Jinzhou Zhao

The Modeling of Sulfur Deposition Damage in the Presence of Natural Fracture

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.

Distribution of sulfur deposition near a wellbore in a sour gas reservoir

Elemental sulfur precipitates from sour gas when reservoir pressure and temperature decrease. Sulfur deposition in a formation may significantly reduce the inflow performance of sour gas wells. This paper develops a micro-mechanical migration model and experiments which describe the law of sulfur precipitation, plugging and distribution near a wellbore. Based on the analysis of the sulfur deposition law and micro-mechanical migration theory, elemental sulfur mechanical models in pores are presented. The critical velocity of sulfur is calculated and the rule of precipitated sulfur distribution near a wellbore is deduced. Reservoir cores and supersaturated sour gas are utilized to observe sulfur precipitation and plugging in sulfur damage experiments, and the main influential factor is analysed. According to the models and experimental results, precipitated sulfur can decrease reservoir permeability. The liquid bridge force is the most important factor to affect reservoir permeability due to sulfur deposition. Precipitated sulfur cannot be carried away from pores if the liquid bridge force is considered; the critical velocity increases as the diameter of the sulfur particles increases, which may cause serious formation damage. Moreover, it can be seen from the results that the biggest volume of sulfur deposition does not occur at the bottom but near the bottom of a borehole. These results can be used to describe the profile of dynamic sulfur deposition and help a reservoir engineer to develop a plan for removing the sulfur near a wellbore.

A Deliverability Equation in the Presence of Sulfur Deposition

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.

Notice of Retraction The research of sour gas reservoir damage mechanism

Sulfur deposition damage is one of the most important problems in sour gas reservoir development. With decreasing pressure and temperature near bore zones, solid elemental sulfur may deposit and block pore. Whats worse, it reduces the inflow performance of sour-gas wells. Based on the comprehensive analysis of deposit and block process, solid elemental sulfur motional and mechanical model were established with irreducible water considered. The results indicated that precipitated solid elemental sulfur did not move a long time in pore; they could in-suit deposit. Irreducible water plays an important role in sulfur deposition. The former precipitated solid blocked pore and the latter solid could be carried if gas velocity was big enough.

Productivity model of horizontal wells in a sour gas reservoir

ABSTRACT The utilization of a horizontal well has a great significance in the development of sour gas reservoir. The accurate prediction of the productivity of horizontal well will become more and more important in developing sour gas reservoir. In this paper, the effect of sulfur deposition on permeability is considered and a productivity prediction formula of the horizontal well is established. The effects of the length of horizontal well, the effective thickness of the reservoir, elemental sulfur deposition, and reservoir heterogeneity on productivity are analyzed and calculated. The theoretical results show that elemental sulfur disposition and the heterogeneity are the most important factors. According to the field case, the calculating results of improved Joshi’s equation approaches the real productivity, which means that it could be used to predict the productivity of horizontal well at initial stage during sour gas reservoir development. The results can be used as a reference for the development of similar sour gas reservoir.

A Material Balance Equation for a Sour Gas Reservoir

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.

Modeling of Sulfur Deposition Damage in the Presence of Irreducible Water

Abstract 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.