Claudio Alimonti

Multiphase Flow Metering: Current Trends and Future Developments

Over the last decade, the development, evaluation, and use of multiphase-flow-metering (MFM) systems have been a major focus for the oil and gas industry worldwide. Many alternative metering systems have been developed, but none can be referred to as generally applicable or universally accurate. Both established and novel technologies suitable to measure the flow rates of gas, oil, and water in three-phase flow are reviewed and assessed within this framework. Technologies already implemented in various commercial meters then are evaluated in terms of operational and economical advantages or shortcomings from an operators point of view. The lessons learned about the practical reliability, accuracy, and use of available technology are discussed. As operators now realize, use of MFM systems (MFMSs) is essential in exploiting marginal fields. A new approach to flow assurance, deepwater developments, downhole/seabed separation systems, and wet-gas fields is foreseen. The authors suggest where additional research to develop the next generation MFM devices will be focused to meet the as yet unsolved problems.

Evaluating the Available Regional Groundwater Resources Using the Distributed Hydrogeological Budget

In this study, several hydrogeological catchments of Central Italy have been characterized focusing the attention on the presence of areas in which, over the last two decades, the hydrological equilibrium between recharge and discharge (phenomena of marked reduction of spring discharge and progressive drawdown of groundwater levels) has been compromised by overexploitation of groundwater resources. A GIS system has been used in order to develop the study and the homogenous distribution of the hydrological knowledge and of the existing imbalances has been performed. Characterizing elements of the research are: a) the definition of the hydrogeological units; b) the hydrogeological survey of around a thousand water-points; c) the monthly analysis of climatic data of numerous survey stations; d) the census and the recording of water concessions; e) the evaluation of agriculture hydro-exigency derived from the analysis of the use of soil; f) the withdrawals defined by a statistic analysis of data. These elements have allowed to define the Distributed Hydrogeological Budget which is a useful instrument to evaluate critical areas.

Reliability Analysis for Preliminary Forecasts of Hydrogeological Unit Productivity

The aim of this work is to find a probabilistic characterization of the productive capacity of a well in a geological formation hosting an aquifer. Such characterization in terms of productive capacity may allow a preliminary assessment to be made of the probability of success for a required productivity (i.e. target point). This evaluation is usually carried out by statistical analysis of a geological dataset, which is likely to be influenced by many parameters. Such datasets are often incomplete or unreliable. Therefore, a method for evaluating potential productivity, using probabilistic hydraulic conductivity data, is proposed. The hydraulic characterization of hydrogeologic units is based on the collection of information obtained mainly through pumping tests and their interpretation. The results, expressed in terms of hydraulic conductivity, are summarized in a range of variability that is strictly dependent on the number of performed tests and their spatial distribution in the unit itself. If this range is known, an estimate of well’s yield can be made on a deterministic basis, through Thiem’s relationship for steady state conditions, by setting a value of hydraulic conductivity that corresponds to the average value of the range. The proposed reliability analysis enables to overcome the limitations of the deterministic approach by correlating each calculated flow rate, which is taken to be a design flow rate exceeding the critical flow rate of the hydrogeologic unit, to its probability of failure. Therefore, this approach aims to evaluate the probability of failure of the water system. The preliminary result is to associate the values of aquifer exploitation with a probability failure function. This outcome can then be used to define the potential solutions in the optimal allocation of the withdrawal by means of reliability analysis that takes into account the uncertainty of the system.

The Challenges of Multiphase Flow Metering: Today and Beyond

Since the early 1990’s, when the first commercial meters started to appear, Multiphase Flow Metering (MFM) has grown from being an area of R&D to representing a discipline in its own right within the oil and gas industry. The total figure for MFM installations worldwide is now over 1,800. Field applications include production optimisation, wet gas metering, mobile well testing and production allocation. However, MFM has not yet achieved its full potential. Despite an impressive improvement in the reliability of sensors and mechanical parts (particularly for subsea installations) over the past few years, there remain unresolved questions regarding the accuracy and range of applicability of today’s MFM technology. There is also a tendency to forget the complexity of multiphase flow and to evaluate the overall performance of a MFM as a “black box”, often neglecting all the possible uncertainties that are inherent in each individual measurement solutions. This paper reviews the inherent limitations of some classical MFM techniques. It highlights the impact of instruments rangeability, empirical correlations for pressure drop devices and fluids characterisation on the error propagation analysis in the “black box”. It also provides a comprehensive review of wet gas definitions for the oil and gas industry. Several attempts have been made to define “wet gas” for the purpose of metering streams at high gas-volume-fractions, but a single definition of wet gas still does not exist. The measurement of multiphase flows presents unique challenges that have not yet been fully resolved. However, the challenges are exciting and the authors have no doubts that new milestones will soon be set in this area. Today’s MFM technology has already become one piece of the optimised production system jigsaw. MFM has succeeded in fitting with other technologies toward global field-wide solutions. The ideal MFM of the future is one that provides unambiguous measurements of key parameters from which the flow rates can be deduced independently from flow regimes and fluid properties.Copyright

