SIMULATION MODEL RUNSPEC Section – Part 1/5

The Volve field simulation directory has ECLIPSE and CMG simulation software input files. In this article, we’ll describe the first part of the ECLIPSE simulation model (VOLVE_2016_EXPAND.DATA) which includes an overview on the simulation run specifications [RUNSPEC]
They build the Volve simulation Model on 680 x 400 total cells with runs distributed on a machine with 4 parallel cores. It simulates a black oil fluids model, starting from 31 Dec 2007, using the 6 production wells and 2 injection wells. We describe all details of the keywords written in the Data file of the model below, an exhaustive description for those who wants to understand the reservoir simulation model.

RUNSPEC

PARALLEL
4
 /

We first instruct the Simulation engine to prepare the Software/ Hardware computing method of 4 cores run on a distributed way. This means that for each calculation step, the software divides the simulation grid, i.e. the set of linear equations, into 4 sections which are solved separately on each CPU core and then the results are matched, this uses the Message Passing Interface Library of Intel®

A finite element reservoir simulator solves a set of linear equations at each time-step to calculate the pressure at each cell.

TITLE
2010a Volve simulation model

The simulation run title is used to name the files for visualization tools / modules.

DIMENS
108 100 63 /

The keyword DIMENS books a set of matrix X, Y, Z for calculation with the required number of cells 108x100x63 = 680 400 cells.

OIL
WATER
GAS
DISGAS
--VAPOIL

Setting the Oil, Water, Gas and dissolved gas, keyword instructs the simulation engine to use the adequate set of equations for each phase, in this case, a black oil reservoir fluid model.
Vaporized oil in the gas phase is canceled as “–” sign precedes it.

METRIC

The unit system used is metric units system.

WSEGDIMS
2 100 4 /

The Multi-segment wells number allowed in this simulation model is 2 and the number of the segment is 100 with 4 allowed branches per multi-segment well.

Multi-segment well models provide detailed well-bore simulation. These are used to model horizontal, multilateral wells, inflow devices, pipeline networks and fracturing.

EQLDIMS
--ntequl ndprvd ndrxvd nttrvd nstrvd
12 100 21 1 20 /

Equilibrium tables dimensions describes the size of the Pressure, Temperature, vaporized oil and gases versus depth tables.
We define 12 equilibrium regions. For each table 100 pressure vs depth nodes points can be used and 21 for the remaining variables (Temperature, vaporized and dissolved oil-gas ratio, temperature, bubble pressure.) One tracer concentration table versus depth with 20 nodes.

EQLOPTS
'THPRES' 'QUIESC' 'MOBILE' /

Threshold pressure activates the threshold option, which dictates a pressure value to initiate the flow between regions. This prevents flow between equilibration region until potential difference exceeds a threshold value.
We apply quiescent equilibrium method to ensure a steady state solution
We also activate the saturation end points correction for the mobile phase (oil, gas & water). It is useful for modeling reservoirs which contain an initial depth variation of either the connate or critical saturations for one or more of the phases present.

ENDSCALE
-- ntendp nsendp
'NODIR' 'REVERS' 1 20 /

Activating the end point saturation table scaling with no sensitivity to direction (x, y or z) and reversible relative permeabilities values for both direction (backflow, forward flow). 1 table with 20 points maximum is allowed.

FAULTDIM
48096 /

The maximum number of fault segment is 48096 for Volve model.

TABDIMS
--ntsfun ntpvt nssfun nppvt ntfip nrpvt notused ntendp
2 12 100 100 30 40 /

We allow for 2 different saturations and 12 PVT tables to be defined, with 100 saturation and pressure points (nodes) as maximum size, 30 Fluid in place regions which were needed for history matching. We use 40 Solubility Rs nodes as we consider dissolved gas in Volve live black oil fluid.

REGDIMS
--ntfip nmfip nrfreg ntfreg mhisim nmhstr ERROR
26 2 1* 26 /

Regions Dimensions defines 26 maximum Fluid in place (FIP) regions with 2 sets of FIP, 1 independent reservoir region is defined “the entire reservoir” and the remaining parameters are defaulted to 1 for Max number of flux regions, enhanced track user defined regions, Coal bed Methane Regions, OPERNUM user-defined regions which allows to multiply the region properties per defined factors, i.e. permeability, double precision and integer arrays, finally 26 polymer flooding mixing regions are allowed.

TRACERS
0 2 /

The number of passive oil tracers allowed is 0, and it allows 2 passive water tracers in this simulation model.

Tracer tracking is used to follow the movement of “marked” fluid elements during a simulation run. Tracers defined to exist in the water phase may be used to determine the movement of water from injection wells or to predict variations in salinity or concentration of other chemical species in the water produced from the reservoir.

WELLDIMS
--nwmaxz ncwmax ngmaxz nwgmax
28 220 7 20 /

An important section is the wells dimensions which defines 28 wells as a maximum number of wells allowed, 220 connection for each well, 7 wells groups can be defined (prod, water injectors, gas injectors etc) and each group can contain a maximum of 20 wells.

NUPCOL
5 /

For each 5 non-linear iteration (time step) to resolve the set of equations, the wells target (Flow rates) are updated.

VFPPDIMS
--mxflo mxmthp mxmwfr mxmgfr mxmalq nmmvft
20 20 20 20 20 5 /

Vertical Flow Performances (VFP) tables for production wells dimensions are :
20 Maximum number of flow rate, tubing head, water fraction, gas fraction and artificial lift quantity values per table
It allows maximum 5 different VFP tables for production wells

VFPIDIMS
--mxsflo mxsthp nmsvft
18 15 5 /

Vertical Flow Performances (VFP) tables for Injection wells dimensions are :
18 Injection flow rate values and 15 tubing head pressure values are allowed, plus we can define 5 different Injection VFP tables.

Vertical Lift / Flow performance (VFP) describes the flow from the bottom hole to the wellhead. The intersection of the Inflow Performance Curve (IPR) and VLF is the operating point, a description of the actual well production.

START
31 'DEC' 2007 /

We set the start date of the simulation model including initialization to be 31st December 2007.

NSTACK
20 /

The size of the stack of previous search directions for the solver (ORTHOMIN or CPR) is 20. Higher numbers lead to better convergence, however, it exponentially increases the memory space needed to simulate the model.

RPTRUNSP

We instruct the simulation engine to report the RUNSPEC parameters to the output file during the simulation; we use it for debugging.

SMRYDIMS
5000 /

Maximum number of vectors to be written to the output file, 5000 is half the default of 10000, which will reduce the enormous quantity of data to be reported, and gain simulation time.

--NONNC

Precedented by “–” the keywords are not active, however, the user might have used this to improve simulation speed. It indicates non-neighbor connections are not allowed in the model.

UNIFOUT
UNIFIN

These two keyword mean that it unifies the input files and the output files, it prevents us from generating many files while running the simulation.

--ROCKCOMP
--REVERS 2 /

Precedented by “–” the keywords are not active, however, it is good to note that the engineer here, tried to use the pressure reversible rock compaction option, probably while trying to history match the reservoir performances.

GRIDOPTS
YES/

The Transmissibility, Diffusivity multipliers options are activated, also this option is useful during the history match process

END OF RUNSPEC