scholarly works
Permanent URI for this collectionhttps://repository.ui.edu.ng/handle/123456789/564
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Item A type curve approach to qualitative description of reservoir fluids(Society of Petroleum Engineers, 1993) Isehunwa, O. S.; Falade, G. K.Qualitative description of reservoir fluids is normally based on such parameters as saturation pressure, gas in solution, viscosity and density. Most Engineers ignore compositional data unless when phase behavior predictions or compositional simulation are to be undertaken. This work describes a simple, quick method of qualitative reservoir crude assessment, using the well known Type Curve matching techniques with fluid compositional data. The method is demonstrated for some Niger Delta reservoir crudes, and shown to be useful in checking the validity of laboratory PVT results in cases where there are disagreements between the experimental and observed (field) values of saturation pressure. Volatile crudes and condensates can also he readily identified. It. would appear that the method can be applied regionally, as well as locally (in-field) as an aid in reservoir-to-reservoir fluid correlation. It can also help to ide1ltify non-equilibrium fluid distribution in. large, thick, or segmented reservoirs.Item Improved characterization of heptanes-plus fractions of light crudes(Society of Petroleum Engineers, 2007) Isehunwa, O. S.; Falade, G. K.Heptanes plus fractions have strong effects on the physical properties and phase behaviour of petroleum fluids. It is therefore very important to properly characterize plus fractions. A step to achieving improved characterization is to obtain more realistic molecular weights. Most of the current methods of heptanes plus characterization assume their molecular weights are accurate. However, what is commonly measured in the laboratory is the molecular weight of the complete fluid; the molecular weight of the heptanes plus fraction is then estimated using Kay's mixing rule. Unfortunately, physical properties like molecular weight obtained using 'equivalent fluid' principles by mixing pure components, do not give the same values with actual measurements. Therefore, while a very accurate estimate of the molecular weight of a reservoir oil could be available, that of the heavy fractions, which is 'inferred' could be unreliable, because of the mixing rule. A simple technique has been formulated to achieve improved characterization of petroleum fluids and the heavy fractions. We suggest fine tuning' Kay's mixing rule in order to achieve a match between actual measured molecular weight and the 'equivalent fluid'. Experimental data from over 400 PVT reports from over 100 fields in the Niger Delta were collected and studied A correlation was established between oil gravity and molecular weight and compared with other commonly used correlations. Statistical error analysis was undertaken. Heptanes plus molecular weights which were generally estimated using Kay's mixing rule were found to be generally high and hence fine tuned using a simple technique. The results of this study show that the well-known Cragoe's and Standing correlations gave absolute average deviation of 126.8 and 53.3 respectively for light crudes, compared to 2.5 obtained in this study Furthermore, better description of heavy fractions was achieved with more accurate molecular weight. It is concluded that the proposed technique perhaps provides a theoretical basis for the usual 'tuning' of heptane-plus properties during fluid modelling. It is also concluded that a more accurate correlation for estimating the molecular weight of light crudes has been developedItem A simple generalized equation of state(Society of Petroleum Engineers, 2005) Isehunwa, O. S.; Falade, G. K.A pressure perturbation technique based on a simple adaptation of the Weirtheim's first order thermodynamic perturbation theory has been developed and used to formulate a generalized equation of state. The practical equation formulated was applied to pure fluids, binary systems and real samples of Niger Delta Petroleum fluids. Tuning of data is not required. The results show more accurate predictions than the commonly used SRK and PR equations. This work provides a theoretical framework for improving the accuracy of cubic equations of state. One major advantage of the generalized equation expressed in this work is the fact that it provides a theoretical framework for explaining the physical significance of the parameters in multi-parameter equations of state. Thus, in a three-parameter equation of state, while 'a' captures the attractive forces, 'b’ is the co-volume, 'c ' could represent non-physical forces. This is different from the concept of 'c' in such equations as Peng-Robinson EOS where 'c ' obviously represents an "after-the-fact" volume correction term.Item A correlation to predict the viscosity of light crude oils(Society of Petroleum Engineers, 2006) Isehunwa, O. S.; Olamigoke, O.; Makinde, A. A.Direct viscosity measurements are often expensive or unavailable. Therefore, empirical correlations are often used for predicting the viscosity of crude oils. However, several published correlations are either too simplistic or too complex for routine operational use. Many of the common correlations in use were developed using data from other regions of the world, Empirical correlations for predicting the viscosity of light crude oils in the Niger Delta