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The gas reservoir with high content of H2S is a special type of reservoir. With the decreasing of temperature and pressure, elemental sulfur may precipitate and block pore. The conventional material balance equation of common gas reservoir takes no account of the sulfur deposition. It is difficult to scientifically describe the performance of sour gas reservoir. Mol balance principle is used to establish material balance equation in sour gas reservoir. The modified material balance equation can be used to analyze the effects of deposited sulfur on original gas in place. For the different types of gas reservoir, such as constant-volume gas reservoir and water invasion gas reservoir, the material balance equation with high content of H2S is deduced and an example is presented to compare it with the conventional volume balance equation. This new model improves sour gas-engineering theory. [ABSTRACT FROM PUBLISHER]

Four typical crude oil samples collected from the Junggar Basin of northwest China were analyzed by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) under different experimental conditions, which include normal phase column system (nonpolar × polar) and reversed phase column system (polar × nonpolar). A comparative study was conducted on the general chromatogram features, and chromatogram features of saturate and aromatic hydrocarbons. Analytical results show that the normal phase (NP) column system has higher resolution for the identification of high molecular weight polycyoalkanes and polycyclic aromatic hydrocarbons, while the reverse phase (RP) column system has higher separation on the saturate hydrocarbons, especially on medium-low molecular weight iso-alkanes and cycloalkanes. In addition, the RP system can also meet the separation requirements of aromatic compounds, by the extraction of diverse organic compounds by characteristic ions. Therefore, the RP system has special advantages in the analysis of medium-low molecular weight hydrocarbon compounds in crude oil, and can be applied more widely in the future besides the presently common use of the NP system. [ABSTRACT FROM PUBLISHER]

Precipitated elemental sulfur may block pores, decrease gas flow, and affect sour gas well production if elemental sulfur cannot be carried by gas. A percolation model in the presence of sulfur deposition was analyzed under pseudo-steady state flow. On the basis of fundamental filtration theory, a composite deliverability test model was established to identify the effect of deposited sulfur on open-flow capacity and additional skin. A group of field case was used to calculate and analyze the effect of sulfur deposition on deliverability equation. The results show that gas flow capacity decreases as sulfur saturation rises, while open-flow capacity decreases as damaged radius increases. Also the more volume of deposited sulfur there is, the larger the additional skin is, and the more serious the damage to the reservoir is. [ABSTRACT FROM AUTHOR]

Gas mixture hydrates were quiescently produced from sodium dodecyl sulfate solutions of 20 ppm, 50 ppm, and 300 ppm to examine the potential for natural gas storage. Owing to the presence of C2H6and C3H8, the concentration of 20 ppm is sufficient to promote the hydrate formation, although higher concentrations are better. The porous hydrate trapping more free water shows better microwave absorption and a higher decomposition rate. While conducting the work, pre-depressurization may weaken the water activity by forming ice. [ABSTRACT FROM AUTHOR]

The authors present a rigorous method to analyze and interpret production rate and pressure data of low-permeability gas wells using type curves. The method is based on the type curve analysis method presented by Blasingame et al. (1991), but imports the wellbore storage coefficient, which influences the flow behavior of low-permeability gas wells significantly, for the first time. This work fills a significant void in the inventory of decline curve type curves, and the method is applicable to production analysis for cases taken from low-permeability gas wells. [ABSTRACT FROM AUTHOR]

With the decreasing of temperature and pressure near the wellbore area, elemental sulfur may precipitate in a sour gas reservoir. In order to acquire prediction and management of sulfur deposition, a carbonate sour gas reservoir damage model was established in the presence of natural fracture. The effects of formation parameters to gas limited production time are analyzed. The results show that when pressure is lower than saturation pressure, gas limited production time goes up with fracture aperture and height increasing, because the reservoir can accommodate more precipitated sulfur. The bigger production rate is, the faster pressure drop is and the quicker sulfur precipitates. [ABSTRACT FROM PUBLISHER]

For extra-low permeability sandstone reservoirs, traditional well test analysis techniques are always limited by wellbore storage coefficient and the low flow velocity in the porous media. Results derived using traditional well test analysis techniques are meaningless or useless. A deconvolution method based on the newly robust solution algorithms is applied for extra-low permeability sandstone reservoirs. Deconvolution codes were developed based on von Schroeter deconvolution algorithm and Levitan deconvolution algorithm. Though the study is based on synthetic cases and a field case, it is proved that the deconvolution algorithm works well in well test analysis of extra-low permeability sandstone reservoirs. [ABSTRACT FROM AUTHOR]

Low-permeability reservoirs have attracted increased attention from most oil companies due to increased demand and limited reserves in conventional reservoirs. Most scholars agree that worldwide hydrocarbon production decline from conventional reservoirs will be compensated for by the development of low-permeability reservoirs to satisfy growing demand. During the production life cycle of a low-permeability reservoir, permeability at any given location may change in response to the change of stress due to depressurization. Waterflooding is an important method used to develop low-permeability oil reservoirs. Therefore, it is necessary to study whether and how a stress state change can affect formation permeability. However, it is seldom seen the relevant research and report. This article presents a laboratory procedure to simulate the stress state change of ultra-low-permeability formation during injection and production applying cores from Changqing oilfield and evaluate the effect of stress on formation permeability under reservoir conditions using brine as the fluid medium. This work focuses on how formation permeability changes with stress change during injection and drawdown and discusses the difference in permeability change between injection and production. The analysis is not only on the basis of selecting zero pore pressure but also in situ pressure as the starting point; that is, a reference point. The results indicate that reservoir permeability changes during both drawdown and injection are caused by stress variation. Microcracks are the main factor resulting in this permeability change. This experimental method simulated formation stress state and flow behavior as truly. The results are meaningful for analyzing oil well production and reservoir development for ultra-low-permeability reservoir. [ABSTRACT FROM PUBLISHER]

With the decreasing of pressure and temperature, elemental sulfur may deposit and cause a decline in reservoir permeability. In this work, an elemental sulfur agglomeration mechanism and the effect of irreducible water on agglomeration were analyzed. A prediction model on sulfur deposition in the presence of irreducible water was proposed based on non-Darcy flow. The result shows that sulfur deposition damage mainly occurs near the wellbore, and irreducible water has a direct effect on sulfur particle agglomeration. When reservoir pressure is lower than the saturation pressure of elemental sulfur, precipitated sulfur block pore and decrease permeability, higher saturation degree of irreducible water lead to plug seriously, gas limited production time become shorter when non-Darcy flow is considered and productivity decline velocity become more quickly. [ABSTRACT FROM AUTHOR]

Acid fracturing is widely used as an effective reconstruction measure in sour gas reservoirs, but sulfur and ferrous sulfide plugging are still problems in reservoir secondary damage. In order to simulate reservoir damage in the presence of ferric ion in residual acid, an artificial core with ferric ion and supersaturated natural sour gas was adopted as a sample. A depletion-type damage experiment was carried out to observe sulfur precipitation and plugging in the core. The results show that core color became dark and weight was increased. Permeability decreased with increased time and the decreasing trend was steep at the beginning and then down to smooth rate slowly. Trace pyrite was discovered using X-diffraction. Severe damage was formed by sulfur deposition in the presence of ferric ion. [ABSTRACT FROM AUTHOR]