Topic: Petroleum Production Engineering, Well Modeling and Optimization

Applications of Nodal Analysis
The Nodal Analysis approach for optimizing production allows the determination of the producing capacity for any combination of equipment. The effect of changing any component on the total well performance can be easily determined. Some of the useful applications of nodal analysis include:
i. Selecting tubing and flow line sizes
ii. To determine flow rate at which an existing well will produce considering well bore geometry and completion limitations (first by natural flow)
iii. The effect of gravel pack permeability
iv. To evaluate the effect of altering Skin on well productivity
v. To determine under what conditions (which may be related to time) a well will load or die.
vi. To select the most economical time for the installation of artificial lift and to assist in the selection of optimum lift method (Artificial lift design)
vii. Analyze an existing system for abnormal flow restrictions
viii. Analyze the effect of perforating density
ix. To optimize the system to produce the objective flow rate
x. To permit quick recognition of ways to increase production rate
xi. Predicting the effects of depletion on producing capacity
The system Analysis technique has application in both new and old wells. In new wells, the technique can be used to simulate anticipated conditions in order to plan in advance the optimum completion and design. In existing well, the technique is used first to model existing condition, and thereafter to evaluate areas of potential improvements.
In the design and implementation of an efficient producing well system, many of the variables that directly affect the producing capacity of the will can be altered. This flexibility is the basis of the well optimization through system analysis.


Production Process Simulation

Essentially, the production process optimization involves the conventional stages of model characterization, model calibration/Initialization, History Matching, Predictions and Forecasting.
Production Process Simulation involves the mimicking of the actual production process using a computer model to approximate offset well (for new well) or existing well performance. Once the model has been characterized, calibrated and initialized and a base case scenario established; where the observed data matches with the calculated data or the model (within the 0.05% tolerable confidence level), the well can be designed, redesigned and future performance predicted, we can also solve any “what if “ scenario by conducting sensitivity study.

Oil and gas production system performance simulation is done using computer software. Nodal Analysis software are available in the oil and gas industry. Some of the known software include: SAM, PROSPER, FEKETE, PERFORM, PIPESIM, WEM and WePS/HORVIP (SPDC proprietary software). Other industry wide or proprietary models may also be in existence. However and more importantly, each of these models is based on the nodal analysis approach and involves similar analysis or simulation procedure. Hence, they are referred to as Nodal Analysis software. The difference may only be a matter of functionality and flexibility. Thus, each of these models has the same operational principles.
In production process simulation, each component in the entire system is modeled using various equations or correlations to determine the pressure loss through that component as a function of flow rate. The summation of these individual losses makes the total pressure losses through the entire system for a given flow rate. This total loss is ultimately realized as the overall difference between reservoir pressure and the separator pressure. Below are some of the software:
SAM = System Analysis Model
PROSPER = PROduction and System PERformance Modeling
PERFORM = Production PerFORformance Modeling
WEM = Well Evaluation Model
PIPESIM = Well Design & Production Performance Analysis
WePS/HORVIP= Well Performance Simulator/HORiozontal & Vertical Inflow Performance

Model Initialization/Calibration
1. After describing the production system, select the node. If initial data is BHP data select well bore node. If wellhead data, select wellhead node. Select the appropriate IPR model.
2. If we have pressure survey data, run pressure gradient survey to match data, if not run on systems analysis.
3. Sensitize on well bore correlations and select the correlation that gave the closest match.
4. Thereafter, sensitize on GOR to fine tune the match until an acceptable match is obtained. We can also sensitize on other key sensitive parameters such as formation permeability, gravel pack permeability etc.

5. Once a match point is achieved, all parameters that led to the match are frozen.

Forecasting
i. Conduct performance prediction using various variables

ii. Set guidelines and constraint for the production forecasts.

iii. Evaluate the inflow and outflow well performance

iv. Run the prediction cases

v.
Sensitivity Analysis (what if component/parameter changes?)
Sensitivity analysis is one of the most useful features of the nodal analysis program that makes it flexible to made quick decision on the effect of changes on the production system (pressure and well rate. This flexibility is the basis of its optimization potential; since the direct effect of the particular parameter is seen on the rate. Thus, an optimal condition can be obtained and established. With this feature, the extent of how sensitive a component is or how it contributes to the pressure drop is obtained. The more its contribution to pressure drop, thus the more sensitive

i. Sensitize on various perceived inflow and outflow parameters and evaluate their effects on the total producing system.

ii. Compare scenarios for base case, low, and high

iii. Justify choice of optimum condition

iv. Give recommendations

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