Gascondensate fluids are termed retrograde because their behavior can be the reverse of. In reservoirs the dissolved gas is mainly methane from 10 scfstb at psi to 35 scfstb at 10 000 psi for gas water systems, and slightly less for wateroil systems. Increasing well productivity in gas condensate wells in qatars north field. Design of experiments introduction rich gas or retrograde condensate gas reservoir is a common type of hydrocarbon reservoir around the world. The south parsnorth dome field is a naturalgas condensate field located in the persian gulf. Table 2 shows data for three different examples of wet gas. According to the previous studies, the addition of some nitrogen causes a considerable increase in mixture dew. For the gas condensate used in the study, the liquid phase essentially drops out of vapor between 2300 psia and 2200 psia, as the plot suggests. The more recent models actually attempt a full dynamic integration. Determination of original gas condensate composition in. The liquid dropout curve assumes the two phases remain in contact with one another.
It is by far the worlds largest natural gas field, with ownership of the field shared between iran and qatar. A gascondensate reservoir is special in the sense that when the pressure decreases, instead of having gas evolution, we have liquid condensation. Shift factors3 are included to account for volume translation. Gas condensate and natural gasoline are, like naphtha, 1 readily flammable, 2 will evaporate quickly from. A drygas reservoir is defined as producing a single composition of gas that is constant in the reservoir, wellbore, and leaseseparation equipment throughout the life of a field. According to the international energy agency iea, the field holds an estimated 1,800 trillion cubic feet 51 trillion cubic metres of insitu natural gas and some 50 billion barrels 7. A commercial simulator was then used to carry out numerical reservoir simulation of fluid flow in the north field. Characterization of gas condensate reservoirs is a di. Analysis of gas condensate and its different fractions of. The rich gas drops out more condensate than the lean gas bottom leftt.
Appendix b includes some special physical and mathematical constants that are of particular interest in gas reservoir engineering. The first step of the study involved gathering north field reservoir data from previously published papers. For practical purposes a gas condensate reservoir with a gor of above 10,000 vv 50,000 scfstb can be treated as a wet gas. Phase diagram of a typical retrograde gas with line of isothermal reduction of reservoir pressure for a twocomponent methanebutane gas condensate.
A novel psolssvm model for predicting liquid rate of two phase flow. Fundamentals of gas reservoir engineering, volume 23 elsevier. Confined phase envelope of gascondensate systems in shale. The history matched simulations support a range of critical condensate saturations from 10% to 30%, in good agreement with published laboratory values. Understanding gascondensate reservoirs semantic scholar. However, calculation of hydrocarboninplace of a gascondensate reservoir is more complex because of the change from a single gaseous phase in the reservoir to two phases gas and condensate at the surface.
The compositional case optionally uses tabular kvalues versus p, rather than equation of state fugacitybased kvalues. Producing the gas to separator conditions creates a mixture of gas and condensed oil. Reservoir that yield natural gas can be classified into essential four categories, these are. This paper develops a novel approach to obtain initial gas condensate reservoir composition from gas and liquid compositions taken from. For gases with gor of above 20,000 vv 100,000 scfstb. Troll is a saturated reservoir with fairly uniform composition in the gas cap and in the oil. Treatment of variations of composition with depth in gascondensate reservoirs. Properties and analysis of gas condensate handbook of. Depending on reservoir temperature, this fluid would be defined as an oil or a gas. Table 1 gives the compositions of separator gas and liquid streams and other data used in making a recombined sample for analysis of reservoir fluid composition a cce using a visual cell furnishes the dewpoint of the reservoir fluid at reservoir temperature and the total volume of the reservoir fluid as a function of pressure. The analysis revealed that collected gas condensate contains more than 50% is motor spirit regular octanepetrol in the boiling range of 211450c, 23% is kerosene in the boiling range of 1402210c and 2425% is diesel in the boiling range of 1783350c.
The gas condensate separated from natural gas at reduced pressure andor temperature by reverse condensation is a colorless or slightly colored liquid of density 700800 kgm 3, which begins to boil at 3070c. Ding zhu condensate blockage negatively impacts large natural gas condensate reservoirs all over the world. Volatile oil and gas condensate reservoir fluid behavior. Dec 29, 2019 the ultimate output of the model is basically comprised of gor prediction and the compositions of the gas and condensate surface effluents. Treatment of variations of composition with depth in gascondensate. Craft and hawkins 1991 identified three types of oil and gas reservoirs based on their hydrocarbon fluid composition. The issues that must be addressed by analysis in a gas condensate reservoir are the variation of the condensate yield that will vary during the life of a reservoir and the manner in which the two. Typically, gas condensate contains hydrocarbons boiling up to c 8 fig. In this chapter, gas reservoirs have been divided into three groups.
