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Material balance models in production forecasting
Whenever we make a production forecast, we use a model of the reservoir and production system, whether it be in the form of a simple mathematical equation (e.g. decline curves) or a full-field 3-D simulation model with surface networking. But no matter how complex the model, it is always a simplification of reality. The aim of the forecaster, in making reliable predictions, is to use a model that is sufficiently representative of the physical processes and constraints, and that adequately allows, on a resource-benefit basis, for treatment of uncertainty in the input and output of the model.
Somewhere in the spectrum of modelling techniques, material balance plays an important role; either in supporting a more complex model (e.g. ground-truthing results) or as the principal methodology for producing forecasts. Material balance treats the reservoir as a tank (or limited number of tanks) with uniform properties. Other than what is required to calculate volumes, there is limited geological input. This lends simplicity and practicality but at the same time limits the applicability in more complex reservoirs. This chapter describes the potential uses of material balance, when to use the technique and offers practical guidelines on its use.
What is material balance
General description of the technique; inputs and outputs, what can and can’t be modelled. Vertical Lift / Surface networks.
Uses of material balance
Reservoir performance, performance-based verification of reservoir / aquifer / gas cap volumes,
When to use material balance
With the increased capability of and accessibility to high-powered CPUs, the default option of the reservoir forecaster today is to build a 3-D simulation model. Whilst this often gives the impression of rigour and can look impressive to the less scientifically-inclined, the use of a simulation model may be overkill. It requires additional input that may not add to the representativeness of the model and, furthermore, may not be supported by reliable / available data. At the same time, this modelling route invokes a significantly increased resource and time cost that may detract from producing a reliable forecast. Material balance should always be considered early as a modelling option on the route to generating production forecasts.
Based on complexity of reservoir (permeability variation), complexity of reservoir fluid system ( oil vs gas, single vs multiphase) and complexity of development plan. Data availability (geological and performance data) and uncertainty. Time/resources availability. Is surface network modelling (e.g. in a gas-field complex) the most important determinant in production performance?
INSERT Reservoir Heterogeneity (Pending permission approval)
Forecasting guidelines using material balance modelling
Summary guidelines on how and when to use. List of 10 to 15 bullet points