 1.6%, to construction traffic was 13%, and to saltwater traffic was 6%, relative to the damage caused by design traffic in terms of rutting. Additional damage caused by the natural gas truck traffic translated into reduced service life for pavements in the region. Results indicated a reduced service life of approximately 5.6%, 29%, and 16% associated with rig, construction, and saltwater traffic, respectively, in terms of rutting.

Well Completion for Effective Deliquification of Natural Gas Wells

Liquid loading has been a problem in natural gas wells for several decades. With gas fields becoming mature and gas production rates dropping below the critical rate, deliquification becomes more and more critical for continuous productivity and profitability of gas wells. Current methods for solving liquid loading in the wellbore include plunger lift, velocity string, surfactant, foam, well cycling, pumps, compression, swabbing, and gas lift. All these methods are to optimize the lifting of liquid up to surface, which increases the operating cost, onshore, and offshore. However, the near-wellbore liquid loading is critical but not well understood. Through numerical reservoir simulation studies, effect of liquid loading on gas productivity and recovery has been quantified in two aspects: backup pressure and near-wellbore liquid blocking by considering variable reservoir permeability, reservoir pressure, formation thickness, liquid production rate, and geology. Based on the new knowledge, we have developed well completion methods for effective deliquifications. These lead to better field operations and increased ultimate gas recovery.

Recovery optimization of membrane processes for treatment of produced water with high silica content

Disc tube (DT) and spiral wound (SW) configurations of nanofiltration (NF) and reverse osmosis (RO) processes were tested at pilot-scale using a two-pass configuration to treat produced water obtained from natural gas wells. First pass NF membranes were used to remove divalent cations from produced water. Permeate from the first pass NF membranes were used as feed to second pass RO membranes after increasing the pH to 10.0 to enhance silica solubility. To reduce the fouling potential on NF and RO membranes dissolved air floatation (DAF), ceramic ultrafiltration (UF), MYCELX cartridges, and organoclay filters were tested as pretreatment alternatives. Pretreatment processes were effective for turbidity and oil and grease removal but were not efficient in retaining organic matter, primarily protein-like and polysaccharide-like material, which eventually fouled the first pass NF membranes. The second pass RO membranes were scaled predominantly by silica. The overall feed water recovery of the two-pass NF-RO s...

Bacterial communities associated with hydraulic fracturing fluids in thermogenic natural gas wells in North Central Texas, USA

Hydraulic fracturing is used to increase the permeability of shale gas formations and involves pumping large volumes of fluids into these formations. A portion of the frac fluid remains in the formation after the fracturing process is complete, which could potentially contribute to deleterious microbially induced processes in natural gas wells. Here, we report on the geochemical and microbiological properties of frac and flowback waters from two newly drilled natural gas wells in the Barnett Shale in North Central Texas. Most probable number studies showed that biocide treatments did not kill all the bacteria in the fracturing fluids. Pyrosequencing-based 16S rRNA diversity analyses indicated that the microbial communities in the flowback waters were less diverse and completely distinct from the communities in frac waters. These differences in frac and flowback water communities appeared to reflect changes in the geochemistry of fracturing fluids that occurred during the frac process. The flowback communities also appeared well adapted to survive biocide treatments and the anoxic conditions and high temperatures encountered in the Barnett Shale.

Energy Return on Energy Invested for Tight Gas Wells in the Appalachian Basin, United States of America

