A high pressure oil or gas well can be used to enhance both the production and the total recovery from a depleted well using a multiphase ejector. This device does not require any power supply and is characterized by a simple design, absence of moving parts and small dimensions, coupled with a high degree of reliability and low cost. The main disadvantages related with the use of multiphase ejectors are due to the lack of reliable design methods and to the sharp decrease of the performance when operative conditions change. In August 2002 a multiphase ejector has been installed in Allegheny TLP, GOM, to boost the production from a depleted well. In the present paper the design method and the results of field tests of the Allegheny ejector are presented. From a practical view-point the main result of this installation has been an increase of production of 1300 BOPD with an investiment of less than 50,000 USD. Introduction The ejector or Jet Pump, JP, is an artificial lift method which does not require any power supply and is characterized by a simple structural design, absence of moving parts and small dimensions, which allows easy installation and management procedures during fields operations, coupled with a high degree of reliability and low cost of installation, compared with other boosting systems. On the other hand, the ejector is a low-efficiency device: just a small fraction of the power fluid energy (approximately 20-30%) is actually transferred to the low pressure fluid (however it should be remarked that in many cases this energy would be lost through a choke valve). When the ejector is fed with multiphase fluids, significant modelling problems arise and no established methods are available for the design of multiphase ejectors. Design problems are increased by fluid properties changes during field evolution. To cope with all these problems and extend the operative life of the ejector, an advanced multiphase ejector has been developed in order to optimise some of the main geometrical parameters and improve the ejector performances at varying operative conditions. In this paper, the realization and field application of this multiphase ejector are described. Fig. 1 shows the main components of a JP: the nozzle, the mixing chamber followed by the mixing duct and the diffuser sections. Power fluid, at an injection pressure Pd is forced through the nozzle. As the fluid accelerates because of the area reduction, its kinetic energy increases and the pressure decreases to the value Pn at the nozzle exit section. The power and the produced fluids then enter the mixing chamber were pressure reaches its minimum value, Ps. In the mixing chamber, mixing duct and diffuser the pressure increases and the gas-liquid mixture leaves the ejector at a pressure Pl. The main concern about actual multiphase ejectors is the limited capability of the hardware to be adjusted when boundary conditions change (i.e. well depletion, water cut and/or GOR variation, production profiles). To this aim, the present multiphase ejector has been designed to be adaptable in terms of:
This paper presents a case study from the ENI operated Muara Bakau PSC (Jangkrik) on the East Kalimantan shelf edge and the west slope of the Makassar straits. The paper discusses the resolution and accuracy of Short-Offset Processed 3D Seismic Data (SOPS) and the applicability of the resulting Digital Terrain Models (DTM) for seabed mapping and initial field development planning. For this case study a SOPS DTM of 12.5x12.5m grid spacing was generated covering a total area of 330 Km². A somewhat smaller area was later surveyed utilising an Autonomous Underwater Vehicle (AUV). The resulting AUV DTM was of 1x1m grid spacing. A number of exploration wells were already drilled within the area and accurate water depth measurements were performed from three of those wells. This provided the opportunity to evaluate the SOPS DTM accuracy and resolution. The results of the evaluation are presented in this paper. In the Jangkrik Project development, the SOPS DTM execution at early stage (during Concept Selection) allowed to: Progress the subsea system design of a "fast track" project without waiting for site geophysical survey (AUV) Make key decisions at early stage avoiding the cost and time impact of later changes such as: One well (JK 7) was relocated because initially positioned within a canyon
Summary The first field installation of a multiphase surface ejector was successfully accomplished in the Villafortuna oilfield (Italy) in 1996. The ejector increased the oil production rate by 30% and demonstrated the viability of the system as a reliable low cost-small size boosting system that had minimal impact on existing facilities, and is suitable for applications in existing fields or for new development both onshore and offshore. The article describes the main steps of the R&D project, developed in collaboration with the University of Ancona, as well as the testing process in which different ejector geometries were extensively tested with crude oil and gas in the Agip's multiphase loop of Trecate. The article describes the installation in the Villafortuna field as well as other studies under development. Introduction The ejector is a static machine in which a high pressure stream (HPS) is mixed with a low pressure stream (LPS) in a properly designed mixing chamber. The mixture passes through a diffuser, leaving the ejector at an intermediate common outlet pressure (Fig. 1). The ejector is a well known piece of equipment that is used extensively in many industries in all the chemical industry (gas-gas ejectors) and nuclear industry (liquid-liquid jet pumps). The oil industry limited the use of jet pumps at the bottom hole as an artificial lift system, using water or diesel as the power fluid pumped from the surface. For the bottom hole jet pumps the approach used is to treat the gas phase in the low pressure stream (suction stream) as a "liquid phase." This is usually correct for down hole jet pumps, where the gas carried under the liquid stream is frequently limited to small percent (5 to 10%). This assumption is not valid for surface oil ejectors because the gas greatly exceeds this limit. As far as we know, at present, no one is using surface ejectors for oil wells. Instead, for gas wells field applications have been successfully realized in recent years by Agip and others. In this article the results of Agip applications are reported. The installation of an ejector on the surface allows one to use free energy from a high pressure well (if present, of course) to boost a low pressure well, thereby obtaining enhancement of the well