EnSys Yocum offers a powerful suite of field proven, accurate multiphase software for oil and gas production systems design, performance improvement and flow measurement.  

The Virtual Metering Simulation Software Package(VMSS3) simultaneously calculates the multiphase/single phase engineering fluid dynamics, heat transfer, and thermodynamic relationships for oil and gas/condensate wells and their downstream production facilities gathering systems. Thus, the VMSS3 provides the Client with accurate flow rate measurements for the three phase flows of gas, oil/condensate, water, and provides the pressure/ temperature/ flow rate information for simulation and optimum operation and design of the production systems. The VMSS3 package can now tie in with the Field Data Acquisition System (DAS) for instant online real time calculations. A detailed description of VSSM3 is contained in the downloadable technical description.

The VMSS3 technology has been under development during the last thirty years and has undergone rigorous field production testing in 413 wells and production facilities that produce from reservoirs with varying reservoir fluid properties. Applications have been made in 60 oil and gas/condensate field projects to provide optimal designs. Applications can be made in well/producing systems with limited experience or scarce data by simulating against the extensive virtual memory data banks that have been built up in 60 fields and several hundred applications.

The VMSS3 package should be applied to wells and their production systems to improve the accuracy of multiphase flow rate measurements and to reduce field investments and operating costs. Please refer to the categories below:

• to provide accurate well multiphase flow rate measurements without the need to install expensive wellhead or downhole multiphase meters or wellhead separators.

• to provide improved production testing for multiphase meters located at a distance downstream from wells-at the end of flowlines, production manifolds, or trunkline junctions. The VMSS3 package operates in parallel with the multiphase meters, thus enabling accurate multiphase measurements to continue when the multiphase meter is out of service (10 –30% of the time), and provides meter proving and calibration capability for the multiphase meters.

• provides pressure/temperature/flow rates for future field conditions, as example, declining reservoir pressures, increasing water cuts, and increasing gas/oil ratios.

• calculates the flow rate increases generated from adding facilities modifications to the well and production systems. VMSS3 can be used to evaluate the most economical cost/benefit production system additions.

Multiphase Choke Flow and Pressure Drop Prediction

An Excel Spreadsheet Program calculates the Critical and Subcritical Flow of Multiphase mixtures through chokes. The complex and rigorous calculation procedure utilized is described in SPE Paper 20633 published by T.K. Perkins, Arco E&P Technology. The method has been further refined by allowing the user to introduce physical property changes reflecting the liberation of gas between the upstream flow conditions and the choke throat, and by extending the range of flow conditions for which the program may be used. These extend to bottom hole well chokes for HPHT reservoirs:

• P up to 10,000 psig and T to 300 degrees F, with allowance for the user to input compressibility factor (z) and Cp/Cv (k) ratio at P and T higher values.
• 3-phase flow systems
• Applicable to MOV and Multistage Choke Calculations
• Applicable to critical and subcritical flow
• Calculation of mass flow rate and volumetric phase flow rates
• or back-calculation of the discharge coefficient (Cd)

Perkins reported testing the method against 1,432 data points with a standard deviation of 15.4 % and no bias detected. The data comprised both critical and subcritical regimes for gas/oil, natural gas/water and other systems. With basic physical property data inputs, our checks against field data for crude oil flow indicate that the spreadsheet program will predict multiphase flow rates within an accuracy of 10%. With the user calibration of the choke discharge coefficient against field tests this accuracy should improve.

A spreadsheet "wizard" is installed to guide the user through the inputs and the output options. Accurate estimates of oil and gas phase densities and GOR are required inputs for standard, upstream and choke throat conditions in order to achieve the most accurate flow rate prediction. A brief user manual is also supplied.

• As a metering device with an accuracy of 10% or better

The well choke is a necessary control device in the production system to lower surface pressure and has been viewed as a possible source of inexpensive well flow rate measurement. However past field experience with simplified choke correlations for multiphase flow showed accuracy of only +- 25 %, which was inadequate for well testing. The use of our advanced program can improve well reservoir management.