The need for integration had been recognized earlier particularly for gas condensate reservoir, gas cycling processes, and volatile oil systems. Much of the 6,183 trillion cubic feet of worldwide gas reserves can be found in gas condensate reservoirs. The fluid selected for our study is a very rich gas condensate taken from cusiana field located 125 miles northeast of. Natural gas condensate encyclopedia article citizendium. In a retrograde gas condensate reservoir middle, temperature is below the cricon dentherm, causing oil to condense as pres sure decreases. Reservoir engineering focuses on the fundamental concepts related to the development of conventional and unconventional reservoirs and how these concepts are applied in the oil and gas industry to meet both economic and technical challenges. These conditions are favor able for the gascondensate mixture to be completely in the gaseous state in the reservoir. Pressure decline below the dew point pressure causes condensation to occur which creates a hydrocarbon liquid saturation in the reservoir. A gas condensate reservoir is special in the sense that when the pressure decreases, instead of having gas evolution, we have liquid condensation. The depletion of rich, gas condensate reservoirs to pressures significantly below the dew point is a topic of increasing interest as deeper, hotter hydrocarbon reservoirs are exploited. The algorithm is a valuable tool for the reservoir engineer who analyzes gas condensate reservoirs. Gas condensates are hydrocarbons in which conditions of temperature and pressure have resulted in the condensation of heavier hydrocarbons from the reservoir gas.
There are many condensate sources, and each has its own unique gas condensate composition. Compositional modeling of gascondensate reservoirs. A gascondensate reservoir can choke on its most valuable. Once an accurate model was obtained, the following three solutions to. To obtain the socalled blackoil pvt properties bo, bg, rs, and rv of gas condensates, this. Request pdf understanding gascondensate reservoirs the combination of fluid. Natural gas condensate is a lowboiling mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields if the raw gas temperature is reduced to below its hydrocarbon dew point, the liquids begin to condense out of the gas. Composition of gas condensate knowledge of the gasliquid ratlo and the gravity of the lcluid s not sufficient to describe the composi tion of gas condensate for all purposes. In reservoirs the dissolved gas is mainly methane from 10 scfstb at psi to 35 scfstb at 10 000 psi for gaswater systems, and slightly less for wateroil systems. Lean gas condensateleanlean gas condensate gas condensate rich gas condensaterichrich gas condensate gas condensate 0 0. Natural gas condensate sweet may contain variable amounts of benzene and nhexane. Two additional phasesa condensate gas and its condensate liquidwere added to an existing black oil model in order to simulate the behavior of a condensate gas cap over an oil zone.
Reservoir management requires a deep knowledge of the reservoir that can be achieved only through its characterization by a process of acquiring, processing and integrating several basic data. Simulation study of enhanced condensate recovery in a gas. Gas condensate composition and natural gasoline composition are monitored mainly by gas chromatography gc, and although most of the methods may have been developed for gasoline or naphtha, the applicability of the test methods to gas condensate. The compositional case optionally uses tabular kvalues versus p. A good understanding of how the gas condensate reservoirs vary in. Confined phase envelope of gascondensate systems in shale rocks. Sleipner is an example of an undersaturated gas condensate reservoir with relatively uniform composition. This book presents a comparison of different methods for generating pvt properties of volatile oil and gascondensate reservoir fluids determined that pvt properties generated with the whitson and torp method agree the best with full eos compositional simulation. Production with gor 100,000 scfbbl is commonly called lean or dry gas.
The simulation of horizontal wells with 14stage hydraulic fractures was conducted in a shale reservoir containing a wide spectrum of rock and fluid types, dry gas to gascondensate, and oil. Gas condensate is a hydrocarbon liquid stream separated from natural gas and consists of highermolecularweight hydrocarbons that exist in the reservoir as constituents of natural gas but which are recovered as liquids in separators, field facilities, or gasprocessing plants. In fact, in the early days of compositional reservoir simulation, a nondynamic integration of these two was the norm. The behavior of reservoir of a reservoir fluid during producing is determined by the shape of its. A dry gas reservoir is defined as producing a single composition of gas that is constant in the reservoir, wellbore, and leaseseparation equipment throughout the life of a field. When pressure decreases at reservoir temperature, a rich gas top leftt forms a higher percentage of liquid than a lean gas top rightt. In gascondensate reservoirs, a major challenge is to avoid the dropout of the heavier fractions, which represent the rich part of the gas, responsible for great part. The difficulty lies in the variation of the composition of the insitu fluid due to the accumulation of heavy. Pdf production performance of gas condensate reservoirs. It also affects distribution through the wettability of the reservoir rocks chapter 7. The depletion of gas condensate reservoirs to pressures below the dew point has been studied by reservoir engineers for many years. Higher salinity formation waters tend to contain less dissolved gas.
