Gas Production Loss Research Articles

Rationing of technical losses of gas and gas for own consumption at gas production enterprises

The article deals with the issues connected with rationing of gas production losses at oil-and-gas production enterprises. The evaluation of process losses is presented; the structure and system of their accounting are considered. Associated and natural gas losses breakdown is given by sources of their origin and trends of required gas for own consumption of oil and gas producing enterprises are classified. Based on generalized theoretical and practical material on the setting of norms for losses, a standard technique for process losses of gas and its own consumption has been developed. Norms of process losses and gas for own consumption were calculated based on the technique for nine OGPDs, two underground gas storages of the Azneft PU and eleven oil and gas operating companies. Structural constitution of process losses was analyzed at all these enterprises, a comprehensive benchmarking of loss rate was carried out, a flow diagram of standard own consumption of gas was constructed, and conclusions were drawn.

A systematic investigation into the flowback cleanup of hydraulic-fractured wells in unconventional gas plays

This paper conducts an extensive investigation into fracture cleanup efficiency by considering several pertinent parameters instantaneously over a wide practical range. Injection, shut-in and production stages of the fracturing operation were simulated for 32 sets consisting of 113,072 runs. To perform such a large number of simulation runs, a computer code was utilised to routinely read input data, implement the simulation runs and produce output data. In each set (which consists of 4096 runs), instantaneous impacts of twelve different parameters (i.e., fracture and matrix permeability, Brooks matrix capillary pressure (Pc) parameters, and Brooks-Corey relative permeability parameters) were investigated. To sample the domain of variables, full factorial experimental design (two-level FFS) was employed. The linear surface methodology was used to map the simulation output, which is the loss in gas production (GPL), compared to the clean case (i.e., 100% clean-up) after three production periods of 10, 30 and 365 days.The impact of various combinations of fracture fluid injection volume, fracture length, shut-in soaking time, matrix permeability variation range and drawdown on GPL were studied in different sets. Additionally, more simulation sets were performed to capture the impact of hysteresis, layering and mobile formation water on the clean-up efficiency.Results indicated that in line with some literature data, factors that controlled the mobility of FF inside the fracture had the most significant impact on cleanup efficiency. It was also noted that injecting high volumes of FF, into very tight formations significantly delayed clean-up and impaired gas production. The effect of varying other parameters such as extending soaking time or increasing pressure down in such a case delivered negligible GPL improvement. Introducing hysteresis made clean-up slightly faster in all production periods.The impact of the gravity segregation was discussed in this study. Considering the layered systems, it was indicated that in the top layer, the fracture mobility coefficients were more important than the ones in the bottom layer whist capillary pressure seems to become more important in deeper layers compared to the top layers.Additionally, a slower clean-up was observed for sets with larger initial water saturation compared to those cases with immobile water saturation due to the detrimental effect of mobile water on gas production. In some cases, with significantly high values of water saturation, using chemicals (which IFT reducing agents) to reduce Pc could reduce GPL and improve cleanup efficiency.These findings contribute to the further understanding of the fracture fluid cleanup process and provide practical guidelines to achieve economically successful hydraulic fracturing operations, which are popular but expensive for tight and ultra-tight reservoirs.

Maximizing fracture productivity in unconventional fields; analysis of post hydraulic fracturing flowback cleanup