• As a check against test separator results

Test separators are usually installed in production systems to carry out the multiphase well testing function. Engineered production tests in test separators have been routinely able at best to measure multiphase flow rates to +- 10 %, however installing the test separator units including their process equipment and instrumentation units is expensive especially on offshore platforms. Confidence gained by applying the choke program could significantly reduce field operation costs.

• As a check against multiphase meter flow measurements

Multiphase meters have been known to experience downtime and accuracy problems when applied over a range of flow conditions. The choke program provides an ongoing redundancy check and a means for their calibration.

• As an aid to Virtual Metering

During the last 30 years there has been significant development and improved understanding of the fundamental equations, correlations and computational processes that describe the fluid flow, thermodynamic, and heat transfer processes in the fluid flowing from the reservoir through the well and then through the production system to the separators. This advanced engineering technology and software is contained in our Virtual Metering Simulation Software package (VMSS3) that can be applied either online or offline for well/producing system multiphase flow rate measurements. The accuracy of well test measurements are improved to the +- 5 – 10 % in producing systems and +- 1 –2 % in wells. The VMSS3 software package can work in parallel with lower cost multiphase flow choke devices given their accurate flow rate prediction.

• Chokes have been observed to exacerbate emulsion formation. The accurate prediction of choke pressure drop versus flow rate provides a means of predicting the maximum droplet size and droplet size distribution. This is of particular interest in analyzing offshore water disposal problems and the application of hydrocyclones and aeration vessels.

• Chokes have been applied to slug-flow control by reducing the pipe cross sectional area and modifying the passing slugs. The accurate prediction of choke pressure drop versus flow rate provides a means of predicting the choke effects on slug length and holdup. An important function of chokes is to break up large incoming slugs from wells and production lines, especially in hilly terrain, before they enter the first stage separator, so that the separator can operate more economically at increased flow capacities.

 

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GOSPSIM-3 Gravity & Cyclonic Separator Simulation

The EnSys Yocum GOSPSIM model employed is a rigorous, multi-phase, steady-state, pressure temperature flow (PTQ) simulator designed for and proven against hundreds of oil and gas field production systems. The version of GOSPSIM applied here encompasses from the well-head through the surface facilities, including separators, to the terminus. Other versions encompass integrated simulation from the reservoir pay and well bore through the surface facilities, multi-well trunk line network systems and, prospectively, horizontal/multi-lateral well systems. The scope encompasses crude with associated gas, gas condensate and gas systems as well as black oil simulation.  

A detailed technical description incorporating field applications examples and commentary on EnSys Yocum separation experience with chemicals applications is contained in the  downloadable technical description.

Integrated modeling of separators within the context of the entire flow system establishes the approach conditions, including predicted slug size and frequency and the incoming flow regime. The approach flow regime may be stratified and this pre-separation provides additional separating capacity provided that a correct stilling box or flow diverter is installed. However, if the flow regime is homogeneous, separation is aided by passing the incoming flow through a jet forming nozzle which impinges on a target plate to form maximum separation between the gas and liquid phases.

Both (one) gravity and cyclonic centrifugal force technologies are contained in the GOSPSIM 3.3 3-phase Separator Simulation. Model.

The following are key features of GOSPSIM with respect to gravity separation:

The model can be run in two basic modes:

(a) the design mode which sizes the separator for the specified oil, water and gas rates given the separator pressure, temperature and fluid properties. In this mode, the separator is sized to 1.0 percent water cut in the oil, 0.1 to 0.5 gal per of liquid carry over per mm scf of outlet gas, and gas carry under of 0.02 GVF or less. Design droplet sizes may be input or provided by the model.

(b) the simulation or operating mode under which the separator size and design basis droplet sizes are specified (or calculated) and the effluent gas, water and oil qualities are calculated in response to varied flow rates, water cut, physical properties, internals, liquid levels and separator conditions.

Several approaches are compared within the model to arrive at a separator design size:

(a) the use of model-contained EnSys Yocum engineered field test data bases to establish liquid and gas residence times. Our simulation efforts commenced in the 1970’s and early 80’s based on approximately 200 production tests that had been carried out on gas/ oil separators in thirteen fields with different reservoir fluid properties. An extensive data base of fluid properties has been constructed, permitting the model to achieve high accuracy with simplified methods and within real world data limitations.

