A Preconditioned Adaptive Implicit Method for Reservoirs with Surface Facilities

The formulation of a black-oil or compositional fully coupled surface and subsurface simulator is described. It is based on replacing the well model in a conventional reservoir simulator with a generalized network model of the wells and facilities. This allows for representation of complex wellbore geometry and downhole equipment. The method avoids the inefficiencies and/or inaccuracies of other coupled models, in which wells and facilities are treated as separate domains or in which the global system is not solved simultaneously. Example cases demonstrate the performance of the model for cases with simple and segmented wellbores (with and without facilities).

Section: Conventional Well Model a Basic Example Of Domain Decomposimentioning

confidence: 99%

A Generalized Wellbore and Surface Facility Model, Fully Coupled to a Reservoir Simulator

Coats

Fleming

Watts

et al. 2004

“…Zapata et al (2001) investigated the use of an iteratively (reservoir-network) updated implicit bottomhole pressure to reduce the oscillations. The instability of a coupled system is also a cause of excessive computational time if separate models are solved iteratively (Coats et al 2004). Schiozer and Aziz (1994) investigated applying domain-decomposition techniques to well subdomains to accelerate iteratively coupled simulation.…”

Section: Introductionmentioning

confidence: 99%

“…By "fully implicit," we refer to the coupling of the reservoir and network as a single set of equations and the simultaneous solution of the combined equation set at each Newton iteration. Coats et al (2004) and Shiralkar and Watts (2005) presented different combined formulations on the basis of extending the existing reservoir-simulation equations to include network-model equations.…”

Section: Introductionmentioning

confidence: 99%

A Semi-Implicit Approach for Integrated Reservoir and Surface-Network Simulation

Liang¹,

Rubin²

2014

Conventionally, methods of coupling reservoirs and surface networks are categorized into implicit and explicit approaches. The term "implicit coupling" indicates that the two simulators solve unknowns together, simultaneously, or iteratively, whereas "explicit coupling" indicates that the two simulators solve unknowns sequentially and exchange their boundary conditions at the last coupled time t n .The explicit approach is straightforward to implement in existing reservoir and surface-network models and is widely used. Explicit coupling does have drawbacks, however, because well rate and pressure oscillations are often observed.In this paper, a new semi-implicit method for coupled simulation is presented. This technique stabilizes and improves the accuracy of the coupled model. The "semi-implicit coupling" overcomes the problems found in explicit-coupling methods without requiring the complexity of a fully implicit coupled model.The new approach predicts inflow-performance-relationship (IPR) curves at the next coupled time t nþ1 by simultaneously conducting well tests for all wells in the reservoir before actually taking the required timestep. All wells first flow simultaneously to the next coupled time t nþ1 with the well rates unchanged from the last coupled timestep. The timestep is rewound, and all well rates are reduced by a uniform fraction and then simultaneously flow again to t nþ1 . By extrapolating the resulting well pressures, the well's shut-in pressures at time t nþ1 are determined, and thus, straight-line IPRs are produced. The new IPR curves approximate better each well's drainage region at t nþ1 and each well's shut-in pressure at t nþ1 which helps to stabilize the explicitly coupled model.The new coupling technique normally does not require iteration between the reservoir and surface network and normally has the stability and accuracy characteristics of an implicitly coupled approach. Because the well tests already account for individual well-drainage regions, an explicit knowledge of the well-drainage region is not required. Because of the stabilized IPR, the approach also was found to reduce the overall computational time compared with explicit coupling.Applications of the new approach are presented that show significant improvements surpassing explicit coupling in both stability and accuracy. IntroductionIt has been widely recognized that when reservoir-deliverability forecasting and surface-network planning are required, integrated reservoir and surface-network simulation can provide more-realistic results than separate models of the reservoir and surface network. During the last 40 years, different methods to couple reservoir and network models were developed and studied by a number of investigators. Dempsey et al. (1971) first presented a technique that iteratively solved reservoir, tubing-string, and gathering system models to accurately evaluate gasfield deliverability. The concept was extended to the black-oil system by Startzman et al. (1977), and the scheme was modified by Emanuel and ...

“…The near-well subdomains are included in the iterative balancing process. Byer et al (1999) also investigated the use of near-well subdomains in preconditioning a fully coupled system.…”

Section: Introductionmentioning

confidence: 99%

Near-Well-Subdomain Simulations for Accurate Inflow-Performance-Relationship Calculation To Improve Stability of Reservoir/Network Coupling

Güyagüler

Zapata

Cao

et al. 2011

Externally coupled workflows that rely on exchanging inflowperformance relationships (IPRs) at the coupling points, such as those between reservoir and surface-network simulators, may exhibit oscillations because of the IPR calculated at the beginning of a timestep not being representative of the IPR at the end of the timestep. One solution is to have an implicitly coupled reservoir/surface system. This is often impractical because the reservoir and the surface network may be modeled using different applications, or the resulting coupled system may become too large and too complex to solve implicitly because of processing time and convergence issues. We propose the calculation of multipoint IPRs obtained by solving near-well subdomains for the subsequent timestep. A flexible reservoir-simulation architecture enables the dynamic creation and simulation of near-well subdomains at run time. Subdomains are created automatically within the vicinity of the well or may be defined dynamically from the pressure gradient. These near-well-subdomain simulations are embedded within the full-field simulation and extract all the required model properties (pressure/volume/temperature, rock) from the full-field model. The most recent fluxes from the global solution are used as boundary conditions for the near-well subdomains. In this paper, the subdomain IPRs are used within reservoir/network coupling workflows for which traditionally calculated IPRs result in oscillations and high errors. Sensitivity analysis is carried out on the extent of the subdomains and the size of the coupling timestep. A real field case is used to show that subdomain IPRs result in smooth pressure/ rate profiles as opposed to the oscillatory profiles obtained from explicitly calculated IPRs and that they also help reduce balancing errors between reservoir and surface models.