Investigation of Back Pressure Effects on Transient Gas Flow Through Porous Media via Laboratory Experiments and Numerical Simulation

2014 ◽  
Author(s):  
Xiaolei Liu ◽  
Akkharachai Limpasurat ◽  
Gioia Falcone ◽  
Catalin Teodoriu
Keyword(s):  
Steady State ◽  
Gas Flow ◽  
Laboratory Experiments ◽  
Transient Flow ◽  
Pressure Profile ◽  
Back Pressure ◽  
Pressure Effects ◽  
Gas Wells ◽  
Liquid Loading ◽  
Final Steady State

When developing a transient numerical reservoir simulator, it is important to consider the back pressure effects that waves propagating from one end of the porous medium will have on the temporal distribution of pore fluid pressure within the medium itself. Such waves can be triggered by changing boundary conditions at the interface between reservoir and wellbore. An example is given by the transient reservoir response following pressure fluctuations at the wellbore boundary for gas wells suffering from liquid loading. Laboratory experiments were performed using a modified Hassler cell to mimic the effect of varying downhole pressure on gas flow in the near-wellbore region of a reservoir. Gauges were attached along a sandstone core to monitor the pressure profile. The results of the experiments are shown in this paper. A numerical code for modelling transient flow in the near-wellbore region was run to mimic the experiments. The comparisons of simulations and laboratory test results are presented here, for the initial and final steady-state flowing conditions, and where the inlet pressure was maintained constant while initiating a transient pressure build up at the core outlet. The concept of the U-shaped pressure profile along the near-wellbore region of a reservoir under transient flow conditions, originally proposed by Zhang et al. [1], was experimentally and numerically reproduced for single-phase gas flow. This is due to a combination of inertia and compressibility effects, leading to the reservoir response not being instantaneous. The results suggest that, in two phase gas-liquid conditions, liquid re-injection could occur during liquid loading in gas wells. From the experimental results, the U-shaped curves were more obvious and of longer duration in the case of greater outlet pressure. The transition from the initial to the final steady state condition occurred rapidly in all the cases shown here, with the U-shaped pressure profile appearing only over a relatively short time (at the small scale and low pressures tested in this study).

The Need to Understand the Dynamic Interaction Between Wellbore and Reservoir in Liquid Loaded Gas Wells

2008 ◽  
Author(s):  
Fouad A. Solomon ◽  
Gioia Falcone ◽  
Catalin Teodoriu
Keyword(s):  
Oil And Gas ◽  
Transient Flow ◽  
Oil And Gas Industry ◽  
Dynamic Interaction ◽  
Back Pressure ◽  
Pressure Effects ◽  
Gas Wells ◽  
Liquid Loading ◽  
Dynamic Interactions ◽  
Model Liquid

Liquid loading in gas wells is a phenomenon where the liquid content of the well is sufficient to create a back pressure (usually dominated by gravitational pressure changes) which restricts, and in some cases even stops, the flow of gas from the reservoir. Liquid loading is an all too common problem in mature gas fields around the world. It is estimated that in the U.S.A. alone, at least 90% of the producing gas wells are operating in liquid loading regime. The phenomenon is more detrimental in tight wells than in prolific wells and it poses a serious problem in subsea tie-backs, where back pressure effects through the risers and the flowlines may have an important role. Such is the importance of liquid loading; the oil and gas industry has devoted a lot of attention to the alleviation of the problem using various measures. However, the fundamental understanding of the associated phenomena is still surprisingly weak. This applies not only to the flows in the wells, but also to how these flows interact with those in the reservoir. It is this latter dynamic interaction that has received the least attention by the industry. Reliable predictive models to link the well dynamics with the intermittent response of a reservoir, that is typical of liquid loading in gas wells, remain unavailable. This paper introduces the complexity of liquid loading and critically reviews recent attempts to model liquid loading and the dynamic interactions between reservoir and wellbore. The paper then illustrates the need for a better understanding of the transient flow phenomena taking place in the near-wellbore region of the reservoir. This includes re-injection of the heavier phase, a phenomenon that has yet to be proven by fluid mechanics.

Investigating the dynamics of gas hydrates in a gas dominant flow loop

2011 ◽  
Vol 51 (2) ◽  
pp. 734
Author(s):  
Yutaek Seo ◽  
Mauricio Di Lorenzo ◽  
Gerardo Sanchez-Soto
Keyword(s):  
Steady State ◽  
Gas Hydrates ◽  
Gas Hydrate ◽  
Gas Flow ◽  
Transient Flow ◽  
Hydrate Formation ◽  
Hydrodynamic Condition ◽  
Gas Pipelines ◽  
Flow Loop ◽  
Offshore Pipelines

