Analysis of the Acoustic Velocity of Gas from Fluid Level Tests in Producing Heavy Crude Shallow Wells with Cyclic Steam and Nitrogen Stimulation, Colombia

Abstract

The fluid level software provides useful information to optimize oil and gas production when is required. The fluid level calculation is given by the acquisition of the half travel time of a soundwave and its acoustic velocity, which is highly influenced by changes in temperature, pressure, and specific gravity of gas, commonly seen in cyclic steam and nitrogen stimulations. Considering the above concept, a process for collection and statistical analysis of acoustic velocities was developed in a heavy oil field in order to ensure accuracy in fluid level detection in two specific groups of horizontal shallow wells whose gas composition was constantly altered by two different thermal EOR stimulations. The first group contains wells injected with cyclic steam, called EOR-1, and the second group includes wells injected with cyclic steam + nitrogen simultaneously, called EOR-2. Additionally, an estimation of the specific gravity of gas was calculated as a function of gas temperature and acoustic velocity collected, assuming an ideal mixture of gases at determined temperature ranges, considering the behavior of the casing pressure ​​as a constant (less than 2 Psig average). Scatter and box-plot were made using descriptive and inferential statistical methods for the study of data. With the analysis of the acoustic velocity of gas not only was possible to create a unique reference pattern with specific statistical Tukey's fences to improve the accuracy of liquid level detection by means of outlier determination, but it could also be interpreted the behavior of the annular gas composition in presence of additional gases such as water vapor and nitrogen at different annular gas temperature ranges during their whole production cycle, without requiring an expensive chromatographic analysis. In the same way, a detection method of nitrogen channeling between wells of the same producing sand could be established regardless of the EOR methodology performed, since it was determined that acoustic velocities from 1290 ft/s to 1400 ft/s are highly related to the presence of nitrogen in the gas composition being considered atypical in steam-injected wells (EOR-1), whose determined range varies from 1400 ft/s to 1520 ft/s.