What Is The Most Important Parameter in Calculating EUR?

Categories EUR, Reservoir Analysis

 

Modified Hyperbolic DCA (‘M-Hyp-DCA’) is the most widely used method in oil and gas production forecasting.

The main goal of production forecasting is to get the EUR, which is highly sensitive to parameters used in forecasting. The table below lists the parameters used in M-Hyp-DCA:

 

To understand “EUR sensitivity” in response to the above parameters, we changed only one variable at a time and kept the rest constant.

The relationships in summary:

  • EUR vs. qi: 100% linear relationship- As qi increases, EUR increases.
  • EUR vs. Di: 100% log-linear relationship- As log(Di) increases, log(EUR) decreases in a linear relationship.
  • EUR vs. b-factor: 99% linear relationship- As b-factor increases, EUR increases in a linear relationship.
  • EUR vs. Dsweff: 99% linear relationship- As Dsweff increases, EUR decreases in a linear relationship.
  • EUR vs. Well life: As well life increases, EUR increases up to a certain point and stays almost flat afterward.
  • EUR vs. qab: 100% linear relationship- as qab increases, EUR decreases in a linear relationship.

+-30% variation and effect on the EUR 

Table below shows the values for “-30%”, base, and “+30%” cases. The base case EUR is 851 Mbbl.

 

 

Using the above parameters, we estimated EURs for and calculated % difference from the base case EUR. The table below summarizes the results:

 

 

As shown in the above table, the variables with the highest effects on EUR are qi, b, Di, and Dsweff.

Normally, it is hard to miss getting the correct value for qi from production data. Di can also be estimated with 6-8 months of clean declining data. However, to get the b-factor, we need at least 18 months of data.

b-factor is important in reserve calculation. A 30% variation in b-factor can increase or decrease the EUR by almost 40%.

Dsweff depends on the late time flow regimes, which also makes it hard to estimate on early times.

Certain techniques help us estimate the b-factor and Dsweff, which we will discuss in more detail in future articles.

Related articles: How does b-factor change with completion and well spacing?