The energy cost of drilling a natural gas well has never been publicly addressed in terms of the actual fuels and energy required to generate the physical materials consumed in construction. Part of the reason for this is that drilling practices are typically regarded as proprietary; hence the required information is difficult to obtain. We propose that conventional tight gas wells that have marginal production characteristics provide a baseline for energy return on energy invested (EROI) analyses. To develop an understanding of baseline energy requirements for natural gas extraction, we examined production from a mature shallow gas field composed of vertical wells in Pennsylvania and materials used in the drilling and completion of individual wells. The data were derived from state maintained databases and reports, personal experience as a production geologist, personal interviews with industry representatives, and literature sources. We examined only the “upstream” energy cost of providing gas and provide a minimal estimate of energy cost because of uncertainty about some inputs. Of the materials examined, steel and diesel fuel accounted for more than two-thirds of the energy cost for well construction. Average energy cost per foot for a tight gas well in Indiana County is 0.59 GJ per foot. Available production data for this natural gas play was used to calculate energy return on energy invested ratios (EROI) between 67:1 and 120:1, which depends mostly on the amount of materials consumed, drilling time, and highly variable production. Accounting for such inputs as chemicals used in well treatment, materials used to construct drill bits and drill pipe, post-gathering pipeline construction, and well completion maintenance would decrease EROI by an unknown amount. This study provides energy constraints at the single-well scale for the energy requirements for drilling in geologically simple systems. The energy and monetary costs of wells from Indiana County, Pennsylvania are useful for constructing an EROI model of United States natural gas production, which suggests a peak in the EROI of gas production, has already occurred twice in the past century.

Identifying and Prioritizing Greater Sage-Grouse Nesting and Brood-Rearing Habitat for Conservation in Human-Modified Landscapes

BackgroundBalancing animal conservation and human use of the landscape is an ongoing scientific and practical challenge throughout the world. We investigated reproductive success in female greater sage-grouse (Centrocercus urophasianus) relative to seasonal patterns of resource selection, with the larger goal of developing a spatially-explicit framework for managing human activity and sage-grouse conservation at the landscape level.Methodology/Principal FindingsWe integrated field-observation, Global Positioning Systems telemetry, and statistical modeling to quantify the spatial pattern of occurrence and risk during nesting and brood-rearing. We linked occurrence and risk models to provide spatially-explicit indices of habitat-performance relationships. As part of the analysis, we offer novel biological information on resource selection during egg-laying, incubation, and night. The spatial pattern of occurrence during all reproductive phases was driven largely by selection or avoidance of terrain features and vegetation, with little variation explained by anthropogenic features. Specifically, sage-grouse consistently avoided rough terrain, selected for moderate shrub cover at the patch level (within 90 m2), and selected for mesic habitat in mid and late brood-rearing phases. In contrast, risk of nest and brood failure was structured by proximity to anthropogenic features including natural gas wells and human-created mesic areas, as well as vegetation features such as shrub cover.Conclusions/SignificanceRisk in this and perhaps other human-modified landscapes is a top-down (i.e., human-mediated) process that would most effectively be minimized by developing a better understanding of specific mechanisms (e.g., predator subsidization) driving observed patterns, and using habitat-performance indices such as those developed herein for spatially-explicit guidance of conservation intervention. Working under the hypothesis that industrial activity structures risk by enhancing predator abundance or effectiveness, we offer specific recommendations for maintaining high-performance habitat and reducing low-performance habitat, particularly relative to the nesting phase, by managing key high-risk anthropogenic features such as industrial infrastructure and water developments.

Wet Gas Flow Rates Computation System for Unattended Operational Natural Gas Well Based on ARM

In order to measure the gas and liquid flow rates of the wet gas on line not separation, this paper develops a wet natural gas two-phase computation system, which accompanies with the dual throttling wet gas flow meter as a secondary instrument. This flow computation system is based on ARM9 embedded system with the Linux OS and is powered by a solar power system. A hardware and software platform of a secondary instrument working for the flow rates computation is constructed for unattended operational natural gas wells. The signal acquisitions of the pressure, differential pressure, temperature, and the calculation of two phase metering model have been actualized. In addition to the basic function, the system provides display, storage, and historical data inquiry of the instantaneous and accumulative flow rates, as well as the GPRS wireless communication. It has already been trial run at some unattended operational wellheads for the gas and liquid metering of the wet gas.