Offshore pipelines transporting hydrocarbon fluids have to be operated with great care to avoid problems related to flow assurance. Of these possible problems, gas hydrate is dreaded as it poses the greatest risk of plugging offshore pipelines and other production systems. As the search for oil and natural gas goes into deeper and colder offshore fields, the strategies for gas hydrate mitigation are evolving to the management of hydrate risks rather than costly complete prevention. CSIRO has been developing technologies that will facilitate the production of Australian deepwater gas reserves. One of its research programs is a recently commissioned investigation into the dynamic behaviour of gas hydrates in gas pipelines using a pilot-scale 1 inch and 40 m long flow loop. This work will provide experimental results conducted in the flow loop, designed to investigate the hydrate formation characteristics in steady state and transient flow. For a given hydrodynamic condition in steady state flow, the formation and subsequent agglomeration and deposition of hydrate particles appear to occur more severely as the subcooling condition is increasing. Transient flow during a shut-in and restart operation represents a more complex scenario for hydrate formation. Although hydrates develop as a thin layer on the surface of water during the shut-in period, most of the water is quickly converted to hydrate upon restart, forming hydrate laden slurry that is transported through the pipeline by the gas flow. These results could provide valuable insights into the present operation of offshore gas pipelines.

Simulation of the Performance of the Venturi Scrubber for an Advanced Reactor Containment Venting Conditions

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Goel Paridhi ◽  
K. Nayak Arun
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Gas Flow ◽  
Pressure Profile ◽  
Absorption Efficiency ◽  
Severe Accident ◽  
Mitigation Measures ◽  
Liquid Loading ◽  
Venturi Scrubber ◽  
Iodine Absorption

Abstract Post Fukushima, nuclear plants are being retrofitted with severe accident mitigation measures. For attaining depressurization of the containment and mitigate the consequences of the release of the radioactivity to the environment during a severe accident condition, filtered containment venting systems (FCVS) are proposed to be installed in existing reactors and being designed for advanced reactors. The design of FCVS is particular to the reactor type. The FVCS configuration considered in this paper comprises of a manifold of venturi scrubber enclosed in a scrubber tank along with metal fiber filter and demister for an advanced Indian reactor. This study focuses on the assessment of the design of the venturi scrubber for the reactor conditions at which venting is carried out through a numerical model. The numerical model is first validated with experiments performed for prototypic conditions. The predicted pressure drop and the iodine absorption efficiency were found to be in good match with the experimental measurements. Subsequently, the model is implemented for predicting the hydrodynamics, i.e., pressure drop, droplet sizes and distribution, and iodine absorption for prototypic conditions. The hydrodynamics, i.e., pressure profile in the venturi scrubber showed a decrease in the converging section and in the throat section. The diverging section showed decrease in recovery of pressure with the decrease in gas flow because of the increased liquid loading to the scrubber. The iodine absorption efficiency showed a value of 92% for high gas velocity which decreased to 68% for the lowest gas flow rate.

An Attempt to Predict the Time Dependence of Well Deliverability in Gas Condensate Fields

1967 ◽  
Vol 7 (02) ◽  
pp. 113-124 ◽  
Author(s):  
M. Gondouin ◽  
R. Iffly ◽  
J. Husson
Keyword(s):  
Gas Flow ◽  
Empirical Equation ◽  
Radial Flow ◽  
Pore Space ◽  
Back Pressure ◽  
Gas Condensate ◽  
Reservoir Pressure ◽  
Gas Wells ◽  
Pressure Tests ◽  
C And N

Abstract A systematic variation of well deliverability, as reflected from isochronal back-pressure tests performed at regular intervals, has been observed in some gas condensate wells producing at high rates. The same effects have been obtained using a numerical model of gas and condensate flow which takes into account secondary gasoline deposited in the pore space as a result of pressure reduction, and nondarcy flow of gas in the vicinity of the wells. Matching calculated values with previous test results bas been possible, and future predictions have been obtained. An application of this method to the Hassi Er R'Mel gas-condensate field in Algeria is tentatively shown. Introduction Flow capacity of gas wells is generally derived from an analysis of back-pressure tests. The empirical equation q = C(Delta p)n used by Rawlins and Schellhardt can be derived rigorously assuming that steady-state radial flow of a dry gas of constant viscosity and compressibility is established during each flow period of the well tests. Furthermore, when Darcy's law applies in the entire flow region, the theory predicts that the exponent n is equal to 1. In low-permeability reservoirs, it was soon discovered that the time required to reach a stabilized flow often exceeded the duration of the flow periods normally available for testing wells. Consequently, transient gas flow had to be considered instead of the steady-state assumption previously used. This led to the isochronal testing procedure established by Cullender which has largely replaced conventional back-pressure testing. For dry gas fields, this method yields definite values of C and n equivalent to those of the empirical equation. These values should remain constant for each well as long as the permeability of the formation and the characteristics of the gas (viscosity and compressibility) do not change appreciably. This is the case when reservoir pressure remains close to the original value and when the formation near the wellbore remains free of plugging. Under those conditions, stabilized flow potential curves of gas wells can be established from a single sequence of isochronal flow and shut-in periods. An analysis of a pressure build-up following a longer production period provides additional data on the transmissivity (kh/mu) of the reservoir, and eventually on the drainage radius rd of the well, which can be related to the value of C so that future performance of the well can be predicted using the concepts developed by A. Houpeurt. At high How rates, Darcy's law no longer applies in the vicinity of the wellbore, and inertial effects in the high velocity gas flow introduce additional pressure drops. As a consequence, exponent n of the back-pressure tests becomes smaller than 1, and a slight curvature of the log-log plot of Delta p vs q can be predicted When going from very low to high rates of flow (Elenbaas and Katz). The effects of variations of viscosity and compressibility with pressure on the radial flow of dry gas in an infinite reservoir were taken into account by Jenkins and Aronofsky. Numerical solutions of the transient flow of an ideal gas in finite radial reservoirs were presented by Bruce, Peaceman, Rachford and Rice. In the case of gas condensate wells however the presence of gasoline in the pore space as soon as reservoir pressure is reduced below the dewpoint pressure further complicates the interpretation of flow tests so that the prediction of stabilized well performance becomes very difficult. Field observation shows that both C and n derived from isochronal tests vary in time, even when reservoir pressure has not changed appreciably. Such a variation cannot be attributed to any change of the gas characteristics, and must result from the effect of a gasoline saturation on the gas flow. SPEJ P. 113ˆ

