It is widely known that each well intervention proposal requires considerable dedication of human resources in terms of analysis, calculations and potential estimates, where Productivity Analysis plays a key factor in decision making and success of a job.
All this engineering allows us, effectively, not only to select the most suitable candidates for intervention, but also to evaluate the current production and the potential of production that will be obtained after carrying out operations in the well, including perforating, chemical/acid stimulation and hydraulic fracturing.
Productivity Analysis as an allied tool
In each work proposal, Productivity Analysis, known among petroleum engineers as Nodal Analysis, is an analytical technique that provides us with a close understanding of what is happening in the well in terms of energy and the fluid contributions to the production. It also allows us to evaluate the sensitivities of those parameters directly related to each type of intervention in the well.
There are several definitions for Productivity Analysis in a production system, one of the most accepted being its function as an analytical tool to forecast the performance of the different elements that make up the completion and production system.
This tool is used from the design of the well completion, ensuring that it is adequate to the production capacity of the reservoir, to the identification of restrictions or bottlenecks in the production system, as well as any mechanism to improve the efficiency of production.
Damage Factor as an evaluation parameter
We will focus on this point: improving production efficiency in a well. In well interventions, the key parameter evaluated is the formation damage factor, denoted as “S”.
It is true that flow efficiency is the best way to measure the result of an intervention. However, this efficiency is directly related to the value of “S”.
Determining well damage is often performed through the interpretation of pressure tests. However, many wells lack the appropriate mechanical setup to conduct these tests due to equipment limitations, the absence of downhole pressure sensors, the implementation of artificial lift systems, or conditions that complicate the interpretation of pressure behavior during the test.
In many cases, it is necessary to estimate this damage factor using mathematical methods, such as the turbulence effect in gas wells, or adjust it through sensitivity analysis and the analyst's experience.
How is this damage to the formation generated?
Simply by altering the original condition of any producing formation, damage is incurred in that formation. An example of this is during well drilling operations, mechanical completion and its connection with the producing sand, well production, and any interventions to enhance productivity.
Even during hydraulic fracturing operations, popularly known as fracking, although damage factors below zero (“0”) are obtained through pressure restoration tests, we will always be altering the original state of the formation.
Therefore, in most cases, except for the execution of hydraulic fracturing, this mathematical value will not reach the theoretical zero (“0”) that every stimulation and reservoir engineer hopes to achieve.
But what factors influence not reaching these values?
Mainly, several factors can influence the result, such as incorrect estimation of post-intervention production at the engineering level, selection of chemicals and agents for the intervention (which is a consequence of the first factor), and problems during the execution of the operation on site.
The reservoir or stimulation engineer must be cautious when making these estimates.
Although there are sensitivities that can achieve a skin factor of zero (“0”), it is critical to note that this should be considered the maximum potential when interpreting analysis results and presenting them to the decision-making team.
In any case, it is recommended to perform stochastic analyzes to broadly address the different scenarios that could arise. This is because, regardless of the degree of technical/operational maturity, among other factors, recurring problems are a possibility that must always be kept in mind.