Potential for Harnessing the Heat from a Mature High-Pressure-High-Temperature Oil Field in Italy

Significant volumes of water are co-produced with oil and gas in mature hydrocarbon developments. Often, the produced fluids are at high temperatures, and cooling is therefore required. However, because of the large volumes involved, one might consider exploiting the co-produced waters geothermal potential in order to reduce both the fields OPEX and the fossil energy needed to continue extracting the hydrocarbons, and so extend the life of the field by delaying its economic cut-off point. Also, there is scope for eliminating the field abandonment costs for the oil and gas operator, who could hand over the field to a geothermal operator when hydrocarbon production became uneconomic; the geothermal operator would in turn save the initial cost of having to drill and complete wells and install surface facilities. This paper consists of a preliminary assessment of the potential for geothermal exploitation of the co-produced water from wells in the Villafortuna-Trecate oil field in Italy, which has an aquifer that not only provides pressure support to the reservoir, but also represents an in-situ hydrothermal resource, without the need for external water recirculation. The study compares three different implementation scenarios for the possible use of the co-produced hot water: direct use in district heating, electric power generation through an Organic Rankine Cycle (ORC) plant, and co-generation of heat and power. The results suggest that, for the power generation option, a single well draining a cylindrical reservoir drainage area could recover approximately 25 GWh of electric power over a 10 year period with an installed capacity of 500 kW. With the co-generation option, which appeared to be the most appealing, a lower net electrical power of 143 kW per well could be obtained, but at the same time approximately 46 utilities could be served by a 660 kW district heating plant per well. There remain potential permit and licensing issues associated to the concept of harnessing thermal energy from oil and gas developments, depending on the specific country and legal process. For example, it is often the case that the terms and conditions associated with a geothermal exploitation lease are quite different from a hydrocarbon lease.

Using Transient Inflow Performance Relationships to Model the Dynamic Interaction Between Reservoir and Wellbore During Pressure Testing

The fundamental understanding of the dynamic interactions between multiphase flow in the reservoir and that in the wellbore remains surprisingly weak. The classical way of dealing with these interactions is via inflow performance relationships (IPR’s), where the inflow from the reservoir is related to the pressure at the bottom of the well, which is a function of the multiphase flow behaviour in the well. Steady-state IPR’s are normally adopted, but their use may be erroneous when transient multiphase flow conditions occur. Transient multiphase flow in the wellbore causes problems in well test interpretation when the well is shut-in at surface and the bottomhole pressure is measured. Pressure build-up (PBU) data recorded during a test can be dominated by transient wellbore effects (e.g. phase change, flow reversal and re-entry of the denser phase into the producing zone), making it difficult to distinguish between true reservoir features and transient wellbore artefacts. This paper introduces a method to derive the transient IPR’s at bottomhole conditions in order to link the wellbore to the reservoir during PBU. A commercial numerical simulator was used to build a simplified reservoir model (single well, radial co-ordinates, homogeneous rock properties) using published data from a gas condensate field in the North Sea. In order to exclude wellbore effects from the investigation of the transient inflow from the reservoir, the simulation of the wellbore was omitted from the model. Rather than the traditional flow rate at surface conditions, bottomhole pressure was imposed to constrain the simulation. This procedure allowed the flow rate at the sand face to be different from zero during the early times of the PBU, even if the surface flow rate is equal to zero. As a result, a transient IPR at bottomhole conditions was obtained for the given field case and for a specific set of time intervals, time steps and bottomhole pressure. In order to validate the above simulation approach, a preliminary evaluation of the required experimental set-up was carried out. The set-up would allow the investigation of the dynamic interaction between the reservoir, the near-wellbore region and the well, represented by a pressured vessel, a cylindrical porous medium and a vertical pipe, respectively.Copyright

The MtBE Removal Effectiveness of Air Sparging, Tested on an Intermediate Scale Laboratory Apparatus

Among all the in situ groundwater remediation treatments designed to remove MtBE and other gasoline components, Air Sparging (AS) has been widely used since it is one of the best established, econom ical and reliable technologies for the remediation of volatile compounds dissolved in groundwater. However although AS has been successfully applied at several contaminated sites, the airflow distribution in saturated media and the interactions of various physical, chemical and microbial processes during AS operations are still not well understood. This experimental study was designed to investigate the effectiveness of AS in removing dissolved MtBE from a saturated media, performing a removal test under confined and controlled conditions in an intermediate scale tank (m 1 × 1 × 1,2). The experimental conditions focused on the study of the stripping process driven by air injection. Stripping is considered to be the most effective removal process driven by AS in the initial period of its in situ application. The study confirmed that in situ AS has significant potential for remediating groundwater contaminated by MtBE, by showing that the stripping action, driven by air injection contributes significantly to the overall removal action of the AS technology.