Production Modeling and Optimization

This document presents an overview of the capabilities and expertise of eP's Production Optimization group, and describes the scope of some recent projects. eP seeks to deliver high value training and consulting services through the continuous development of petroleum engineering expertise, and business partnering, providing customers with real and tangible benefits such as:

• Maximizing asset value through expert evaluation and optimization
• Development of production and development strategies
• Cost and time saving

What is Production Optimization?

In order to optimize the value of an asset it is necessary to understand the performance of the system by integrating the models of the components in an integrated well or field production system model. Firstly, a model is built using eP's WellFlo or ReO software that is calibrated to the measured performance of the reservoir inflow and production gathering system. ReO is an advanced integrated production system optimization and simulation software package. WellFlo is a combination of WellFlo and FieldFlo which model well performance and production networks respectively. This model can then be used to optimize the system by modeling the effects of changes in the reservoir inflow performance, produced fluids, and production system parameters for a single well or a complete field.

The system components included in WellFlo models are:

Well Inflow Evaluation

The reservoir deliverability or inflow performance relationship (IPR) is the first component necessary to build a system model. This is modeled effectively in the eP software by constant PI, Fetkovitch, Vogel, or Normalized Pseudo Pressure IPRs. NPP is a rigorous method developed for use by eP which models multi-layer systems fully defined by reservoir fluids and relative permeability data.

The selection of the correct curve is critical in matching and predicting the inflow performance under varying conditions of draw down, fluid and gas ratios, reservoir depletion, vertical effective stress, relative permeability, and wellbore skin. WellFlo can model the benefits of skin reduction, and water shutoff programs in multi-layer systems.

If required eP also provides market leading well test analysis software in PanSystem so that the results of transient test analysis can be incorporated into the IPR model in WellFlo.

Completion Design and Performance

The performance of the production string is modeled by generating a vertical lift performance (VLP) curve which combines with the IPR to define the total well performance. The VLP curve generated by WellFlo for each well defines the pressure and temperature changes with depth for a particular completion string under a set of flow parameters, PVT conditions, FTHP and tubing restrictions.

This model can be tuned to match in-situ flow meter and production gradient surveys. A tubing flow model is found which matches measured performance and allows prediction of well performance with changes in BHP, FTHP, GLR, and GOR.

Performance analysis entails looking at changes in performance and deciding whether those changes are due to factors outwith the control of the operator, such as depleting reservoir pressure and increased water cut or whether they might be due to completion problems. This can be analyzed if inflow and outflow is correctly characterized by WellFlo so that normal and abnormal changes can be differentiated. Optimization of the production system is then achieved by predicting the effects of changing tubing sizes, tapered strings, and restrictions such as SSSVs, packers, and tailpipes.

Artificial Lift Design

Design of an artificial lift system entails prediction of the effect of artificial lift on well performance and selection of components of an artificial lift system. The main artificial lift methods are:

• Gas lift
• Electric submersible pump (ESP)
• Jet pumping
• Beam or rod pumping
• Hydraulic pumping

Gas lift and ESP pumping are modeled by WellFlo, with an additional jet pump prediction option currently in preparation. These three methods cover high volume applications, typical of offshore developments.

Well and Field Gas Lift Optimization

Where a gas lift system is installed or is planned to be installed, it has to be continuously optimized to maximize production. This means the optimum volume of lift gas to each well and the optimum pressure of the gas compression system has to be calculated. Too much or too little lift gas will reduce the profitability of the well. On a field wide basis, the distribution and redistribution of gas to wells is a continuous operation. If a well is being worked over, its gas allocation can be temporarily re-deployed elsewhere. Also, if there is a shutdown, the optimum start-up sequence has to be determined.

Surface Network and Facilities Interface Optimization

The surface network, that is the wellheads, chokes, flow lines, and manifolds have to be optimally designed to prevent a bottleneck in the production system. However, the key is not to design for peak rates but to provide a design which will be optimal over a period of time. WellFlo and FieldFlo provide such a surface network design.

The facility design parameters which have most impact on well and reservoir performance are the first stage separator pressures, which determine the back pressure on the production system, and the capacities of the oil production, water handling, gas handling, gas compression, and water injection equipment. These all need to be recognized in the optimization algorithm. WellFlo allows accurate well characterization via VFP tables for reservoir simulation to provide accurate predictions with time. WellFlo also predicts temperatures of the flowing stream and flow regimes. The flow regime of the fluids as they enter the inlet manifolds must be characterized, so that instabilities of flow which may impact facility performance are identified.

Lift Curve Generation and VFP Table Output To 3D Simulators

VFP Tables, also often called Wellbore Hydraulics Tables, are necessary as input data for 3D simulation. They consist of an array of bottom hole pressures (inflow pressures) produced by WellFlo for a given tubing size at different combinations of flow parameters, namely flow rate, FTHP, water cut, GOR, and gas lift injection rates. Input of the VFP array allows the simulator to determine the operating point of any well for the particular completion design at all stages of the field's life.

A typical 3D model study will prepare a field production profile for the field within which the planned well is included. Well and field production profiles are then built up for a range of investment opportunities, for instance installing gas lift, installing a larger tubing, increasing compressor capacity to provide more lift gas, or modifying production facilities to provide a reduced FTHP. The incremental profiles are then subject to economic analysis with the costs involved to provide a net present value for each project acceleration option.

Production Optimization Methodology

Although the scope of study and output of any project is tailored to meet client's requirements, the methodology behind eP's approach to a typical production optimization study can be summarized as follows:

1. A model for each well in the field is constructed using WellFlo. This includes completion type, tubing type, gas lift valves, reservoir and fluid properties, etc.
2. The inflow/outflow performance of each WellFlo model is tuned to match test data, such as flowing gradient surveys and test separator data.
3. A FieldFlo model is then constructed to link the wells and surface pipelines together. The model can include details of the field gathering system and manifolds, such as the flow lines from each well to a platform header, flow lines from outlying platforms to central facilities, and the flow lines on central facilities. The model can include gas lifted, artificially lifted, and naturally producing wells.
4. The FieldFlo model is then tuned to reported wellhead and manifold pressures and to total hydrocarbon production.

The final model is then used to optimize the production. Optimization criteria are usually defined for maximum oil production, minimum gas production, or optimum revenue. eP's software tools can be used to apply complex real world constraints at any part of the network. Optimization can be applied to management of existing fields or to create production strategies for future asset development.

Recent Production Optimization Activities

A list of eP recent projects can bee seen on the Production Optimization Projects page.