Hydraulic fracturing, is a promising stimulation technique which is also known as hydrofracturing, hydrofracking and fracking. During the hydraulic fracturing (HF), the rock is cracked, i.e., fractured, by a high pressure injection of a fluid which is known as fracturing fluid (FF). The FF is mainly water, carrying suspended sand or another type of proppants into the well to initiate fractures in the reservoir rock, and consequently, hydrocarbon and FF will move towards the well more easily through fractures.Hydro-fracturing is extensively used to increase the well productivity index, particularly in unconventional, tight and ultra-tight reservoirs. This expensive procedure, though, sometimes fails to meet the production enhancement expectations. The most common explanations put forward for this reduced performance is fracture clean-up inefficiency of the fracturing fluid (FF).In this study, a parametric investigation of FF clean-up effectiveness of fractures was performed with 143360 simulations (in 35 different sets) including injection, shut-in and production stages. Because of the large number of simulation runs which was required, a computer code was utilised to routinely read input data, perform the simulation runs and produce output data. In each set (which consists of 4096 runs), instantaneous impacts of twelve different parameters (fracture and matrix permeability (i.e., Kf and Km) and capillary pressure (Pc), end points and exponents of gas and FF in the Brooks-Corey relative permeability correlation in both fracture and matrix) were investigated. To sample the domain of variables and to study the results, full factorial experimental design (two-level FFS) and linear surface methodology were used to describe the dependency of the loss in gas production, compared to the case there is no loss (i.e., 100% clean-up) to the related parameters at different production stages. The simulation results were examined by looking at the tornado charts of the response surface models, frequency of simulation runs with given Gas Production Loss, GPL, and saturation distribution maps of FF.Some of the results demonstrate that in general, factors that control the mobility of FF inside the fracture had the most significant impact on cleanup efficiency, which are inline with earlier works. However, it is also shown that in tight and ultratight sets, particularly when the applied pressure drawdown for the duration of production stage was small, the impact of fluid mobility within the matrix on gas production loss was more noticeable, i.e., it is crucial how fluids flow inside the matrix rather than how fast fracture is cleaned. In lower permeability matrix, in general, more gas production loss was detected and clean-up was slower. The impact of matrix capillary pressure (Pc) on GPL minimisation was stronger when pressure drawdown was small and/or shut-in time was prolonged. As the formation becomes tighter, this observation was more pronounced, in other words, for such formations, the impact of a change in pressure drawdown and/or shut-in time on Pc and GPL was more noticeable.Additionally, the results showed that as the length of the fracture reduced the impact of fracture pertinent parameters (i.e., fracture permeability and fluid (gas and FF) mobility pertinent parameters of Corey correlation in the fracture) on GPL reduced and the impact of those pertinent parameters in the matrix on GPL increased. The impact of Pc on minimising GPL is less noticeable in shorter fractures and vice versa. As the length of fracture reduced, quicker fracture clean-up was detected compared to those for longer fracture.These discoveries help us to better understand the hydraulic fracturing process and can be used to settle issues regarding the performance of hydraulic fracturing and to improve the design of costly hydro-fracturing operations.

Decision matrix for liquid loading in gas wells for cost/benefit analyses of lifting options

Liquid loading in gas wells is a multiphase flow phenomenon where the liquid content of the well creates back pressure that restricts, and in some cases even stops, the flow of gas from the reservoir. It is estimated that 90% of the producing gas wells in the U.S. are operating in liquid loading regime. Field-proven solutions already exist to reduce the loss of gas production when liquid loading begins to occur. However, whether or not the chosen remedy is technically feasible and cost effective will depend on the field's location, export route capacity and the operator's experience. Although there are literature reviews available that describe the possible solutions to liquid loading problems in gas wells, no tool currently exists which is capable of helping an operator select the best remedial option for a specific field case. The selection of the best remedial technique and the timeframe within which the remedial action is undertaken are critical to a project's profitability. This paper describes a newly developed decision matrix to screen the possible remedial options available to the operator. The matrix not only provides a critical evaluation of technical solutions to the problem of liquid loading in gas wells vis-à-vis the existing technical and economic constraints, but also serves as a quick screening tool for the selection of production optimization strategies. In its current state of development, the tool consists of an assessment algorithm used in conjunction with a decision tree. Being a data mining technique, the decision tree allows rapid subdivision of large initial data sets into successively smaller sets by a series of decision rules, which are based on information available in the public domain. The effectiveness of the matrix is now ready to be tested against real field data sets.

Fundamental Surfactant Properties of Foamers for Increasing Gas Production

In natural gas wells, gas production decreases due to the decline of reservoir pressure. The cause of this loss of gas production is liquid loading that occurs when water and condensate enter and remain in the bottom of the well. Foaming agents are frequently used to aid in the unloading of water and condensate accumulated in the production tubing. Fundamental surfactant properties of foamers have been measured and these have been successfully correlated to unloading performance. This provides a fundamental understanding of how foamers work and provides a rapid evaluation technique.

