Two common goals of Rate Transient Analysis (RTA) are the quantification of early time well performance using the Linear Flow Parameter (LFP), as well as Original Oil In Place (OOIP) volume being drained. These two parameters are essential for understanding the effects of completions, geology, and depletion which then advises different strategies for optimizing the economics of future development. This paper outlines limitations in the traditional RTA analysis of oil wells and proposes an improved workflow to better obtain values for LFP and OOIP.
A blind study of 10 Apache engineers was conducted to compare traditional methods with the new RTA workflow being proposed. The average error between engineers using traditional RTA methods exceeded 100% in some cases, while the use of the new proposed workflow yielded an average error of less than 10%. In addition to the enhanced consistency, the results proved more accurate when compared to numerical models. An additional benefit is that values generated by the new proposed workflow could be taken directly into a numerical model without the need for parameter modification to obtain historical matches.
One of the more commonly used methods for analyzing unconventional wells includes plotting the logarithm of rate vs. the logarithm of time (Wattenbarger et al. 1998). In this format wells in transient linear flow will exhibit a -1/2 slope. When the pressure transient reaches a boundary (usually from another fracture on the same well) it will transition into boundary dominated flow with a steeper production decline. An example of this is shown below on the left side of Figure 1.
Another common method of analysis is plotting inverse production rate vs. the square root of time (Wattenbarger et al. 1998). Wells in transient linear flow will show a straight line. When the pressure reaches a boundary, the production data diverges above the straight line, and is continuously curved upwards. This is shown on the right side of Figure 1.