production and/or extension of the field life. In 1993 Agip launched a R&D project in collaboration with the University of Ancona aimed at analyzing the suitability of ejectors as boosting systems for marginal oil wells. Starting with a preliminary analysis of the existing literature, the project progressed with the development of a software design based on a simplified theoretical model. The experimental coefficients of the model have been tuned while testing the ejectors with different geometries in the laboratory of the University of Ancona using water and air at low pressures in a wide range of process conditions. A second tuning followed the test performed in the Trecate Test Loop (TTL) with live hydrocarbons at high pressure and the model is now more user friendly software, able to design a multiphase ejector working with medium and light crude oil, within an error that is smaller than 10%. The R&D Project The project was developed in two main steps:laboratory tests and code definition;field test and code updated. Laboratory Tests and Code Definition The studies on multiphase ejectors started from activities previously performed on bottom hole jet pumps using water or diesel as the power fluid pumped from the surface. From the literature1,2 it was clear that the conservative approach used in the past was to treat the gas phase in the suction as "liquid phase." This is correct whenever the gas carried under the liquid stream is limited to small percentage, 5 to 10%. When the gas exceeds these limits, which always occurs for surface ejectors, the equations used for the liquid only have to be modified. Three theoretical-experimental software design was developed for liquid-gas (LG) ejectors (liquid in the drive stream and gas in the suction stream), liquid-multiphase (LM) ejectors and multiphase-multiphase (MM) ejectors, taking into account the gas void fraction (GVF) in one or both of the drive and suction streams. All of them where based on the equation of energy and momentum conservation in order to evaluate the pressure difference between the upstream and downstream sections. The models were based on the following common assumption:a monodimensional approach along the flow direction, anda homogeneous mixture of oil and gas in one or both of the steams. Three main sections were identified: the nozzle, the mixing tube and the diffuser. As was for the models available in the literature, the equations define the structure of the code. However the relations need experimental evaluation of the loss coefficients for the nozzle, the mixing tube and the diffuser. The test facilities at the University of Ancona (Fig. 2) were updated to allow testing of the LG, LM and MM ejectors. Over 400 tests3 at low pressure have been performed working on six plastic models with different geometrical arrangements using air and water in a wide range of test conditions shown in Table 1.
The first world-wide (to our knowledge) field installation of a multiphase d c e ejector has been successfully applied in the Villafortuna oilfield (Italy) on 1996. Ejector installed at Villafortuna 4 (VF4) well increased its oil production rate by 30% and demonstrated the viability of the system as a reliable low cost-low size boosting system, with minimum impact on any existing facility, suitable for applications in existing fields or for new development both on-shore and off-shore. The paper describes the main steps of the R&D project, developed in collaboration with the University of Ancona, aimed at evaluating the suitability of ejectors as simple and low cost-low size boosting system for oil wells. In addition, the reliability of a computer code, developed by Agip and University of Ancona for the design of the ejector, is discussed. The paper also presents the activity of tuning for the software, based on a test campaign in which different geometries of ejectors were extensively tested, before with air and water at low pressures, in the laboratory of University (over 400 data points), and after with crude oil and gas in the Agip's multiphase loop of Trecate (over 200 data points).the tests have been executed varying pressure, liquid flowrate, gas-void fraction and outlet common pressure, both for the high pressure stream and for the low pressure stream, covering a wide range of process conditions. Following the good results obtained from the tests, the installation of a multiphase ejector at Villafortuna 4 well has been realized; The paper describes such installation as well as other studies under development. INTRODUCTION The ejector is a static machine in which a High Pressure Stream (HPS) is mixed with a Low Pressure Stream (LPS) in a properly designed mixing chamber. The mixture passes through a diffuser, leaving the ejector at an intermediate common outlet pressure (Fig. 1). The ejector is a well known equipment extensively used in many industries such as chemical industry (gas-gas ejectors) and nuclear (liquid-liquid jet pumps). The oil industry limited the use of jet pumps at the bottom hole as artificial lift system, using water or diesel as a power fluid pumped from the surface. For the bottom hole jet pumps the approach used is to treat the gas phase in the low pressure stream (suction stream) as a "liquid phase". This is usually correct for down hole jet pumps, where the gas carried under the liquid stream is frequently limited to small percent (5-10). This assumption is not valid for surface oil ejectors because the gas largely exceed this limit.
The application of a new Multi Phase Flow Meter (MPFM) for monitoring the production of three gas wells in the Gulf of Mexico, Allegheny TLP, is presented. The meter is based on a sampling method, does not make use of γ-sources and is selfcalibrating. In the present application, it has been possible to compare the measurement of the MPFM with production data obtained from a conventional well testing system certified for production allocation. The accuracy of present measurements of the gas and total liquid flow rates is similar (or better) than the accuracy of the well testing system (± 2% of the actual readings). A special feature of this MPFM is the direct measurement of the condensate and water phase densities. This allows a very accurate measurement of the Water Volume Fraction, with an absolute uncertainty of WVF measurements equal to 0.001%. This value is two orders of magnitude better that the accuracy of other MPFMs under development. The measurement of the water phase density also permits an estimate of the methanol flow rate injected in the subsea pipeline to prevent hydrate formation.
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