have been presented in this paper. Data from over 400 oil reservoirs from the Niger Delta were collected. The samples were representative of the two crude oil viscosity regimes: above and below the bubble point. After normal quality checks, non-linear multiple regression with linear partial correlation coefficient techniques were used to establish simple correlations between viscosity, pressure, temperature, oil specific gravity and solution gas oil ratio. Statistical error analysis of the developed correlation showed average absolute relative percentage error of 4.00% and 3.25% and R2 of 0.99 and 0.97 for oil viscosity above and below the bubble point respectively. These results constitute considerable improvements over existing correlations.Item Sand failure mechanism and sanding parameters in Niger Delta oil reservoirs(2010) Isehunwa, O. S.; Farotade, A.Sand production is a major issue during oil and gas production from unconsolidated reservoirs. In predicting the onset of sand production, it is important to accurately determine the failure mechanism and the contributing parameters. The aim of this study was to determine sand failure mechanism in the Niger-Delta, identify the major contributing parameters and evaluate their effects on sanding. Completion and production data from 78 strings completed on 22 reservoirs in a Niger Delta oil Field were evaluated. Sand failure mechanisms and contributing parameters were identified and compared with published profiles. The results showed that cohesive stress is the predominant sand failure mechanism. Water cut, Bean size and gas oil ratio (GOR) impact sand production in the Niger Delta.Item Rheological properties of treated oil well cement contaminated by pseudo oil based mud(2010) Isehunwa, O. S.; Uzoalor, E. I.Contamination of cement slurries during oilwell cementing distorts their designed properties and leads ultimately to poor cement jobs. To promote best practices and enhance cementing successes, it is always desirable to understand slurry response under different conditions such as contamination. Appropriate corrective measures can then be undertaken when necessary. This study carried out complete rheological experimental characterization of oil well cement slurries contaminated by pseudo oil based muds (POBM) and treated with additives. Results show that gel strength increases with POBM contamination for all types of cement slurries.Item Evaluation of true government take under fixed and sliding royalty scales in Nigerian oil industry(2011) Isehunwa, O. S.; Uzoalor, E. I.Fiscal regimes are very important in the global Petroleum Exploration and Production (E&P) industry. They sharpen policies, management strategies and revenue (take) by governments while defining the attractiveness of the industry to investors. One of the major parameters in fiscal regimes is royalty oil, which could be fixed or adjustable on a sliding scale. Nigeria, which has used fixed royalty scale since the first oil in 1958, is now proposing a change to the sliding royalty scale method within a general review of the country's fiscal regime terms. This study investigated the impact on Government take of a change to sliding royalty in both Joint Ventures (JV) and Production Sharing Contract (PSC) arrangements. Generalised cash flow models to evaluate true government take were developed under conditions of royalty scales based on either or both oil price and volume of production. The results show that government take under sliding royalty scale rates compared favourably with take under fixed royalty rates. However, sliding royalty rates calculated based on both oil price and volume of production yield higher government take than those based on either volume of production or price of oil alone.Item Effects of fiscal terms and contractual agreements on government take in Nigerian oil industry(2009) Isehunwa, O. S.The effects of fiscal terms on true government take under joint petroleum ventures and production sharing contracts were investigated. A generalized cash flow model was developed and used to evaluate government revenues under different fiscal terms and contractual agreements. Analyses revealed that government take is reduced in joint ventures with divestment of equity if other fiscal terms remain unchanged.Item Effect of operating conditions on acoustic gas metering in the Niger Delta(2011) Isehunwa, O. S.; Harry, Y.This study investigated the relationship between velocity of sound and properties of natural gases under different equations of state and the operational implications on acoustic gas metering. The velocity of sound was related to the thermodynamic properties of natural gas using both the Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) equations of state and applied to 5 wet and 5 dry natural gas samples from the Niger Delta at different conditions of temperature and pressure. Predicted results were statistically analyzed and compared with experimental data. For wet gas, SRK and PR equations gave average absolute deviation (AAD) of 9.50% and 1.15% for velocity of sound respectively: while AAD of 0.943% and 7.021% were obtained for dry gas using the SRK and PR equations respectively. Predictions of sonic velocity and gas properties using both SRK and PR tend to give higher accuracy at high pressures than at ambient pressures and temperatures suggesting that correction factors must be implemented tor ambient metering of gases when acouistic meters are used.