Analytical Models for Liquid Loading in Multifractured Horizontal Gas Wells

SPE Journal ◽  
2016 ◽  
Vol 21 (02) ◽  
pp. 471-487 ◽  
Author(s):  
Juntai Shi ◽  
Zheng Sun ◽  
Xiangfang Li
Keyword(s):  
Flow Velocity ◽  
Gas Flow ◽  
Liquid Drop ◽  
Liquid Droplet ◽  
Shape Change ◽  
Analytical Models ◽  
Gas Wells ◽  
Gas Reservoirs ◽  
Liquid Loading ◽  
Gas Flow Velocity

Summary Liquid loading is a key issue in gas reservoirs with horizontal wells and multiple hydraulic fractures, especially for shale-gas reservoirs. Field results show that only 15–30% of the original fracturing fluid is recovered. Most liquid is trapped in the rock matrix near the fracture face and induced fractures. Water flowback from reservoir to wellbore and liquid loading from wellbore to surface are two main factors affecting the recovery of the original fracturing fluid. Significant efforts have been made to understand the effect of liquid loading on well performance, and some models have been proposed to describe the liquid loading. However, these models ignore the effect of liquid-drop size and its shape change with size. The falling liquid is nearly spherical in shape when its diameter is smaller than 2 mm, but when larger than 2 mm, it will change to be a half-hamburger in shape. Hence, ignoring the liquid-drop size and its shape change with size will lead to inaccurate calculations of the critical liquid-loading-flow rate. In this study, we conduct several groups of experiments to examine the liquid-droplet-shape change with liquid-droplet size in a gas-flow wellbore with different inclined angles. Similar to the falling liquid in air, larger liquid droplets are half-hamburger in shape (like the top half of the bun, flat on bottom and round on top). On the basis of this phenomenon, we propose analytical models to describe the critical liquid loading in vertical, slanted, and horizontal wellbores by considering the size and shape of liquid drops. Also, we validate this model by use of field data from the Daniudi gas field, and apply the proposed model to evaluate the liquid-loading problem in the Marcellus shale. Results show that the ratio of the liquid-drop height/width is a strong function of the liquid-drop width. Both the maximum and minimum ratios are determined: The maximum is unity, representing the shape of a sphere; the minimum is 0.3765; and the liquid drop is unstable when the ratio is less than 0.3765. In addition, the liquid drop with the minimum ratio is most easily loaded and produced from the vertical wellbore of gas wells. The key coefficient of B in the model of critical liquid-loading-flow velocity—vg = B[σ(ρl–ρg)/ρg2]0.25—is a function of the width of the liquid drop. The range of B is quantified as from 1.54 to 2.5. In the slanted wellbore of gas wells, the critical liquid-loading gas-flow velocity is related to the angle β, the slant angle, and the width of the liquid droplet. In the horizontal wellbore of gas wells, the critical liquid-loading gas-flow velocity is a function of the width of the liquid droplet. The models proposed in this work can accurately calculate the critical liquid-loading-flow rate for multifractured horizontal gas wells. This study can provide critical insights into the understanding of the liquid flowback and its effect on well productivity in gas reservoirs.

A New Model of Critical Liquid Carrying in Gas Wells

2012 ◽  
Vol 616-618 ◽  
pp. 730-736
Author(s):  
Rong He Liu ◽  
Ben Quan Zhang ◽  
Wen Guang Feng
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Spherical Shape ◽  
Gas Flow Rate ◽  
Gas Wells ◽  
Liquid Loading ◽  
Liquid Drops ◽  
New Model ◽  
Mist Flow ◽  
New Equation

Based on the Turner’s liquid-loading model for gas wells, combined with Liquid Membrane Breaking Theory and Law of energy Conservation, a new liquid-loading model for mist flow in wave shaped crushing mode for gas-liquid wells was put forward, and a new equation for critical liquid-loading gas flow rate estimation was derived. The results show that the lowest conditions for liquid loading is that most of liquid drops can continuously move upward in gas flow, and when radii of liquid drops are smaller than 1600μm, liquid drops in the wellbore are basically in spherical shape. The critical liquid-carrying gas flow rate, in gas wells, calculated with this new model, is more reasonable and accurate.

Sign in / Sign up

Export Citation Format

Share Document