From a technical point of view, the various types of reservoirs can be defined by the location of the initial reservoir temperature and pressure with respect to the twophase gas and liquid envelope as commonly shown on pressuretemperature pt phase diagrams. Ula is an example of an undersaturated oil reservoir with relatively uniform composition. Changes in pressure and flow rate during well testing can alter petroleum composition and physical properties. This book is conflated based on the last scientific researches by authors and according to the last books and articles which are published in fundamentals of reservoirs engineering. The physical properties of gas condensate and natural gasoline depend on the types of hydrocarbon derivatives present in the liquids. Phase diagram of a typical retrograde gas with line of isothermal reduction of reservoir pressure for a twocomponent methanebutane gascondensate. However, calculation of hydrocarboninplace of a gas condensate reservoir is more complex because of the change from a single gaseous phase in the reservoir to two phases gas and condensate at the surface. Natural gas condensate sweet is extremely flammable and can cause eye, skin, gastrointestinal, and respiratory irritation as well as dizziness and loss of balance. This work describes a method for estimating reservoir fluid composition for gas condensates and volatile oils from readily available field data. Natural gas condensate article about natural gas condensate. Pdf experimental study of composition variation during flow of. Written in easy to understand language, the book provides valuable information regarding presentday tools, techniques, and technologies and explains best. L and v are the mole fractions of liquid and vapor, for each step of equilibrium of a constantcomposition expansion test.
Pdf unconventional shale oil and gascondensate reservoir. Accumulation of liquids in gascondensate reservoirs may lead to a vertical flow of liquid caused by density difference in the presence of gravity. Composition variation during flow of gascondensate wells. An oil exhibits a bubblepoint pressure at saturated conditions, while a gas condensate exhibits a dewpoint pressure at saturated conditions. We start with a singlephase gas reservoir fluid, of a known composition, at an initial reservoir pressure and temperature. Estimating reservoir composition for gas condensates and.
Understanding the behaviors of gas condensate reservoirs. Compositional numerical model a case study of hai thach moc tinh fields find, read. During wet gas reservoir life, the gasoil ratio does not change. Simulation study of enhanced condensate recovery in a gascondensate reservoir iranian journal of chemical engineering, vol.
An example of gas compressibility factor and condensategas ratio of a gas condensate system is presented in figure 4. Oseberg is an example of a saturatedundersaturated. The gascondensate content in gases of various deposits ranges from 12 to 700 cm 3 per 1 m 3 of gas. Figure 1 shows a pressuretemperature diagram for a specific reservoir fluid composition. Appendix a lists the commonly used units in gas reservoir engineering, along with their conversion factors. Compositional modeling of gascondensate reservoirsthe. Determination of original gas condensate composition. The composition of gas condensate is presented in the table 4. Fluid composition the composition of the reservoir fluid has an extremely important control on its pressurevolumetemperature properties, which define the relative volumes of each fluid in a reservoir. The field data were obtained from a middle east gascondensate reservoir and cover a wide range of flow rates and choke sizes. The expected character of the petroleum such as api gravity and gas to oil ratio and reservoir conditions such as pressure and temperature must be considered so that representative samples can be obtained. In certain cases, the assumption of fixed oil and gas composition is no longer valid. More serious health effects can occur if condensate is inhaled or swallowed. In addition, a twophase region exists between the bubble point and dew point lines.
Also during wet gas reservoir life, stocktank gravity of condensate liquid remains constant. Natural gas from shales ngs and from tight rocks are one of the most important fossil energy resource in this and next decade. In general, gas condensate has a specific gravity ranging from 0. The field data were obtained from a middle east gas condensate reservoir and cover a wide range of flow rates and choke sizes. The ultimate output of the model is basically comprised of gor prediction and the compositions of the gas and condensate surface effluents. Tran and others published production performance of gas condensate reservoirs.
The algorithm is a valuable tool for the reservoir engineer who analyzes gascondensate reservoirs. The development of gascondensate reservoirs by gas injection is treated in chapter 12. The reservoir fluid, its composition and phase behavior. Estimation of insitu compositions in lean gas condensate.
The simulation of horizontal wells with 14stage hydraulic fractures was conducted in a shale reservoir containing a wide spectrum of rock and fluid types, dry gas to gas condensate, and oil. Understanding gascondensate reservoirs request pdf. The producing gor initially remains constant until the reservoir pressure falls below the dew point and increases thereafter. Condensate and natural gas liquids frequently associated with a gas field gas the pressure and high temperatures in the deep underground gas reservoir means that some low boiling point hydrocarbon compounds which would be liquids at normal temperatures and pressures above the ground become gases under the ground. South parsnorth dome gascondensate field wikipedia. Providing practicing engineers critical information on all aspects of gas gathering, processing and transmission, this book examines natural gas energy costs and pricing with the aim of delivering. Most known retrograde gascondensate reservoirs are in the range of 3000 to 8000 psi and 200400. At discovery, these reservoirs are often in single phase. The development of gas condensate reservoirs by gas injection is treated in chapter 12. The condensate gas was assumed to contain vaporized liquid, and the condensed liquid contained dissolved gas. This synthetic reservoir model of a single layer homogenous reservoir was generated. Written in easy to understand language, the book provides valuable information regarding presentday.