Essay on PVT Analysis for Reservoir Engineering Purposes

To determine the features and behavior of reservoir fluid under diverse conditions, we investigate the Pressure, volume, and temperature (PVT). The varied conditions include pressure, volumes, and temperature. The estimation of the amount of crude oil and gas, calculation of the flow properties of the reservoir fluids, optimization of the liquid recovery, availing of the details about pressure maintenance are often the essential objectives of the analysis. Oil service organizations undertake PVT analysis to provide near precise information data that helps in making qualitative engineering decisions. The report has made it simple to appreciate the complex behavior of reservoir fluids. It is well known that engineers collect surface gas and oil samples from the well sites to conduct these studies. At that point, the researchers utilize an ISCS integrated instrument called a capillary viscometer system to determine the properties.

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Applications of PVT Analysis

The PVT analysis is useful in the provision of the results for reservoir engineering purposes. It also supports the design and optimization of procedures and equipment. The analysis helps the engineers to maximize the hydrocarbon recovery at a cheaper cost. In this manner, therefore, using the ideal gas law, (PV= nRT), one can compute the PVT analysis. Additionally, the estimated values can also help in establishing the reservoir pressure and the compressibility feature of the fluid.

Type of Tests Performed in PVT Analysis

Engineers use various experimental methods to perform PVT analysis. One of the first steps they conduct is the multistage separator test on oil samples. Researchers undertake this test mainly to find a basis for converting differential liberation information from a residual oil to a stock-tank oil basis. The engineers carry out many separator tests to come up with the separator conditions that maximize stock-tank oil production. This test involves two or three stages of separation, with the last phase being at atmospheric pressure and near-ambient temperature of 15 to 250C. Thereafter, the engineers use the constant composition expansion (CCE) experiment to distinguish the bubble point pressure, the undersaturated oil density, the isothermal oil compressibility, and the two-phase volumetric behavior at pressures below the bubble point. The last stage of the test is the constant volume depletion (CVD) experiment. It provides the volumetric and compositional statistics for gas condensate that a deposit produces because of pressure reduction. It is important to note that while carrying out this experiment, the reservoir temperature must be constant.Multi stage separator test

A multi stage separator is a machine which functions to simulate a full-scale field separation unit. To determine the optimum field separator condition, there is need to calculate the changes in gas-oil ratio, and formation volume factor with changes in separator temperature and pressure. It is worth noting that the test generally takes place at several separator pressures. This test is usually carried out to provide a guideline for changing data from residual oil to stored oil criteria.

The essential information obtained from the tests include the following parameters:

Solution gas-oil ratio

Formation volume factor

Separator volume factor

The benefits of the trial are:

Accurate measurement of liquid and gas volume

Efficient stirring operation of the test fluid

Equilibrium condition are fast to attain

Viscosity test

The universal accepted definition of Viscosity is the measure of a fluids ability to resist to flow. It is one of the most important fluid properties, and that is because of its vital role in the petroleum industry. Any slight changes in viscosity can have a significant impact on the properties of petroleum fluids.

As is the case with the petroleum industry, the viscosity of crude oil generally affects the pumping procedure of crude oil from the ground. The researchers must calibrate the Viscometer to compute viscosity. This happens in the same time viscosity standards used to determine the viscometer constant [4]. Gathering data using viscosity test is important because it can be efficient in procedures such as lubricating oil and designing pipeline elements.

The following are the several ways to measure viscosity:

Capillary Viscometer

Zahn Cup

Falling Sphere Viscometer

Vibrational Viscometer

Rotational Viscometer

Constant composition expansion test (CCE)

To get a fluid sample at an earlier stage in the life of a field with some degree of accuracy from the composition, engineers undertake the constant composition expansion tests. Furthermore, to show the pressure volume relations of these hydrocarbon systems, the performance of the tests on crude oil or gas condensate are necessary [5].

The performance of the test to obtain the following properties:

Compressibility factors of the gas

Saturation pressure (bubble-point or dew-point pressure)

Total hydrocarbon volume as a function of pressure

Isothermal compressibility coefficients of the single-phase fluid more than saturation pressure

Highly volatile oils do not show a resemblance of discontinuity in its volumetric behavior at the dew-point pressure. It is important to note that while carrying out this experiment, the reservoir temperature must be constant.

Compositional Analysis of a Separator Liquid

Compositional analysis alludes to the estimation of the distribution of hydrocarbons and other elements present in oil and gas samples. Reservoir engineers use current chromatography methods to investigate samples to establish the breakdown of the elements in the sample. Compositional analysis is helpful in evaluating the quality of samples and aids to discern reservoir continuity and investigate leakage. The liquid analysis is between C1 to C35 plus C36 + to accomplish accurate data from the separator liquid. From the reservoir, we extract a liquid specimen to undergo studies related to knowing compositions of the reservoir. The aim of this study is to analyze the fluid sample to estimate hydrocarbon properties such as oil type, mole percentage and viscosity. Gathering data using viscosity test is important because it can be efficient in procedures such as lubricating oil and designing pipeline elements.

Gas chromatography is one of the common compositional analysis method used by engineers. In the method mentioned, a researcher heats a hydrocarbon until it vaporizes. An inert carrier gas then helps in distribution through adsorption porous material.

To identify the various compounds, researchers use flame ionization detector and in some cases, they use thermal conductivity detector. In the flame ionization detector method, the compounds are ionizing because of air and hydrogen burning. As the chromatography reaches its maximum, the difference in conductivity of the flame, proportions of electrons and ions are visible. For thermal conductivity detector, it measures the unique data rates at which the compounds give out the heat. Oil service organizations undertake PVT analysis to provide near precise information data that helps in making qualitative engineering decisions