EMPIRICAL CORRELATION OF OIL EFFECTIVE PERMEABILITY AS A FUNCTION OF PRESSURE.
A poor description of the reservoir characteristics usually poses a unique problem in exploration and production there by leading to poor development and management of a reservoir field to yield optimum profit required. An accurate description is thus a vital key to an improved field development planning and management. This study illustrates how an integration of empirically determine oil effective permeability data was correlated as a function of average reservoir pressure. This is to provide the reservoir engineer with another tool to help him appreciate the importance of empirically determined data in estimating some reservoir properties during oil field planning, development and management to ensure optimum production from the fields.
Of all the formation parameters that petroleum Engineers use , permeability is one of the most important. Oil and Gas use both accurate and approximate permeability values. These values frequently are compared and correlated which are then used to make important conclusions about formation flow potential and for various aspect of reservoir management and development.
Rock formation permeability is one important flow parameter associated with subsurface production and injection .Its importance is reflected by the number of available technique (well-log evaluation, core measurements and well testing ) typically used to estimate it. The literature is full of comparison and correlations of permeability from these sources which are used to make important conclusions without proper regard to the interrelationship among them.
Permeability estimates by individuals techniques within the various permeability
sources can vary with the state of rock (in –Situ Environment), Fluid Saturation distribution flow direction etc. Correlation determines the degree of linear relationship between two variables at a time. Oil effective permeability is correlated as a function of pressure because some relationship exist between them and is found when a change in pressure result in a change in the oil permeability
value of the reservoir. Hence in this project topic titled Empirical Correlation of oil effective permeability, a comprehensive relationship between the two variables will be shown and new values will be predicted as well. This paper reviews the commercial available permeability estimation techniques and discusses the important factors that illustrate their interrelationships which allow meaningful permeability comparisons and correlations.
1.1 STATEMENT OF THE PROBLEM
Over the years, Petroleum Production Engineers has been troubled with many problems of which its effects or outcomes gave a poor analysis of reservoir production that generally leads to financial loss and time particularly. An inadequate analysis and understanding of a particular reservoir unfavorably affects the overall success of petroleum production. A reservoir engineers generally have the greatest claim on the use of such data, they are also quite valuable to drilling and production specialist. In many cases, the laboratory analysis to get an accurate and more appropriate permeability (most especially the oil effective permeability) may never be available because of economic reasons.
Reservoir rock properties can be examined through the following ways
1) Quality check laboratory analysis
2) Inability to obtain a representative sample during core analysis
3) Sample volume is sufficient to obtain a complete analysis
4) Estimating the potential production rate of a reserve found in exploration prospect
5) Error in laboratory analysis
From the problems above , there is need for generating empirical correlation to be used . This is due to the complications and complexities of formations which vary with location or places.
1.2 OBJECTIVES OF THE STUDY
The principal aim of carrying out this project work and research involved is to investigate the effects of pressure on the computation of oil effective permeability for Niger Delta reservoirs which are usually sandstone formation. In addition to experimentally measured properties of the reservoir rock, it is necessary for a
petroleum engineer to determine these properties from empirically derived
correlation. Therefore this work seeks to achieve the following;
⦁ To show establish the relationship between oil effective permeability and pressure
⦁ To show the trend in the relationship between the oil effective permeability and pressure data
⦁ To formulate suitable empirical equation using the oil effective permeability and average reservoir pressure data of a field located in Niger Delta.
⦁ To determine the nature of the relationship between the two variables that is if it a positive, negative or zero correlation.
⦁ To determine the correlation coefficient which measures the goodness of fit of the line of regression
1.3 SIGNIFICANCE OF THE STUDY:
There is usually great margin of error when oil effective permeability values are predicted without pressure and saturation consideration. Therefore this work seeks to provide a correlation that will enable the engineer predict oil effective permeability value when given pressure values from well test analysis knowing that the nature and properties of the reservoir does not change. Since production
rate is a function of oil effective permeability, its determination will enable the engineer to predict the production rate of the producing well therefore helps in adequate planning. The correlation will quickly offer the engineer a guide or tool of what the oil effective permeability value will be like at any given pressure which will aid in the planning stage for the optimum design of the well and selection of down hole completion and surface facilities. This will enhance adequate planning for optimum production of the well. This project work is essential as it exposes the relevance of a higher accuracy in making reservoir calculation as it affects production. Also with the knowledge of the correlated oil effective permeability value, viscosity, pore geometry, wettability, fluid distribution and saturation history which are function of oil effective permeability values can be determined and are relevance for the reservoir study. It is expected that the correlation will be useful in saving the cost and time expended in generating oil effective permeability values through laboratory analysis of the core samples.
1.4 SCOPE OF STUDY
As a result of the stringent measures in getting data from multinationals and limitation in time for this project work the result was based on the data collected from Niger Delta field. Also this work is restricted to the assessment of the effect of pressure on oil effective permeability not putting general consideration effect of
other reservoir petro physical properties. The new empirical correlation developed
is from the data gotten from oil producing well in Niger Delta. Also minimal effect
of errors that could result when taking the readings is evident in the correlation.
From the findings of this project work it becomes obvious that
⦁ In any reservoir Engineering calculation and prediction ,we should not neglect correlation technique.
⦁ Oil effective permeability value cannot be predicted without considering the average reservoir pressure which is directly affected by the saturation of the fluids in the reservoir.
⦁ Empirical data are one of the greatest assets petroleum engineer has in studying the reservoir and its properties.
⦁ Correlation technique is economically important because the time and money spent in carrying out other methods of determining the oil effective permeability value of a particular reservoir is minimized to a great extent.
⦁ Diversities in regression types helps to determine the actual trend two data variables has.
Based on the results obtained in this study, the following recommendations are
⦁ In analysis of a reservoir properties such prediction of oil effective permeability value as found in this project work, empirical data should never be neglected
⦁ Pressure effect on oil effective permeability cannot be accurately studied and correlated without considering the saturation of that fluid and other properties in the reservoir..