Viscosity predictions of the slag composition of gasified coal, utilizing FactSage equilibrium modelling

Agglomeration of ash particles provides the desired porosity of the ash bed for adequate agent (steam and oxygen) flow and distribution, whereas excessive slagging inside the gasifier can cause channel burning, pressure drop problems or unstable operation, resulting in cut backs on gasifier load, which implies a direct loss in gas production. The ash flow temperature (AFT) is one property that specifically gives more information on the suitability of a coal source for combustion or gasification purposes. However, normal AFT analyses give an average flow property and do not indicate exactly at what temperature the first melt/slag is occurring or what the properties of the slag is at a specific temperature. Operating experience indicates that even when the gasifiers are operated at temperatures above the flow temperature as given by AFT analysis, a low percentage of slag is formed. In this study, the focus will be on the application of viscosity determinations together with FactSage modelling. Conventional AFT analyses take the bulk chemical composition of the mineral phase into account, and does not differentiate between the composition in the slag–liquid phase and the composition of the crystalline phase. It is therefore important to describe the viscosity of not only the completely molten phase, but also the partly crystallised slag and liquid portion. The combination of viscosity predictions together with FactSage modelling will result in viscosity predictions of the actual liquid component, rather than just an average or pseudo-viscosity prediction of the total mineral system at a specific temperature. Based on the fact that the Urbain model assumes the composition as 100% liquid or molten, which is not the case for example during fixed bed gasification where the mineral structure is of a heterogeneous nature with partial melting and crystalline material, viscosity predictions of the slag or molten portion can be more accurately determined by using the FactSage results. The viscosities, as determined from specific slag compositions at specific temperatures between 1000 °C and 1250 °C, differ from the average viscosity prediction and is highly likely to be a more accurate prediction of the slag viscosity than just based on the average mineral composition. The viscosity of the actual slag composition also remains fairly constant up to temperatures >1200 °C. This can also be related back to the initial deformation temperature onset of the coal, where the slag properties are cumulative enough for the onset of deformation to start. The specific decrease of the viscosity at the temperature between 1200 °C and 1250 °C correlates with the slag formation trend as obtained with FactSage modelling. During the gasification process the viscosity of the slag portion decreases to ±3.5 cp, which is on the border between a weak deposit and strong deposit. With increasing temperature above 1250 °C, for this specific coal source the viscosity moved into the strong deposit region. After the gasification zone, the viscosity increased again as the material crystallised in the combustion process. For a specific coal source, the viscosity of the slag portion can thus be calculated. The major source of glass is derived from included minerals in carbon rich particles. It is clear that a focus on the modification of the unclassified/amorphous phase, to increase the viscosity (decrease slag formation or have a higher concentration of crystalline phases) at a certain temperature, is important. An AFT analyses only supplies information on the temperature where a mass of material, enough to deform the structure of the cone, starts to slag and does not give information on the properties of the slag below that point. The use of viscosity predictions together with FactSage modelling supplies a better understanding of slag and ash properties at specific temperatures.

Carbon/Nitrogen Ratio and Anaerobic Digestion of Swine Waste

ABSTRACT THE greatest volume of methane production was observed in digesters operating on a sub-strate of high carbon/nitrogen (C/N) ratio. How-ever, these digesters tended to be unstable ecologically and operated on the verge of failure. Digesters operated on a low C/N ratio (high nitrogen) substrate, although exhibiting lower gas production, were seen to become highly buffered and more stable. The low C/N digesters, because of their stability, were better able to adjust to increases in organic loading. The C/N range of 15.5/1 to 19/1 was found to be the optimum range in terms of maximum methane production based on variation in loading rates. Maximum gas production (690 mL CH4/g organic carbon loaded) occurred at a loading rate of 2.24 g volatile solids (VS)/L/day and a C/N ratio of 19/1. Due to unstable operating conditions observed at high C/N ratios, it is suggested that a C/N ratio of 16/1 may provide more operational stability with minimum loss in gas production. This corresponds to a 55 to 60 percent reduction in total organic carbon (TOC).