(b) sizing for gas capacity based on entrained liquid droplet settling theory. The maximum gas velocity to avoid liquid re-entrainment is calculated;

(c) gravity separation of the rising oil droplets based on Stoke’s law, but also taking into account non-ideality and short-circuiting due to turbulence. The maximum horizontal liquid velocity is calculated and compared to the terminal velocity of the rising oil droplet to calculate a design factor expressing non-ideality;

(d) water droplet settling theory based on Stoke’s law;

(e) overflow velocity analysis;

(f) calculation of maximum oil pad thickness;

(g) input retention oil, gas and water retention times based on API 12J common practice, Petroleum Engineering Handbook criteria or bottle/ standpipe tests.

The minimum water droplet design size corresponding to a 1% water cut in the effluent oil is taken as an input or calculated. For conventional FWKOs with a water-wash coalescing section, this diameter correlates closely with oil viscosity and can be increased by installing an electrostatic treater.

An water droplet design size is back-calculated corresponding to higher (or lower) flow rates, viscosity, other fluid property changes and different separator conditions. This back calculated droplet size is then compared to the above 1% water cut value to calculate water-in-oil and oil-in water contents based on relationships contained in the model;

The distribution of oil droplet sizes affects water cleanup strategies to meet water discharge quality requirements.

Other model features include:

(a) internals options including inlet diverter plate\downcomer designs of different primary stage separation efficiency, gas outlet wire mesh pads, perforated plates in the liquid zone, wave plates, vanes, wave plates and structured packing. Also a vortex breaker design over the liquid outlet to prevent gas coning at low liquid operating levels).

(b) effect of slug and surge flow on separator size

(c) vessel weight and cost calculation

(d) accounting for the separator volumes occupied by foam and emulsion layers

(e) slenderness ratio optimization

(f) inclusion of electrostatic treaters and separator heaters.

The incorporation of cyclonic centrifugal force technologies with the conventional (one g) 3-phase separation process are described below.

Because of the increasing water cuts, and higher GORs as fields age, increasing difficulty in the separation of the phases due to high viscosities, foaming crude mixtures, slug flows entering the separators, sand collection and disposal, and other problems, it has become economical in many fields to add Cyclonic Separation Technologies.

Effective cyclonic equipment of several designs has been deployed in the field. Production data has become available on some designs. Therefore, GOSPSIM 3.3 now incorporates some of the more widely applied cyclonic unit performance characteristics and design limits.

 

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Horizontal / Multi-lateral Well Simulation (WELLSIM)

The EnSys Yocum WELLSIM Model has the following capabilities:

 

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Production Facilities Simulation (PRODSIM)

The Production Facilities Pressure Temperature/Flow Rate (PTQ) Simulation Computer Model (PRODSIM) describes the flow performance for the production system beginning at the reservoir, flowing through the well reservoir pay, then up the well, and through the surface or underwater facilities, devices and pipelines to the production manifold.

A companion computer simulation model, GOSPSIM, receives as input the multiphase flow rate, pressure, and temperature at the production manifold. GOSPSIM simulates the separator and process flow performance of the Gas/Oil/Water Separation plant and the associated downstream processing facilities.

A detailed description of PRODSIM is contained in the downloadable technical description.

Multi-well Trunkline Simulator (TRUNKSIM)

The EnSys Yocum Multi-well Trunk Line Network Model is a powerful model for optimizing the development of fields when trunkline networks operating in single or multiphase flow are being considered for up to 100 oil wells producing simultaneously.

A case study feature permits the automatic generation of alternative network figurations for determining the optimum field producing systems and for examining the technical feasibility of each alternative.

This model is particularly well adapted to the design of offshore subsea gathering systems

Additional detail is contained in the downloadable technical description.

PVT Meter Program (PVT-MPM)

The EnSys Yocum PVT Meter Correction Programs are capable of correcting multiphase meter liquid and gas flow using PVT data that describes the metered fluid. The programs have many useful features which are described in downloadable technical description.  Among these are: