network option

Advanced ECLIPSE CourseNetwork Options

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PurposeExtension of P/Q relationships from well head to pipelines

Variable THP limits to group of wells depend on the groups flow rates according to a set of pipe line pressure loss relationships

Facilities to simulate practical facilities/processes:sub-sea completion manifoldAutomatic compressors/pumpsAutomatic chokes


Well Inflow/Outflow PerformanceProduction RateBottom Hole PressureTubingPiOperating point


Node Inflow/outflow PerformanceUpstream PressureFlow rateOutflowInflowOperating point


Network Segment Example


Facilities in Network OptionStandard Network: the network structure is the same as the group control hierarchyPumps/compressorsGas lift

Extended Network: the network structure is independent of the group control hierarchyMulti-level compressorsAutomatic chokes


Group Control in the Network (1)Standard procedure for group controlwells THP limits set to the groups nodal pressuregroup target rate is allocated to wells proportional to their guide ratesif some wells cannot produce their shares, other wells make up the restwells THPs are different and > groups nodal pressure => wells chokes between well head and group node


Group Control in the Network(2)Group control for sub-sea manifolds Wells are under a common THP controlThe THP is such that the groups target can be metEquivalent to applying a group chokeIf the THP the group cannot meet target


How to set up a Standard NetworkAssign VFP tables to wells (item 11 of WCONPROD)Define the multi-level grouping tree

GRUPTREE-- Son FatherGR-A1 PLAT-A /GR-A2 PLAT-A /GR-B1 PLAT-B /GR-B2 PLAT-B //


How to set up a Standard NetworkDefine the production networkGRUPNET-- Group Fixed VFP ALQ Manifold Include ALQ=-- Name Pressure Tab (Pump Power) Group? Lift Gas? Dens?PLAT-* 300 /GR-A1 1* 1 1* YES /GR-A2 1* 2 1* YES /GR-B1 1* 3 1* YES /GR-B2 1* 3 1* YES /Platforms have fixed pressure 300 PSIAFour well groups are sub-sea completion manifoldVFP table no. = 9999: no pressure lossInclude lift gas flows in the groups pipeline?NO - No, only gas from reservoirFLO - yes & used as FLO for VFP lookupALQ - yes & used as ALQ for VFP lookup lift gas = sum (ALQ) * WEFAC


How to set up a Standard NetworkDefine an injection networkGNETINJE-- Group Network Fixed VFP -- Name Phase Pressure Tab PLAT-B WATER 14.7 / GR-B2 WATER 1* 2 /

Platform B has fixed pressure 14.7 psia - the pump inlet pressureGR-B2 contains water injectors which are under THP (outlet pres) controlThe injection network is separate from the production networkGroup PLAT-B & GB-B2 could have two independent node pressuresRemember to assign VFP tables for the injectors(item 9 of WCONINJE)


How to set up a Standard NetworkSet production rate targets and limits for any group (optional)

GCONPROD-- Group CNTL OIL WATER GAS LIQU LIMIT AVAIL GUIDE G.R. -- Name MODE RATE RATE RATE RATE ACTION FLD RATE PHASE FIELD ORAT 50000 / / PLAT* NONE 1* 10000 2* RATE YES 1 LIQ /GR* NONE 5* YES 100 LIQ //FIELD oil rate target: 50000 STB/DAYPlatforms water handling limits: 10000 STB/DAYThe four well groups have equal guide rates because they are manifold groups subordinate to a group under rate control


How to set up a Standard NetworkDefine automatic pump/compressor if required

GNETPUMP-- Group RATE PHASE NEW VFP NEW LIFT NEW GAS -- Name LIMIT TAB NO QUANTITY CONSUMP GR-B1 500 OIL 1* 50 /

A pump between GR-B1 to PLAT-B will be on if the oil rate of GR-B1 falls below 500 Stb/DThe pump is represented by the VFP table that is defined previously in GRUPNET with an ALQ of 50 (pump rating)A zero or negative rate limit will turn off this optionThe gas consumption is also subtracted from the flow rate between GR-B1 to PLAT-B


Balancing the Network


How to Set Up a Standard NetworkDefine Network Balance Parameters (optional) Network balancing interval (item 1)>0.0: at the beginning of each time step that starts after the specified interval has elapsed since the previous balancing; e.g. 5 - balancing every 5 days=0.0: at the beginning of every time step target, increase the inlet pressureIf the groups rate < target, decrease the inlet pressureIf inlet pressure = outlet pressure, take other actions (PRORDER) to increase the group productionThe choke inlet node cannot be:fixed pressure nodesource node well-groups source nodes can be designated as manifold groupsThe only pressure drop across a choke branch is that caused by the action of the choke itself. The VFP table in BRANPROP should be set to 9999The wells subordinate to the choke will respond to the choke pressure change whenever they are under THP control. ->ECLIPSE automatically makes the wells unavailable for group control


Summary Output for Network Option GPR - Group nodal pressureGPRG - Group nodal pressure in the gas injection networkGPRW - Group nodal pressure in the water injection networkGPRB - Pressure drop along the groups outlet branch GPRBG - Pressure drop along the groups inlet branch in the gas injection networkGPRBW - Pressure drop along the groups inlet branch in the water injection networkGALQ - ALQ in the groups outlet branch


PRT Output for Network Option The tree structure of the networkGROUP LEVELSHIERARCHICAL DESCRIPTION OF GROUP CONTROL STRUCTURENETWORK OPTION DATA


Other Keywords/facilities(1) GNETDPchange the fixed pressure incrementally so that the production rate and the pressure are within their range of maximum and minimum specifiedCOMPOFFswitch off automatic compressors in the extended network (NETCOMPA) and in the gas field operations (GASFCOMP)NWATREMremove water (rate, frac) from a node in the extended networkwater removal ONLY affects the pressure losses in the downstream branches. So the node must has outflow branchuseful for water re-injection


Other Keywords/facilities(2) WEFACwell efficiency factoritem 3: is time average flow rate used for the extended network branch pressure loss?Default is yes; no: maximum well flow rate used GEFACgroup efficiency factoritem 3: is time average flow rate contributed to the parent node in the extended network?yes - time average flow rate used for all downstream pressure loss no - all down stream pressure losses reflect the full ratethe pressure loss in the outlet branch still reflects the full rate The standard network is always using the full rate


Other Keywords/facilities(3) NEFACdefines efficiency factor for extended network nodes which governs its contribution to downstream nodes in the networkuseful for nodes that do not correspond to groups when GEFAC is usedIt does not change the groups efficiency factor, When the group name is the same as the nodal name, if GEFAC with item 3 being YES is entered after NEFAC, the nodal efficiency factor will get reset by GEFAC


Other Keywords/facilities(4) WNETDPto apply an additional fixed pressure drop between a well's tubing head and its group's corresponding nodeFor a producer: THP limit = group nodal pressure + DPFor an injector: THP limit = group nodal pressure DPDP=1E10: THP limit is unchanged by group nodal pressureThe wells flow is still added to the network flowGroup nodal pressureWell THPDP


Other Keywords/facilities(5) WAITBALprevents PRORDER & GDRILPOT actions being performed until network is balancedWNETCTRLset well control quantity that is held constant after the network has been balanced and until the next balancing calculationdefault is THPothers: LRAT, GRAT, WRAT


Other Keywords/facilities(6) OPTIONSSwitch 33number of network balancing iterations in which a well can be revived after being closed because it cannot operate against its current THP=0, defaults to max(4, NETITR/2) , NETITR - item 3 of NETBALANSwitch 57if flow target is low, it is possible for the chokes pressure drop iterations to change the pressure at the wellheads sufficiently that all wells die together.By default, wells zero flow THP is estimated by assuming all well variables (including BHP) are fixed.Set =1: only assuming that the water-cut and gas friction of the well are fixed. More accurate estimate, but longer calculation


Important Differences in ECLIPSE 300No sub-sea completion manifold group control. It uses automatic choke to apply rate constraints at any level of the network, both standard and extended network.Standard and extended network cannot be mixed.It can use extended network for injection network. It allows to use automatic choke in the injection network. Source node name can be different from its corresponding group name.The network is always balanced in each of the first NUPCOL Newton iterations of every time step. (This is equivalent to setting a negative balancing interval in ECLIPSE 100.)WAITBAL is activated by default Automatic pump/compressor facility is not availableFuel gas can be removed from a node - NGASREM


ReferencesECLIPSE Technical DescriptionThe Network option

The network option is a special extension to both ECLIPSE black oil and compositional. It is designed to extend the calculation of the hydraulics, that is the relationship amongst the pressure loss, the flow rates, water and gas flow fractions, and Artificial Lift Quantities (ALQ), from the well bore to the pipelines. When wells flow into a sub-sea completion manifold which leads to a main pipeline, the tubing head pressure is limited by the pressure at the manifold which varies according to the flow rate, water/gas flow fractions and ALQs in the downstream pipelines. The varying well tubing head pressure affects the well production rates which in turn affect the pressure loss through the downstream pipelines. The interaction between the pressure loss along the pipelines, the tubing pressures of the wells and the flow variables such as the flow rates from the wells and in the pipelines, is simulated by the network options.The network option can also simulate the following practical facilities/processes:Sub-sea completion manifold which makes all the subordinate wells have the same THPsAutomatic compressors which will switch on if a groups oil or gas production rate falls below a specified limit.Automatic chokes which control a groups production targetDuring production, fluid flows from formation to the well bottom hole, then from the bottom hole to the well head. For fixed tubing pressure, the larger the BHP, the larger the production rate along the well bore the outflow. On the other hand, the larger the BHP, the smaller the production rate from the formation the inflow. Since the production rate from the formation must be the same as that along the well bore, the production rate and the BHP are determined by the intersection of the inflow performance curve and the outflow performance curve. The well inflow performance depends on the well connection factors, the phase mobility and the completion cells pressures which are solved together with all the cells in the whole reservoir. The well outflow performance is simulated by the VFP tables which are generated by the VFPi program using correlations. In the network options, a pipeline is treated as a well bore with the upstream (inlet) pressure being the BHP and the downstream (outlet) pressure being the THP. Both the inflow and outflow performance is simulated using VFP tables which can be generated by VFPi program. VFPi handles horizontal and undulating flow lines as well as vertical and deviated well bores. Considering a node in the network, in terms of the inflow, the higher the nodal pressure, the lower the flow rate. But in terms of the outflow, the higher the nodal pressure, the higher the flow rate. The actual nodal pressure and the flow through the node are given by the intersection of the inflow curve and the outflow curve. In the network options, ECLIPSE balances the whole network to get the flow rate through each node and the pressure at each node.The above shows a simple network. Two wells are producing to their well heads. The flows then continue from the wells heads through two pipelines to a junction. The flows from the two wells are merged at the junction, and continue through a main pipeline to the separator where the pressure is fixed. To simulate the flow through the pipelines using the network options, firstly we translate the pipelines into networks as shown above on the right hand side. The networks consist of three flow lines (branches) and four nodes. One of the node is the fixed pressure node. In order to have continuous flow through the networks, the wells tubing head pressures must be larger or equal to the groups nodal pressures (THP1>=P2, THP2>=P3), and the the upstream pressure must be larger than the downstream pressure (P2>P1>P0, P3>P1>P0). To calculate the pressure losses through the flow lines, a VFP table needs to be prepared for each flow line (branch). During the simulation, ECLIPSE balances the network calculating the pressure loss along the flow line, the nodal pressures, the wells THPs, the flow rates from the wells, and the flow rates through each flow line.There are two types of network facilities in the network options: the standard network and the extended network. When the standard network is used, the network structure must be the same as the group hierarchy defined by GRUPTREE. If the network structure is different from the group hierarchy, the extended network must be used. In ECLIPSE 100, the standard network can simulate simple pump/compressor, while the extended network can simulate the multi-level compressors and the automatic chokes. The pumps/compressors are simulated using VFP tables with ALQs representing the pump rating or the compressor power.The facilities available in ECLIPSE 300 will be discussed separately later.

There are two different group control procedures in the network options, the standard procedure and the sub-sea completion manifold group control.Group targets and limits can be applied to any group regardless of whether it is part of a pipeline network. A production rate target applied to a group in the network will be met as long as its subordinate wells have sufficient potential. The wells potentials will of course depend on the nodal pressures in the network, since these determine the wells THP limits.In the above example, a target production rate of 10,000 STB/DAY of oil has applied to the group of three wells. The THP limits of each of its wells are set equal to the groups nodal pressure in the network. The standard procedure for group control will apportion the oil rate target among the groups wells in proportion to their oil phase guide rates. By default, wells guide rates are equal to their production potentials. If some wells cannot produce at their allocated rate targets, they will produce as much as they can subject to their own flow and pressure limits, while the remaining wells under group control make up the rest of the groups flow target based on their guide rates.When a well is under group control, if its production potential is higher than the rate target allocated to it, it will be producing at that rate with its THP greater than the groups nodal pressure in the network. This is equivalent to a well choke that chokes back the wells production to meet its target. The THP values of the group-controlled wells in this group are in general all different. When a wells THP reaches the groups nodal pressure, the well is under THP control. From this point, the well cannot produce its allocated rate, and the other wells will make up the rest of the groups target.This is the default group control method in network options.

If a group represents a sub-sea completion manifold, in reality all its wells are operating at the same THP, that is the pressure at the manifold. The standard method of group control by guide rates is no longer appropriate for groups in which all the wells share a common manifold.An alternative method of group control is available in the network options for groups representing sub-sea completion manifolds. This method calculates a common THP required for all the wells to produce at its groups target rate. If the group of wells have higher potential than the groups target, this method applies a choke to the groups outlet flow line, to increase the upstream pressure and reduce the production rate, compared to choking back each well separately in the standard method. The group is able to produce at its target rate as long as the calculated value of its wells common THP remains above the groups (unchoked) nodal pressure in the network. If the calculated THP value falls below the groups nodal pressure in the network, the wells operate at the groups nodal pressure and the group is no longer able to produce its target rate. At this point other actions such as the production rules (see keyword PRORDER), if defined, will be activated to increase the productivity of the group and bring the groups production back to its target rate. This alternative method of group control can be invoked by declaring the group to be a sub-sea completion manifold in keyword GRUPNET or NODEPROP.Since the network starts from the wells tubing head, the THP must be calculated for the wells in the network. To do this, a VFP table needs to be assigned to a producer by item 11 of keyword WCONPROD. ECLIPSE will use that VFP table to calculate the well tubing head pressure. During the simulation with the network options, the wells tubing head pressure will be limited by its groups nodal pressure. The wells tubing head pressure limit defined by item 10 in keyword WCONPROD will be overwritten by the groups nodal pressure. But the THP value input for the first well in the group is used as the initial guess for the manifold groups THP in the first time step. A value near the solution entered for this quantity speeds the convergence of the first calculation.To set up a standard network, the multi-level grouping tree must first be defined using keyword GRUPTREE. Since the network structure is the same as the network structure in the standard network, the pipeline network is defined by GRUPTREE as well. In the above example, the GRUPTREE defines a network with 4 flow lines (GR-A1 to PLAT-A, GR-A2 to PLAT-A, GR-B1 to PLAT-B, GR-B2 to PLAT-B) and 6 nodes (GR-A1, GR-A2, PLAT-A, GR-B1, GR-B2, PLAT-B and FIELD). PLAT-A and PLAT-B are two terminal nodes.A VFP table must be assigned to each flow line to calculate the pressure losses along the flow line. To calculate the pressure at each node, the boundary condition needs to be specified, that is to assign fixed pressures to the terminal nodes. Keyword GRUPNET is used to specify these data for a production network. If a node is not a fixed pressure node, item 2 of GRUPNET is defaulted. When a VFP table (item 3) is assigned to a flow line, the child group node ( item 1) is used to refer to the flow line, e.g. GR-A1 refers to the flow line connecting child group node GR-A1 and parent group node PLAT-A. In the above example, the two terminal nodes are given fixed pressure of 300 psia. Because they are terminal nodes, they do not have parent group nodes as part of the network, so VFP tables and the remaining items are defaulted. Flow line GR-A1 to PLAT-A will use VFP table 1, GR-A2 to PLAT-A will use VFP table 2, and so on so forth. If the pressure loss along a flow line is zero, a VFP table 9999 is specified.An ALQ value (item 4) can be specified for looking up the VFP table. The density of the mixture in the flow line can also be used as ALQ for VFP table look-up (item 7). A well group node can be declared (item 5) as a sub-sea completion manifold so that the group control procedure for sub-sea completion manifold described previously will be applied. In the above example, all the 4 well groups are sub-sea completion manifold groups. Their subordinate wells in a group will have a common THP.Three options are available (item 6) for a group whose subordinate wells use gas lift, on how the lift gas is treated with respect to the calculation of the pressure loss along the flow line between the group and its parent group:NO: No lift gas flows along the pipeline, only gas produced from the formation.FLO: Add the lift gas flows from the subordinate producers to the gas flow rate along the pipeline. The lift gas flow is assumed to be equal to the sum of the lift gas injection rates of the subordinate producers, multiplied by their efficiency factors. The total gas flow rate will be used.ALQ: Set the ALQ value for this pipeline equal to the sum of the ALQ values of the subordinate producers, multiplied by their efficiency factors. This ALQ will be used in the VFP table look-up. The entry in item 4 is ignored.

GNETINJE is used to set up an injection standard network, if required. The injection network is independent of a production network. The keyword defines the injection phase (item 2), the fixed pressure (item 3), and the VFP table (item 4). The group name (item 1) refers to either the the group node whose pressure is fixed, or the flow line between its node and its parent group node. In the above example, a water injection network is setup where a pump is represented by VFP table 2 between node BR-B2 and node PLAT-B. Node PLAT-B is defined as a fixed pressure node with the pumps inlet pressure of 14.7 psia. The injectors under group GR-B2 have their THPs limited by GR-B2s group nodal pressure, that is the outlet pressure of the pump. To make this work, a VFP table needs to be assigned to each injector (item 9 of WCONINJE) for calculating THPs of the wells.The injection network is separate from the production network even they have the same group names, such as PLAT-B and GR-B2. ECLIPSE outputs separate pressures for the injection network and production network for the group with the same name (GPR - group nodal pressure for production network, GPRW group nodal pressure for water injection network, GPRG group nodal pressure for gas injection network). Production targets or limits are set for groups using GCONPROD. If group control is applied to any group superior to a manifold group, the subordinate manifold groups should be given guide rates in keyword GCONPROD, as they are required to calculate the target for the manifold group. When a manifold group has a rate target (either imposed directly or allocated as a share of a superior groups rate target in proportion to its guide rate), ECLIPSE calculates the manifold pressure required to make the group produce at its target rate. The calculation is performed iteratively, using a secant method. The convergence tolerance and the maximum number of iterations allowed for this calculation can be set in keyword NETBALAN. The manifold pressure is recalculated at each of the first NUPCOL Newton iterations of each time step. And the wells THP limits are set equal to the manifold pressure or the groups nodal pressure in the network obtained from the latest network balancing calculation, whichever is the greater. If the time step takes more than NUPCOL Newton iterations to converge, the well THP limits are kept constant for the remaining iterations after the first NUPCOL, and the group may not meet its rate target within the allowed convergence tolerance. If a well group is declared as sub-sea completion manifold, but does not have a rate target (directly or by its guide rate), the standard group control procedure instead of the above procedure is applied ECLIPSE prints out a warning on this in the PRT file. In this case, all the wells may have different THPs. In the above example, the FIELD has a oil rate target 50000 Stb/d. The two platform groups PLAT-A and PLAT-B have water handling capacity of 10000 Stb/d. They are given equal liquid guide rate based on which the field oil target is allocated. The four well groups GR* have been declared as sub-sea completion manifold groups, therefore are given liquid guide rates so that their superior groups can allocate targets to them. The wells that subordinate to each of these groups will operate under a common tubing head pressure.To maintain a groups production above a limit, an simple automatic pump/compressor can be defined using GNETPUMP. This keyword specifies the groups name, the minimum rate of a particular phase, such as oil, below which the pump will turn on. It specifies a VFP table together with a new ALQ value that are used to represent the pump in operation. If the VFP table is defaulted, the VFP table defined in keyword GRUPNET previously will be used. A zero or negative rate limit will turn off the pump. It also specify any gas consumption from operating the pump. The gas consumption is subtracted from the flow rate through the pipeline when interpolating the VFP table to calculate the pressure loss. Gas consumption is also taken into account for group reinjection control (see keyword GCONINJE) and sales gas control (see keyword GCONSALE). But the total gas production rates reported for the groups and the field will not be reduced.The pump/compressor is switched on at the end of the time step in which the groups production rate falls below the limit defined. A network balancing calculation is performed at the beginning of the next time step, regardless of the interval set in keyword NETBALAN. However, if a limit tolerance fraction has been set with keyword WLIMTOL, the time step in which the rate fell below the limit is recalculated with the pump/compressor switched on if the limit is violated by more than this fraction.In the above example, a pump is used to boost the flow through the flow line from GR-B1 to PLAT-B. The pump will start if the oil rate for GR-G1 falls below 500 Stb/d. When the pump is on, ECLIPSE uses an new ALQ of 50 to interpolate the VFP table 3 that is defined in GRUPNET previously.The calculation of nodal pressures of the groups in the network is called network balancing. It uses an iterative procedure to calculate the pressures at each group node in the network consistent with the group flow rates and the pipeline pressure losses. At each iteration of the network balancing calculation the well and group production rates are determined using the reservoir conditions existing at the beginning of the time step, and the the nodal pressures from the previous iteration. The pipeline pressure losses generated by these flow rates are then calculated, and the nodal pressures are updated at each level in the grouping tree from the fixed-pressure node(s) upwards using a secant method. The iterations are terminated when all the nodal pressures agree with the pipeline pressure losses, to within a certain tolerance.At each network balancing iteration, the well and group production rates are determined from the nodal pressures from the latest iteration.By default, the network is balanced using the grid block conditions existing at the beginning of the time step. By the end of the time step, the grid block conditions and well flow rates may have changed, and the flows in the network branches may no longer be exactly consistent with the nodal pressures. The longer the time step or interval between balancing calculations, the greater the balancing error will be at the end of the time step. ECLIPSE 100 checks the balancing error in each branch of the network at the end of each time step, and prints out the largest error in any branch in the PRT file. The balancing error is defined as the difference between the pressure drop along the branch when the network was last balanced, and the pressure drop calculated using the current flow rates at the end of the time step.You can change the parameters that control the network balancing calculation in keyword NETBALAN. You can control the frequency with which the network balancing calculations are performed by specifying the balancing interval. A network balancing calculation will take place at the beginning of the next time step, and again at the beginning of the time step after the specified interval has elapsed since the previous calculation. The nodal pressures are kept constant until updated by the next balancing calculation. A large balancing interval normally results in large balancing errors if the reservoir conditions have changed significantly over the interval. The default value of the balancing interval is zero - a balancing calculation being performed at the beginning of each time step. You can also adjust the convergence tolerance and the maximum number of iterations in the calculation in keyword NETBALAN.Setting the balancing interval negative makes ECLIPSE 100 balance the network in each of the first NUPCOL Newton iterations of every time step. This option, in general, results in much smaller balancing errors at the end of the time step, as the reservoir conditions at each successive Newton iteration more closely resemble the converged conditions at the end of the time step. However, the option may cause the time steps to require more Newton iterations to converge, as the well THP limits vary at each balancing calculation.You can supply a target value and a maximum permitted value for the largest branch balancing error, in the NETBALAN keyword. ECLIPSE 100 attempts to adjust the time step length so as to keep the balancing error at approximately its target value, subject to any other constraints on the time step. If the maximum permitted balancing error is exceeded, ECLIPSE 100 chops the time step and rebalances the network. Since time step chops can severely increase the running time of a simulation, a maximum permitted balancing error should only be used with caution, and its value should be several times larger than the target error. A large balancing error is sometimes unavoidable during the time step in which a well dies. You can set a minimum time step size to prevent a large reduction in step size when wells die.

When the network structure is different from the grouping three structure, the extended network must be used. The network must have a gathering tree structure. In the above example, the top diagram shows the structure of the pipeline network where the FIELD is a fixed pressure node and all well groups feed into the main pipeline at nodes N1, N2, N3,N4. The bottom diagram shows the grouping three where groups GA1 and GA2 belong to company A (group COMP-A), and groups GB1 and GB2 belong to company B (group COMP-B). It can be seen that the group control hierarchy is different form the pipeline network structure, so the extended network instead of the standard network must be used. The extended network is only for production networks in ECLIPSE 100. If an injection network is also required, the standard network should be used for the injection network and the extended network used for the production network. In ECLIPSE 300, the extended network can also be used for injection network, but the standard network cannot be mixed with the extended network. More differences between ECLIPSE 100 and 300 in network options will be discussed later.To set up an extended production network, firstly the group control hierarchy is specified by keyword GRUPTREE, and the production targets and limits are defined for the groups by keyword GCONPROD. The source nodes that inject flow into the network should correspond to groups defined in GRUPTREE with the same names. The source nodes must be those that correspond to well groups, satellite groups, or master groups in reservoir coupling. In the above example, well groups GA1, GA2, GB1, GB2 are source nodes. They have the same names in GRUPTREE as in the network definition which will be described later.The FIELD is given a oil rate target of 50000 Sb/d. The two sub-groups have water production limits of 10000 Sb/d, and the four well groups are assigned equal liquid guide rates. Secondly, the dimensions of the network are defined using NETWORK keyword in the RUNSPEC section. NETWORK specifies the maximum number of network nodes and maximum number of branches (flow lines between nodes) in the model. In the above pipeline network, there are 8 flow lines and 9 nodes.This keyword also turns on the Extended Network Model facilities.Thirdly, each branch is given a VFP table that is used to calculate the pressure loss through the branch. Keyword BRANPROP is used to define a branch by the inlet node (item 1), and outlet node (item 2), the VFP table used for the branch (item 3), the ALQ value (item 4), if any, for looking up the VFP table, and whether the mixture of the fluid is used as ALQ (item 5). In the above example, VFP table 3 is used for branch with inlet node GB2 and outlet node N4. If a branch is assigned VFP table 9999, the pressure loss through the branch is zero. This is useful when a physical node needs to be split into two. For instance, in reservoir coupling well group GA1 cannot be a slave group. It can be split into two nodes, GA1 and N1. GA1 is the original well group, and N1 is a slave group node. A VFP table 9999 assigned to branch GA1-N1 gives zero pressure loss between GA1 and N1, effectively making them the same physical node. Pressures at nodes are calculated based on the pressure losses through branches starting from the fixed pressures at the terminal nodes. NODEPROP keyword is used to specify the properties for special nodes (item 1), such as fixed pressure nodes (item 2). It is also used to declare whether a node is corresponding to a sub-sea completion manifold group or the inlet of an automatic choke (item 3) and the group whose target is controlled by the choke (item 5). If a node corresponding to a well group is set to YES by item 3 of NODEPROP, the sub-sea completion manifold group control procedure will be applied. If a node corresponding to a non-well group, the nodes outlet branch acts as an automatic choke. A production rate target applied to the group named in Item 5 will be met by adjusting the pressure loss across the choke.The keyword also has a flag (item 4) that specifies whether the lift gas from subordinate wells is included in the gas flow rate that is used for VFP table look-up. If the flag is YES, the lift gas flows of the subordinate producers will be added to the gas flow entering the network at this node. The lift gas flow is assumed to be equal to the sum of the ALQ values of the subordinate producers, multiplied by their efficiency factors unless instructed otherwise in WEFAC Item 3. The ALQ variable for the wells must therefore be defined as the rate of lift gas injection. This definition must be used in keyword VFPPROD, and selected in the VFPi program if it is used to generate the VFP tables.Gas may be consumed from the pipeline to power a compressor for example. The removal of gas from the pipeline will affect the pressure loss through the downstream branches. Keyword NCONSUMP is used to specify a constant gas consumption rate (item 2 ) at a particular node (item 1) in the Extended Network, and optionally to assign the consumption also to a group (item 3) in the GRUPTREE hierarchy. It may be used as an alternative to the GCONSUMP keyword when the Extended Network Model is used (keyword NETWORK, in the RUNSPEC section).In the above example, 20 MScf/d gas is consumed from node N1. This amount of gas is removed from group COMP-A.For a constant consumption rate, NCONSUMP and GCONSUMP are equivalent and either of them can be used. However, there are some differences between the two keywords: NCONSUMP allows only a constant consumption rate, while GCONSUMP also allows a consumption rate that is a fraction of the groups production, and also a gas import rate. The two keywords have different defaults for assigning consumption to group/network. If consumption is declared at a source group in GCONSUMP, by default it will also be assigned to the corresponding source node of the network. However, if consumption is declared at a source node in NCONSUMP, by default it will not be assigned to the corresponding group. NCONSUMP may only be used with the Extended Network model. GCONSUMP may be used with either the Extended or Standard models.Automatic compressors or pumps are defined with keyword NETCOMPA instead of GNETPUMP. Each compressor/pump is located at a specified branch of the network. They offer a much wider range of features than the GNETPUMP compressors in the standard network model. NETCOMPA defines an automatic compressor between the inlet node (item 1) and the outlet node (item 2). The compressor is used to maintain a groups (item 3) target rate for a phase (item 4). The compressor can have single level compression (TEMP or PERM in item 9), or multi-level (item 10 defines the number of levels) compression (MULT in item 9). The compressor is represented by a VFP table (item 5) with the ALQ value at level one compression (item 11), and the ALQ value at the full level (item 6). The keyword also defines the gas consumption at full level (item 7) from a particular group (item 8). Each compressor can have a sequence number (item 12) which determines the order in which the compressors are turned on. If the target group (item 3) is defaulted, the compressor is permanently off. In the above example, a 3-level compressor is defined between node GA1 and N1 to maintain the gas production target for group COMP-A. The VFP table defined for this branch in BRANPROP together with the ALQ values (100 on 3 levels, 40 on 1 level, interpolated values on level 2) will be used to calculate the pressure loss through the branch. 500 Mscf/d gas will be removed from the branch and from group COMP-A when the compressor is on 3 levels. A single level temporary compressor is defined between node GB1 and node N2 to maintain the gas production target for group COMP-B. The pressure loss through the branch is calculated by looking up the VFP table 3 ( that is defined in BRANPROP in previous slide) using ALQ=50.

Activated by group target - Each compressor (or pump) is turned on whenever a nominated group fails to meets its gas (or oil) production rate target or its share of the higher level groups production target.Compressor switching sequence - It is possible for more than one compressor to respond the same group. Each compressor can be given a sequence number, and when the group fails to meet its production target the compressors that responds to the group will be activated in increasing order of their sequence number. All compressors in the network that share the same sequence number are turned on simultaneously.Production rule order - If there is a drilling queue (keyword QDRILL), by default ECLIPSE scans it for a suitable well to open in preference to switching on a compressor when a group cannot meet its production target. However, by using the PRORDER keyword with 'COMP' being placed before 'DRILL, ECLIPSE activates the automatic compressors before looking for a new well to open.Multi-level compression - Multi-level compressors can be defined. Compression is increased one level at a time until the nominated group can meet its production target. The ALQ, and the gas consumption rate if there is any, increase linearly with the level number to their full on values. Any number of levels may be requested, but having a large number of levels slows the run down as each level must be tried in turn by re-balancing the network.Turning compression off - Compressors can be turned off (or reset to zero compression) manually at any time by using the COMPOFF keyword. They are turned on automatically again as soon as they are needed. For example, the COMPOFF keyword can be entered whenever the target production rate is reduced, or when extra production capacity is added. (When using the Gas Field Operations model, the compressors are turned off automatically whenever the contract groups target rate decreases.) COMPOFF has no effect on permanent compressors.An automatic choke is an alternative means of controlling a groups production rate when using the Extended Network option. It is distinct from guide rate control or prioritization. The choke is placed in a designated branch of the network, and at each network balancing iteration ECLIPSE adjusts the pressure loss across it to keep a specified group producing at its target rate. The operation of the choke varies the pressure in its inlet node, which in turn affects the productivity of the subordinate wells while they are operating under THP control.A branch is defined to be a choke by answering 'YES' to Item 3 of the NODEPROP keyword for the inlet node of the choke. The only pressure drop allowed across a branch acting as a choke is that caused by the action of the choke itself. The branch should therefore be declared in the BRANPROP keyword with a VFP table of 9999. Any other table number is flagged as an error.In the above example, an automatic choke is defined between node NCHOKE and FIELD to control the production for FIELD by varying the inlet pressure at node NCHOKE. Sine the pressure drop across the choke is purely from the choke, a VFP table 9999 is given for branch from NCHOKE to FIELD.An automatic choke works in a similar way to a sub-sea completion manifold. When the groups rate is larger than its target, ECLIPSE increases the inlet pressure to choke back the production. When the groups rate is less than its target, ECLIPSE decreases the inlet pressure to increase the production. When the pressure drop across the choke reaches zero, the choke does not have control any more the group cannot meet its target. Other actions need to be taken, such as drilling new wells defined in PRORDER, to increase the groups production.A fixed-pressure node cannot be defined as a choke inlet node, since its pressure cannot respond to the chokes pressure loss. Also, source nodes cannot be defined as choke inlet nodes. Well-group source nodes can instead be designated to be manifold groups, whose operation is similar to choke inlet nodes in that ECLIPSE determines a common well THP that makes the group meet its target rate.The wells subordinate to the choke respond to the choke pressure drop whenever they are operating under THP control. Thus, for the automatic choke to work correctly, its subordinate wells must be made to ignore any rate targets set for them by guide rate group control. Accordingly, ECLIPSE 100 automatically makes them unavailable for guide rate group control (this is not necessary in ECLIPSE 300), equivalent to setting Item 2 in the WGRUPCON keyword to NO'. This is done for all producers in source groups subordinate to the choke, as long as there is no intermediate fixed-pressure node between the source group and the choke. The wells can still be given individual flow rate and BHP limits with keyword WCONPROD, which causes them to come off THP control if they are violated. If a producer subordinate to a choke is subsequently turned into an injector which is subject to group injection control, you must make the well available for group control again by entering the WGRUPCON keyword with 'YES' in Item 2 at the time that the well is redefined as an injector.The following summary vectors that are related to network options can be requested in the SUMMARY section:GPR - Group nodal pressureGPRG - Group nodal pressure in the gas injection networkGPRW - Group nodal pressure in the water injection networkGPRB - Pressure drop along the groups outlet branch GPRBG - Pressure drop along the groups inlet branch in the gas injection networkGPRBW - Pressure drop along the groups inlet branch in the water injection networkGALQ - ALQ in the groups outlet branchIt can be seen that the injection nodal pressure is different from the production nodal pressure even for the node with the same name.

The following information is written into the print (.PRT) file:The tree structure of the networkGROUP LEVELSHIERARCHICAL DESCRIPTION OF GROUP CONTROL STRUCTURENETWORK OPTION DATA

For example, the output for the network structure in the PRT file looks like:

HIERARCHICAL DESCRIPTION OF EXTENDED NETWORK STRUCTURE------------------------------------------------------FIELD | |---PLAT | |---PL-B | | | |---SC-C | |---SC-B | |---PL-A When wells tubing head pressures are equal to the groups nodal pressures, the production rate through a pipeline is limited by the fixed pressure at the terminal node of the pipeline. GNETDPT may be used to adjust the pressure of a fixed-pressure group or node in the Network option with the aim of maintaining its production flow rate within specified maximum and minimum limits. Whenever the flow into the fixed-pressure group or node falls below the minimum rate (item 3), ECLIPSE adjusts its pressure value by subtracting a pressure increment (item 5), then rebalances the network. This process continues until either the flow exceeds the minimum value or the pressure falls to the minimum allowed pressure (item 7). Similarly, whenever the flow into the fixed-pressure group or node rises above the maximum rate (item 4), ECLIPSE adjusts its pressure value by adding a pressure increment (item 6), then rebalances the network. This process continues until either the flow falls below the maximum value or the pressure increases to the maximum allowed pressure (item 8).COMPOFF can be used to switch off the automatic compressors that is defined in the extended network NETCOMPA) and in the gas field operations (GASFCOMP).NWATREM is used to remove water from a node in the extended network. The rate of the water removed is subject a maximum rate and a maximum fraction of the water flow through the node.The water removal only affects the pressure losses in the downstream braches, so the node must have outflow branch. WAITBAL is used to tell ECLIPSE to take actions defined in PRORDER and GDRILPOT after a network is balanced. The reason for this is that it is possible that during the network balancing, an intermediate balancing iteration with high nodal pressures and consequentially low well productivities may cause such an action to be taken prematurely. This can be prevented by using the WAITBAL keyword to request that these actions should not be performed until the network is properly balanced. Then if more flow is required once the network has converged, an appropriate action is performed and the network must be balanced again.When the efficiency factors of wells are defined by WEFAC, there are two choices on whether a wells efficiency factor will be included when calculating the branch flows and pressure losses in the Extended Network option:YES - The extended network branch pressure losses is calculated using the wells time- averaged flow rate (that is the well rate multiplied by its efficiency factor).NO - The extended network branch pressure losses is calculated using the wells full flow rate (that is the well rate not multiplied by its efficiency factor).This flag applies only to the Extended Network Model. If the Standard Network Model is used, the time-averaged well flows are always used to calculate the branch pressure losses.Similarly, when GEFAC is used for a group, there are two choices on whether the groups efficiency factor will be automatically transferred to its corresponding node in the Extended Network option:YES - The nodes flow contribution to the flow rate of its parent node in the network will be multiplied by the groups efficiency factor. Thus the branch pressure losses downstream of the parent node reflect the time-averaged contribution of this group. But the pressure losses in the outlet branch of this groups node still reflect the full, or reported, group flow rate.NO - The nodes contribution to the flow rate of its parent node in the network is not multiplied by the groups efficiency factor. Thus all downstream branch pressure losses reflect the full flow rate of this group.This flag applies only to the Extended Network Model. If the Standard Network Model is being run, the groups reported flows are always used to calculate the pressure losses in the branch to their parent group. The flag also applies only if there is a node in the extended network that has the same name as the group. Otherwise, the NEFAC keyword can be used to apply efficiency factors directly to the network nodes.NEFAC may be used to specify an efficiency factor at a node in the Extended Network. This may be useful if a group efficiency factor has been applied with keyword GEFAC to a group which does not correspond to a network node; NEFAC may then be used to apply the efficiency factor to an appropriate node in the network, if desired. Alternatively it may be used to set a nodes efficiency factor, which governs its contribution to downstream nodes in the network, to a value different from the efficiency factor that has been set for its corresponding group with keyword GEFAC.Care should be taken if you are also using the GEFAC keyword with item 3 set to YES, if the node name and the group name are the same. If GEFAC is entered after NEFAC then the nodal efficiency factors gets reset by GEFAC. On the other hand, using NEFAC does not change a groups efficiency factor, even if it has the same name as the node. The efficiency values assigned to the groups/nodes can be checked by using the WELSPECS mnemonic in the RPTSCHED keyword.WNETDP is used to to apply an additional fixed pressure drop between a well's tubing head and its group's corresponding node in the network. Normally the wells' THP limits are set equal to their group's nodal pressure at each network balancing calculation. But if a fixed pressure drop is specified with this keyword (item 2) for a well (item 1), the well's THP limit is calculated as follows:for a production well in a production network,well THP limit = groups nodal pressure + fixed pressure drop for wellfor an injection well in an injection network,well THP limit = groups nodal pressure - fixed pressure drop for well.The keyword can also be used to isolate individual wells from the effects of the network. If the fixed pressure drop is set to a value greater than or equal to 1.0E10, the well's THP limit remains unchanged by the network balancing calculation and is not set equal to its group's nodal pressure. The well's flow, however, is still added to the network flows.WAITBAL is used to tell ECLIPSE to take actions defined in PRORDER and GDRILPOT after a network is balanced. The reason for this is that it is possible that during the network balancing, an intermediate balancing iteration with high nodal pressures and consequentially low well productivities may cause such an action to be taken prematurely. This can be prevented by using the WAITBAL keyword to request that these actions should not be performed until the network is properly balanced. Then if more flow is required once the network has converged, an appropriate action is performed and the network must be balanced again.WNETCTRL can be used to select the well control quantity that is held constant after the network has been balanced and until the next balancing calculation. Normally this quantity is the well THP limit, which is fixed equal to its groups nodal pressure in the network. By default, this will be the network control quantity for all the wells if the WNETCTRL keyword is absent.If GRAT is selected as the well control quantity for example, the network will be balanced as usual by setting the wells THP limits from their groups nodal pressure. However, any wells constrained by the network (i.e. that are under THP control in the balanced network) will have their gas flow rate limit fixed at its current value until the next network balancing calculation, and their THP limit removed. Any gas flow rate limit set by the user will still be honored, if ever that becomes the acting constraint. This may be the case in high-permeability gas reservoirs with compressors in the network where gas rate is maintained, but the pressure are very sensitive to the rate.

OPTIONS(33) sets the number of network balancing iterations in which a well can be revived after being closed because it cannot operate against its current THP. If set = 0, this defaults to max (4, NETBAL/2) where NETBAL is the maximum number of network balancing iterations allowed (item 3 in the NETBALAN keyword ).OPTIONS(57) During the iterations for calculating the automatic chokes pressure drop in the extended network, it is possible that the changes in wells THPs are sufficient for all the wells to die together. By default the wells zero flow THP is calculated by assuming all well variables are fixed, including the BHP, and then calculating the THP at which a zero flow is obtained. In fact, BHP increases when flow rate is decreased. The wells would not have had died if the change in BHP were considered. If set this switch to 1 then ECLIPSE calculates the actual THP at which the well would die, now only assuming that the water-cut, gas fraction etc. of the well remain constant.So far we have mainly discussed network options in ECLIPSE 100. While most of the facilities are available in ECLIPSE 300, there are several important differences between ECLIPSE 100 and ECLIPSE 300. Below are the major differences:In E300:No sub-sea completion manifold group control is available for well groups. It uses automatic choke to apply rate constraints at any level of the network, in both standard and extended network.Standard network and extended network cannot be mixed.It can use extended network for injection network. It allows to use automatic choke in the injection network. Source node name can be different from its corresponding group name in the extended network.The network is always balanced in each of the first NUPCOL Newton iterations of every time step. (This is equivalent to setting a negative balancing interval in ECLIPSE 100.)WAITBAL is activated by default Automatic pump/compressor facility is not availableFuel gas can be removed from a node NGASREM

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