Santanu Khataniar

Evaluation of rheological models and application to flow regime determination

Abstract Rheological models are frequently used to predict the shear stress-shear rate behavior of drilling fluids. However, none of these models can accurately predict the rheological behavior of all drilling fluids over all ranges of shear rates. In this study, the following rheological models were used to predict shear stress as a function of shear rate in several mud samples: Bingham Plastic, Power Law (2 point method and least-square method), Herschel-Bulkley and Robertson-Stiff. The first objective of this study was to identify the model that provided the best overall match of the experimentally observed rheological data. This was done by democratic ranking of the rheological models based on error analysis. The Robertson-Stiff model provided the best, and the Bingham Plastic model provided the worst overall prediction of rheological behavior. The second objective of the study was to develop a new method for determination of flow regimes in pipe flow using the Herschel-Bulkley and Robertson-Stiff models. The proposed method has been shown to predict the onset of turbulence in pipe flow more accurately than the conventional method for Bingham Plastic and Power Law models.

Measurement of the Wax Appearance Temperature of Gas-to-Liquids Products, Alaska North Slope Crude, and their Blends

As part of a major project on studying the operational challenges in gas-to-liquids (GTL) transportation through the Trans Alaska Pipeline System (TAPS), the wax appearance temperatures (WAT) of GTL products and the Alaska North Slope Crude (ANSC) and their blends were measured. The WAT measurements of GTL products were based on the American Society for Testing and Materials (ASTM) D3117 standard, whereas the WAT measurements of ANSC and its blends with the GTL products were measured by the viscometry technique. The reliability of the viscometry technique was ascertained by comparing the WATs of the colorless GTL products measured by the ASTM D 3117 method. The WATs measured by the viscometry technique and the ASTM D3117 method were found to be in excellent agreement.

Heat transfer analysis for gas-to-liquids transportation through trans Alaska Pipeline

Abstract Gas-to-liquids (GTL) technology involves the conversion of natural gas to liquid hydrocarbons. In this article, theoretical studies have been presented to determine the feasibility of transporting GTL products through the Trans-Alaska Pipeline System (TAPS). To successfully transport GTL through TAPS, heat loss along the route must be carefully determined. This study presents heat transfer and fluid dynamic calculations to evaluate this feasibility. Because of heat loss, the fluid temperature decreases in the direction of flow and this affects the fluid properties, which in turn influence convection coefficient and pumping power requirements. The temperature and heat loss distribution along the pipeline at different locations have been calculated. Fairly good agreement with measured oil temperatures is observed. The powers required to pump crude oil and GTL individually, against various losses have been calculated. Two GTL transportation modes have been considered; one as a pure stream of GTL and the second as a commingled mixture with crude oil. These results show that the pumping power and heat loss for GTL are less than that of the crude oil for the same volumetric flow rate. Therefore, GTL can be transported through TAPS using existing equipment at pump stations.

Sodium orthosilicate: An effective additive for alkaline steamflood

Steamflood performance often suffers from channelling and gravity segregation, resulting in poor sweep efficiency. Alkaline additives may be used with steam for certain types of crude oils to improve steamflood performance. In this paper, an experimental study is presented to evaluate the effectiveness of sodium hydroxide, sodium metasilicate and sodium orthosilicate for improving steamflood performance in the Wilmington Tar Zone crude oil. The experimental apparatus was designed to completely eliminate heat loss from the core so that the effects of the alkaline additives on saturated steam, rather than on the condensed water, could be studied. The results show that sodium orthosilicate outperforms sodium hydroxide and sodium metasilicate in enhancing oil recovery by a steamflood.

A New Modified Compositional Viscosity Model for Medium-heavy Oils

Viscosity of heavy oils is a key parameter in designing potential enhanced oil recovery methods. The recently proposed semiempirical viscosity model by Lindeloff et al. (2004) was studied in depth. This model is the simplest yet powerful tool for medium-heavy oil viscosities. Based on the analysis, appropriate adjustments have been suggested, with the major one being the division of the pressure-viscosity profile into three different regions. New modifications have improved the overall fit, including the saturated viscosities at low pressures. The %AAD for the data sets studied was found to be 1.37. However, with the limited geographically diverse data, it is not possible to make a comprehensive predictive model. A few limitations of the new model are also stated.

Characterization of Gas-to-Liquid (GTL) and Alaska North Slope Crude (ANSC) Oil Blend Properties for Flow Through the Trans Alaska Pipeline System (TAPS) by Density and Viscosity Measurements

Abstract As part of a major project on studying the transportation of gas-to-liquids (GTL) through the existing Trans Alaska Pipeline System (TAPS), the density and viscosity of GTL and the Alaskan North Slope Crude (ANSC) and their blends were measured. All density and viscosity measurements were performed, using the Anton–Paar vibrating tube densitometer and a cone and plate viscometer respectively, at temperatures ranging from 20 oC to 60 °C at atmospheric pressure. The accuracy of the measured data has been ascertained. In addition to the density and viscosity data, other data reported for GTL and ANSC include compositions. Finally, generalized dens ty and viscosity correlations for the measured data are presented.

Evaluation of the modes of transporting gas-to-liquid (GTL) products through the trans Alaska pipeline system (TAPS)

ABSTRACT As part of a project on studying the transportation of gas-to-liquids (GTL) through the Trans Alaska Pipeline System (TAPS), two GTL transportation modes are evaluated: (i) as single slugs (batches) and (ii) commingled (mixed) with the Alaskan North Slope Crude (ANSC) oil. The pertinent energy equations are solved for both the batch and commingled flow modes. The solutions of these equations are analytically presented for determining among other parameters, the pressure gradient and the slug length required for batching. A comparison of the pressure gradient calculations is presented for the batching and the commingled flow cases.

A Probabilistic Economic Analysis of the Transportation of GTL Blends Through TAPS

Abstract The Alaska North Slope is a potential candidate for gas to liquid (GTL) technology. With over 38 trillion cubic feet (TCF) of natural gas reserves stranded on the Alaska North Slope, GTL technology is considered as a possible method of harnessing the abundant resources. The main objective of this study is to perform a complete economic evaluation using rate of return analysis and the net present value to identify the most favorable commingled mode for the transportation of the GTL products. Crystal Ball software was also used to run sensitivity analysis by using the probabilistic approach to give a clear view of the various scenarios on the project economics. Evaluating the options of transporting GTL products as a blend (commingled) with the Alaska North Slope crude oil through the existing Trans-Alaska Pipeline System is the main focus of this study.

Economic Appraisal of Transporting Gas-to-Liquids Products through the Trans-Alaska Pipeline System (TAPS)

Abstract The Alaska North Slope oilfield is a potential candidate for the gas-to-liquid (GTL) technology. With over 38 Tcf of natural gas occurring on the slope, gas gathering for a GTL facility will be relatively easy. GTL fuels are environmentally friendly (sulfur free) with better ignition and burning properties than conventional petroleum products from crude oil. Evaluating the options of transporting GTL products through the existing Trans-Alaska Pipeline System (TAPS) together with crude oil, either as a blend of crude oil and GTL (commingled) or as alternate slugs of each product (batching), is the main focus of this study. Economic evaluation model was employed using Rate of Return analysis to identify the most favorable mode of transportation of the GTL products. Batching, using modern tracking and sensor techniques, was found to be a more economic mode, yielding the highest rate of return on the investment.

Alaska Gas Hydrate Research and Field Studies

Natural gas hydrates are solid, crystalline, ice-like materials made up of small molecules of gases, mainly methane confined inside cages of water molecules.